MOTIONRefer to video: Motion Visualized) Till now we have described motion mathematically. But this...

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MOTION

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IX – Std. Motion – Class notes I

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Instructions: This booklet given to you is your Class Notes. Keep filling this sheet as the class proceeds.

At the end of this session, you will have your notes ready.

1. Introduction

(Refer to video: Understanding Motion)

a. Concept of Rest and Motion

Question1.A person travelling with you in a bus is at rest. Do you agree with the statement?

Motion is one of the most important topics in physics. You can say that physics or natural

enquiry essentially began with ‘motion’. We see a lot of objects around us that are moving.

For instance, we see cars running on roads, birds flying etc. While other objects like

buildings appear to be at rest. But the same buildings seem to be in motion if viewed from

a moving car.

Don't forget that even if you appear to be standing still, the Earth is moving around the Sun,

and the Sun is moving around our galaxy. The galaxy itself is speeding around at great

speeds, even at speed greater than speed of light.

Question2. How can the galaxies move apart at a speed greater than the speed of light? Doesn’t this

violate Einstein’s theory?

Did You Know?

Aristotle noted that objects given an initial push along the ground (or

on a tabletop) always slow down and stop. Consequently, Aristotle

argued, the natural state of an object is to be at rest. Galileo, the first

true experimentalist, re-examined horizontal motion in the 1600s and

found it was not true!

So when do we say that a body is moving? Does it have to do anything with the observer?

Or is it an absolute term?

b. Frame of Reference

Motion is a relative term. There is nothing as ‘absolute motion’. We inherently assume that

we are at rest and we try to measure motion relative to us. An object is said to be at rest

with respect to another object if it does not change its position with respect to the other

object. If it changes its position, then it is said to be in motion.

Motion of a body is observed by attaching a frame of reference to an observer and we

measure the change in position of the body relative to that frame.

https://en.wikipedia.org/wiki/Frame_of_reference

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Figure 1: Frame of Reference

For example, suppose a person A is standing on a cart, which is moving with constant

velocity, and he throws a ball vertically upwards. Now we analyze the motion of ball. If the

cart itself is our reference frame, the motion of ball is straight line as observed by A. But if

our reference frame is attached to ground, the motion of the ball is somewhat curved as

seen by observer B.

Now that we know what a reference frame is and how to determine whether an object is

moving or not, let us quantify this motion.

2. Distance and Displacement

(Refer to video: Distance and Displacement)

Motion is basically change in position of a body with time. This change in position can be

measured using:

Distance

Displacement

Suppose a person wants to go from point A to point B. There can be different ways to do so.

He can take the path ACB or ADB or AEB.

Figure 2: Distance and Displacement

The lengths of paths ACB, ADB or AEB are the actual length of path that the person has to

cover. This is represented by distance. Distance is the length of actual path traversed by a body.

It is a scalar quantity having only magnitude, and no direction.

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On the other hand, to reach at point B by covering the least distance, he must take the path

ADB. Displacement is the shortest distance between the initial and final positions. It is a vector

quantity, having both magnitude and direction.

Did You Know?

An instrument called odometer measures the distance travelled by vehicles.

About 15 BC, the Roman architect and engineer Vitruvius mounted a large

wheel of known circumference in a small frame; when it was pushed along

the ground by hand it automatically dropped a pebble into a container at

each revolution, giving a measure of the distance traveled. It was, in effect,

the first odometer.

Question3. A car is moving in a circular path of radius 2 m. Calculate both the distance and the

magnitude of the displacement of the car after i) one complete revolution ii) one-half revolution iii)

one-fourth revolution. What can you conclude about the relationship between distance and

displacement?

3. Time, Average Speed and Velocity

(Refer to video: Time, Average Speed and Velocity)

For a moving body, apart from distance and displacement, it is also important to know how fast

the body is moving. This introduces the concept of speed and velocity.

a. Speed, Average Speed and Instantaneous Speed

Speed of a body is the rate of change of distance with time.

𝑆𝑝𝑒𝑒𝑑, 𝑣 =𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒, 𝑠

𝑇𝑖𝑚𝑒, 𝑡

When a body covers equal distances in equal intervals of time, it is said to have a uniform

speed; else it has a non-uniform or variable speed.

Speed is a scalar quantity. To specify the speed of an object, we require only its magnitude.

Its SI unit is m/s.

Now we are going to learn how instantaneous speed differs from average speed!

When a cop pulls you over for speeding, it’s because of your instantaneous speed, or speed

at which you were driving at that particular instant. This is different from your average

speed, which takes into account how long it took you to complete your journey and the

distance you traveled. In the course of entire journey you might have over-sped, sometimes

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you might have halted. However, measuring average speed assumes that you travelled at

the same speed for the entire trip.

𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝑠𝑝𝑒𝑒𝑑, 𝑣𝑎𝑣𝑔 =𝑇𝑜𝑡𝑎𝑙 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑡𝑟𝑎𝑣𝑒𝑙𝑙𝑒𝑑

𝑇𝑜𝑡𝑎𝑙 𝑡𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛

Question4.What does the speedometer of a vehicle show: average speed or instantaneous speed?

Explain.

Did You Know?

On Saturn, wind speeds can reach as high as 1609 km/h, which is just about

as fast as a speeding bullet. The highest wind speed ever recorded on Earth

during a hurricane was in 1996, during Tropical Cyclone Cynthia when

gusts reached 408 km/h.

b. Velocity

Sometimes speed is not sufficient to describe motion of a body. The rate of motion will be

more complete if it also involves the direction of motion. For this, we define a new term

called “velocity”. Velocity is basically speed of a body moving in a definite direction.

Velocity can be defined as displacement per unit time. It is a vector quantity having both

magnitude as well as direction.

𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦 =𝐷𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡

𝑇𝑖𝑚𝑒

Just as in case of speed, here also we have average and instantaneous velocity.

𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 =𝑇𝑜𝑡𝑎𝑙 𝐷𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡

𝑇𝑜𝑡𝑎𝑙 𝑡𝑖𝑚𝑒

For a body whose velocity is changing at a uniform rate, the average velocity is given by

the arithmetic mean of initial velocity and final velocity for a given period of time.

𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 =𝐼𝑛𝑖𝑡𝑖𝑎𝑙 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 + 𝐹𝑖𝑛𝑎𝑙 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦

2=

𝑢 + 𝑣

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http://www.crh.noaa.gov/fsd/?n=saturn

http://www.wmo.int/pages/mediacentre/infonotes/info_58_en.html

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Misconception: The average velocity is given by arithmetic mean of initial and

final velocities.

Clarification: The average velocity is given by arithmetic mean of initial and

final velocities only when it is changing at a constant rate or the acceleration is

constant.

Question5.Under what conditions would the speed of a body be equal to the magnitude of velocity?

Question6.A train takes 2 hrs to reach station B from station A and 3 hrs to return back to A. Stations

A and B are separated by a distance of 400 km. What is the average speed and velocity of the train?

4. Acceleration

(Refer to video: Acceleration)

If a body is in non-uniform motion, its velocity does not remain constant. Acceleration is the

rate of change of velocity with respect to time. It is a vector quantity.

𝐴𝑐𝑐𝑒𝑙𝑒𝑟𝑎𝑡𝑖𝑜𝑛, �⃗� =𝐶ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦

𝑇𝑖𝑚𝑒=

𝑣 − 𝑢

𝑡

This is the average acceleration over a period of time t. It is quite possible that the instantaneous

acceleration will be different at different points of time.

If the velocity increases with time, the body is said to be accelerated. Else it is said to be

decelerated (or retarded).

Misconception: Acceleration always occurs in the same direction, as an object

is moving.

Clarification: Acceleration need not be in the same direction as motion. It can

be at any angle to the velocity.

Did You Know?

The thrill of roller coasters is not due to their speed, but rather due

to their accelerations and to the feelings of weightlessness and

weightiness that they produce. Roller coasters are all about

acceleration; that's what that make them thrilling!

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Question7.How uniform acceleration differs from non-uniform acceleration?

When a body falls freely under gravity, the acceleration produced in the body is called the

acceleration due to gravity (g). The average value of g near earth’s surface is 9.8 m/s2 or 10

m/s2 and it always act towards center of earth.

Question 8.A car is moving with a velocity of 40 m/s. The brakes are applied to retard it at a rate of 2

m/s2. What will be its velocity after 5 s of applying the brakes?

Did You Know?

The value of acceleration due to gravity is not constant. It varies with depth as well as altitude. Even on earth’s surface, it is more at the poles compared to the equator.

5. Motion Visualized

(Refer to video: Motion Visualized)

Till now we have described motion mathematically. But this mathematical representation does not

help us visualize the motion; hence we switch to the graphical approach, which uses the coordinate

system to represent the motion.

Independent variable (time) is measured on the x-axis while the dependent variable (displacement,

velocity, acceleration etc.) is measured on the y-axis. Basically it shows the variation of dependent

quantity with independent quantity.

Figure 3: Graphical Representation of a Quantity

Question 9.What do you mean by slope of a graph? What is its physical significance?

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a. Displacement-Time Graph

The slope of the displacement-time graph gives the velocity of the object.

i) Body at Rest

Figure 4: Body at Rest

Question 10.How will the displacement time graph of two bodies – one having greater velocity and the

other having less velocity (both velocities being constant) look like?

ii) Body moving with non-uniform velocity

Instantaneous velocity at A = tan θ

Figure 5: Body moving with positive acceleration

Question 11.How will the displacement time graph of a body moving with a non-uniform velocity and

negative acceleration?

b. Velocity-Time Graph

The slope of the velocity-time graph gives the acceleration of the object.

i) Uniform Velocity

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Figure 6: Uniform Velocity

i) Uniform Acceleration

Figure 7: Uniform Acceleration

The area under the velocity-time graph gives the displacement during that time.

Figure 8: Area under Velocity-Time Graph

Question 12.The following graph shows the velocity-time graph of a body. Plot the corresponding

displacement-time and acceleration-time graphs.

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6. The Equations of Motion

(Refer to video: The Equations of Motion)

For bodies moving with a constant acceleration, the motion is guided by the following three

equations:

Figure 9: Body with Uniform Acceleration

First equation of motion:

𝑣 = 𝑢 + 𝑎𝑡

Second equation of motion:

𝑠 = 𝑢𝑡 +1

2𝑎𝑡2

Third equation of motion:

𝑣2 = 𝑢2 + 2𝑎𝑠

Motion can either be 1-D (if the object moves in a straight line), 2-D (if it moves in a plane along a

curved path) or 3-D (if it moves in space).

Misconception: If an object has zero velocity, its acceleration is also zero.

Clarification: If an object has zero velocity, its acceleration need not necessarily be

zero. Think about a ball thrown upwards

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It is very important to note that the equations of motions can only be used when acceleration is constant.

Question 13.A balloon starts from the ground and moves vertically upwards with an acceleration of 2

m/s2. After 5s, a stone is released from the balloon. Find the time taken by the stone to reach the ground.

Also calculate the net distance covered and displacement of the stone from the moment it is

released.

7. Uniform Circular Motion

(Refer to video: Uniform Circular Motion)

Uniform circular motion can be described as the motion of an object in a circle at a constant speed.

As an object moves in a circle, it is constantly changing its direction. At all instances, the object is

moving tangent to the circle.

Figure 10: Uniform Circular Motion

𝑆𝑝𝑒𝑒𝑑 =2𝜋𝑅

𝑇

Misconception: The velocity of a body is constant in uniform circular motion.

Clarification: The speed of a body is constant in uniform circular motion; not the

velocity.

Question 14.What can you say about the acceleration of a body undergoing uniform circular motion?

Did You Know?

The acceleration of a body in uniform circular motion is called

centripetal acceleration. Centripetal simply means “center

seeking”! It is always directed towards the center and is directly

proportional to square of velocity.

Question 15.A cyclist goes around a circular track once every 2 minutes. If radius of the circular track

is 110 m, calculate the speed of cyclist. What is his average velocity?

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IX – Std. Motion – Homework

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Instructions: This booklet given to you is your Homework Sheet. Solve these problems at home. You

shall be exam-ready if you can finish all the problems.

1. A body covers some distance along a curved path. Can it have a zero average velocity?

2. A body covered a distance of ‘x’ meters along a semicircular path. Calculate the magnitude of

displacement of the body and the ratio of the distance covered to the displacement?

3. A boy runs for 10 minutes at an uniform speed of 18 km/h. At what speed should he run for the

next 20 minutes so that the average speed comes 12 km/h?

4. How does average velocity differ from instantaneous velocity? Explain with a velocity time

graph.

5. David goes from his home to school at a uniform speed of 𝑢 m/s and returns back at 𝑣 m/s. If

the distance between his home and school is 𝑑 meter, find his average speed and average

velocity.

6. Brakes are applied to a car so as to produce a retardation of 5 m/s2. If the car takes 1.5 s to stop

after applying the brakes, calculate the distance travelled by it?

7. A person walks along the sides of a square field each side is 200 m long. What can be the

maximum and minimum displacement of the person?

8. Two stones are thrown vertically upwards simultaneously with their initial velocities 𝑢1 and 𝑢2

respectively. Prove that the heights reached by them would be in the ratio of 𝑢12: 𝑢2

2.

9. Which of the two bodies (A and B) has

A) Greater velocity

B) Greater acceleration

10. A body starts from rest and moves with a uniform acceleration of 5 m/s2 for 5 s and then it

moves with a constant velocity for 4 s. Later it slows down and comes to rest in 5 s. Draw the

velocity graph for the motion of the body. Also calculate its net displacement.

11. The velocity-time graph of a body is shown below.

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How can we calculate its average velocity? Can we use the formula 𝑣𝑎𝑣 =𝑢+𝑣

2 to calculate the

average velocity?

12. A cyclist moving on a circular track of radius 50 m completes one revolution in 4 minutes.

What is his

A) Average speed

B) Average velocity

in one full revolution?

13. A ball is dropped from a building of height ℎ meter. Calculate the distance travelled by it in

𝑛𝑡ℎ second.

14. Differentiate between

A) Distance and displacement

B) Speed and velocity

15. What can you say about the speed, velocity and acceleration of a body undergoing uniform

circular motion?

16. Which of the following quantities can be obtained from a velocity-time graph?

I. Velocity

II. Displacement

III. Acceleration

A) I and II

B) II and III

C) I and III

D) I, II and III

17. In which of the following cases will the displacement be equal to distance?

A) Earth revolving around sun

B) Pendulum moving to and fro

C) Car moving in a straight line

D) None of these

18. If the displacement of a body is directly proportional to square of time, the object moves with

A) Uniform velocity

B) Uniform acceleration

C) Increasing acceleration

D) Decreasing acceleration

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19. The maximum height to which a body will rise if thrown with an initial velocity is

A) 𝑢/𝑔

B) 𝑢2/𝑔

C) 𝑢2/2𝑔

D) 𝑢/2𝑔

20. Slope of an acceleration-time graph gives us

A) Velocity

B) Displacement

C) Jerk

D) None of these

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LAWS OF MOTION

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IX – Std. Laws of Motion – Class notes

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Instructions: This booklet given to you is your Class Notes. Keep filling this sheet as the class

proceeds. At the end of this session, you will have your notes ready.

1. Introduction

(Refer to video: Basics)

Question 1.When you slap someone, in physics terms, you should not feel sorry. Can you think why?

c. Concept of Force

A body is said to be in motion if it changes its position with respect to the frame of

reference; else it is said to be at rest. We already have learnt about the equations, which

guide the motion of anybody moving with constant acceleration. But what exactly causes

this motion? Do all motions require a cause? How can you bring a change in the state of

motion? In this chapter, we are going to learn about the laws that govern this motion. The

applications of these laws of motion are truly limitless.

For years “rest” was thought to be the natural state of motion. Aristotle put forward this

concept that all bodies have a tendency to come to rest eventually and a force is required to

keep the body moving. However, later this theory was proved wrong.

In the most basic terms force can be defined as a push or a pull on an object. Whenever

there is an interaction between two objects, there is a force upon each of the objects. When

the interaction ceases, the two objects no longer experience the force.

Force is a vector quantity, having both magnitude as well as direction. Its SI unit is Newton

(N). When a number of forces act on a body, there comes the concept of resultant force,

which can either be balanced or unbalanced.

d. Balanced and Unbalanced Forces

If the resultant of all forces acting on a body is zero, forces are said to be balanced. If the

resultant doesn’t sum up to zero, forces are said to be unbalanced.

It is important to note that as force is a vector quantity, it must be added vectorially to find

the resultant force.

Figure 11: Balanced and Unbalanced Forces

Newton put forward three laws of motion, which define the motion of bodies.

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2. First Law of Motion

(Refer to video: First Law of Motion)

a. Galileo’s Experiment

Galileo was the first person to conclude that even when the force applied to set a body in

motion is withdrawn, it will remain in motion provided no other restraining force acts on

it. Newton's first law of motion relies on Galileo's thoughts about motion according to

which a force is not needed to keep an object in motion.

Figure 12: Galileo’s Experiment

Question 2.A ball when slid on a horizontal surface eventually comes to a stop, even though

seemingly no force is acting on it. Doesn’t this contradict Galileo’s statement?

Newton formulated this concept in form of Newton’s first law of motion.

b. 1st Law of Motion

According to Newton's First Law of motion, an object will remain at rest or in uniform

motion in a straight line unless acted upon by a net unbalanced external force.

Figure 13: Newton’s 1st Law of Motion

The property of a body by virtue of which it resists a change in its state of motion is known

as inertia. It is an inherent property of each body. All objects have this tendency - they have

inertia. But not all objects have the same magnitude of this tendency! Mass is the quantity

that determines the inertia of a body. A more massive object has a greater tendency to resist

change in its state of motion and hence greater inertia.

Newton’s 1st law is also known as Law of Inertia.

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Misconception: If an object is at rest, no forces are acting on the object.

Clarification: If an object is at rest, forces might be acting on it, but their

net result is zero i.e. they are balanced forces.

Question 3.Suppose two bodies of mass 2 kg and 10 kg are placed on a frictionless surface. The force

required to move either of them is the same. Does that mean both bodies have same inertia? Give

reasons for your choice.

Did You Know?

Newton’s laws of motion are also valid for liquids and

gases. And that is why dizziness occurs after getting out of

the elevator, as blood in the body keeps moving down even

after the elevator stops.

Question 4.Why is it so that when a bus suddenly starts moving, the passengers tend to fall backward

and when it stops suddenly, the passengers tend to lean forward?

Question 5.If an elephant was chasing you, its enormous mass would be most threatening. But if you

moved in a zigzag path, its big mass would become your advantage. Why?

Many other day-to-day phenomena can be explained using the concept of inertia and

Newton’s first law of motion:

On shaking a tree, the fruits fall down.

On striking a pile of coins in a game of carrom, only the bottom most coin moves

while the rest of the pile remains intact.

An athlete often runs before taking a long jump

When a person jumps out of a moving train, he falls down

In order to remove dust from a carpet and clean it, it is beaten with a stick.

Now let’s discuss what the second law of motion is and how it provides a quantitative

measure of the net force acting on a body.

3. Second Law of Motion

(Refer to video: Second Law of Motion)

a. Linear Momentum

Linear momentum is one of the quantities that measure the motion of a body. It is defined

as the product of an object’s mass, m, and its velocity, v and is denoted by the letter 𝑃⃗⃗⃗⃗ .

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�⃗⃗� = 𝑚�⃗�

Momentum is a vector quantity. A body’s momentum is always in the same direction as

its velocity. The SI unit of momentum is kg-m/s.

b. Change of momentum and 2nd Law

Figure 14: Graphical Representation of Newton’s 2nd Law of Motion

According to Newton’s 2nd law of motion, the net external force applied on a body is

equal to the rate of change of its momentum.

�⃗� =�⃗⃗�

𝑡

But

�⃗⃗� = (𝑚�⃗�)

If 𝑚 is constant,

�⃗⃗� = 𝑚�⃗�

�⃗⃗�

𝑡= 𝑚

�⃗�

𝑡

But we know that, �⃗� =�⃗⃗�

𝑡

Hence,

𝑅𝑎𝑡𝑒 𝑜𝑓 𝑐ℎ𝑎𝑛𝑔𝑒 𝑜𝑓 𝑚𝑜𝑚𝑒𝑛𝑡𝑢𝑚 = 𝑚�⃗�

Misconception: As per 2nd law of motion, 𝐹 = 𝑚𝑎

Clarification: This is valid only when mass is constant. However this force

is always equal to rate of change of momentum, irrespective of whether

mass is constant or not.

Question 6.While catching a ball, the cricketer withdraws his hands. Does this reduce the momentum

change of the ball? How is it advantageous?

Question 7.How do airbags reduce damage to the passengers during an accident?

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Misconception: The motion of a body is always in the direction of net

external force applied to the object.

Clarification: It’s not the motion, but the change in momentum that is

always in the direction of net external force applied to a body.

Question 8.A rightward force of 302 N is applied to a 28.6-kg crate resting on the floor. If the

coefficient of friction between the crate and the floor is 0.750, find the acceleration of the crate.

Question 9.As a rocket is fired from a launch pad, its speed and acceleration increase with time as its

engines continue to operate. Explain why this occurs even though the thrust of the engines remains

constant.

4. Conservation of Momentum

(Refer to video: Conservation of Momentum)

Before we learn about conservation of momentum, it is important to understand what a

system is and once we define a system, what internal and external forces are.

A system is a portion of the universe chosen for analysis. Everything outside of the system is

known as the surrounding.

Suppose we have three bodies A, B and C. If we choose A and B as our system, any force that

these bodies exert on each other is an internal force. While any force exerted on the system by

C or any other body outside the system is an external force.

Figure 15: Concept of System

We know that,

�⃗�𝑒𝑥 = 𝑅𝑎𝑡𝑒 𝑜𝑓 𝑐ℎ𝑎𝑛𝑔𝑒 𝑜𝑓 𝑚𝑜𝑚𝑒𝑛𝑡𝑢𝑚

If F⃗⃗ex = 0,P⃗⃗⃗ = 0, i.e. the momentum remains conserved.

According to law of conservation of momentum, the total momentum of a system remains

conserved if no external forces act on it.

Misconception: During conservation of momentum, we need to take algebraic

sum of momenta.

Clarification: Since momentum is a vector quantity, we need to take vector

sum of momenta to calculate the net momenta.

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For an isolated system of two bodies,

𝑚𝐴�⃗⃗�𝐴 + 𝑚𝐵 �⃗⃗�𝐵 = 𝑚𝐴�⃗�𝐴 + 𝑚𝐵�⃗�𝐵

Figure 16: Conservation of Momentum during Collision of Two Bodies A and B

Question 10.Two bullets, travelling in opposite directions with a speed of 500 m/s and 250 m/s

collide with a stationary block of mass 12kg. If the bullets stick to the block and they move together,

find the final velocity of the system. Assume surface to be frictionless.

Misconception: During collision, total energy is conserved before and after

collision.

Clarification: During collision, total momentum remains conserved, if no

external forces are acting. Energy remains conserved only in some special

cases.

Did You Know?

In an explosion, an internal impulse acts in order to propel the parts

of a system into a variety of directions. After the explosion, the

vector sum of momenta of individual parts of the system equals the

momentum before explosion. Explosion is similar to reverse of

collision!

5. Third Law of Motion

(Refer to video: Third Law of Motion)

a. Action, Reaction and 3rd Law

The third law of motion explains how a force acts on an object. It states that, to every

action there exists an equal and opposite reaction. And these forces act on two different

bodies.

In the interaction of two bodies A and B,

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�⃗�𝐴𝐵 = −�⃗�𝐵𝐴

Figure 17: Interaction between Two Bodies A and B

Question 11.Do action and reaction forces act simultaneously? Explain.

Question 12.Can you walk on a frictionless surface? Why / Why not?

Examples of action-reaction forces:

i) Firing a bullet from a gun:

Figure 18: Recoil of a Gun

ii) Rocket propulsion

Figure 19: Propulsion of Rocket

iii) Swimming – Person pushes water backwards. In turn, water pushes him/her

forward.

Misconception: In an interaction between two bodies, the more massive

object exerts a greater force than the less massive object.

Clarification: The force exerted by both the bodies is equal in magnitude.

However the less massive body will have greater acceleration.

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Question 13.When a horse exerts a force on cart, the cart exerts an equal and opposite force on the

horse. Then how come the horse can manage to pull the cart?

Did You Know?

As per Newton’s 3rd law of motion, a single isolated force can’t

exist in nature. Forces always exist in pairs!

b. Newton’s Second Law as the Fundamental Law

As per 2nd law of motion,

�⃗� =�⃗⃗�

𝑡

If mass is constant,

�⃗� = 𝑚�⃗�

If �⃗� = 0, �⃗� = 0

This is basically the first law of motion.

If

�⃗� = 0, �⃗⃗� = 0

This means that momentum remains conserved, which is the law of conservation of

momentum.

Question 14.Can you arrive at Newton’s 3rd law using Newton’s 2nd law?

c. Limitations of Newton’s Laws of Motion

The scope and applications of Newton’s laws of motion are widely immense. Although

these laws are widely used, they don’t always work. These are basically approximation of

realities.

The frames of references where Newton’s laws hold true are known as inertial frames of

reference. Any frame of reference that is at rest or moving with a constant velocity with

respect to an inertial frame of reference is also inertial. While those in which Newton’s

laws don’t hold true are known as non-inertial frames of reference.

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Did You Know?

In non-inertial frames of reference, some 'extra forces' have

to be invoked to retain Newton's laws of motion. These

forces are known as fictitious forces or pseudo forces.

Newton’s laws of motion fail in the following conditions:

i) At quantum level. e.g. to explain motion of electrons around nucleus

ii) When the velocities involved approach the speed of light.

iii) Non-inertial frames (accelerated frames)

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IX – Std. Laws of Motion – Homework

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1. An object experiences a net zero external unbalanced force. Is it possible for the object to be

travelling with the non-zero velocity? If yes, state the conditions that must be placed on the

magnitude and direction of the velocity. If no, provide a reason.

2. When a carpet is beaten with a stick, dust comes out. Explain, why?

3. Why is it advised to tie any luggage kept on the roof of a bus with a rope?

4. Using a horizontal force of 200 N, we intend to move a wooden cabinet across a floor at

constant velocity. What is the force of friction that will be exerted on the cabinet?

5. The change in momentum of a body in 0.01 s is 10kg m/s. Find the force acting on this body.

6. Why is it easier to stop a tennis ball than a cricket ball moving with same speed?

7. Akash experienced a net force of 1800 N at the bottom of a roller coaster loop. If his mass is

75 kg, what can you say about his acceleration at this point?

8. A canon of mass 1500 kg fires a shell of mass 15 kg with velocity 150 m/s. Calculate velocity

of recoil of the canon.

9. What do you mean by balanced and unbalanced force? Give examples.

10. When the brakes are applied to the bike the person sitting on the back seat moves forward.

Why?

11. Imagine a block of mass ‘m’ placed on a table. Do the weight of the block and normal form

an action-reaction pair? Why/Why not?

12. What would be the weight of a body of mass 50 kg on the surface of the moon, where g = 1.6

m/s2. What would be its mass?

13. A body of mass 5 kg undergoes a change in speed from 30 to 40m/s. Calculate the increase in

its momentum?

14. If a body is moving towards right, the net force on it must also be towards right. Do you agree

with this statement? Justify.

15. Explain why some of the leaves may get detached from a tree if we vigorously shake its

branch.

16. The two factors on which the momentum of a body depends are ______ and _________.

A) Velocity and time

B) Mass and velocity

C) Mass and distance

D) Mass and velocity

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IX – Std. Laws of Motion – Homework

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17. Momentum of massive object at rest is _______.

A) Very large

B) Very small

C) Zero

D) Not defined

18. An example for a vector quantity is ________.

A) Speed

B) Momentum

C) Distance

D) Length

19. S.I. unit of impulse is ______

A) N-s

B) N-s2

C) Kg-m/s2

D) Kg-m2/s2

20. The momentum of a toy bus of 0.01 kg moving with a velocity of 5 m/s is

A) 0.005 kg m/s

B) 0.05 g m/s

C) 0.005 N s

D) None of these

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GRAVITATION

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IX – Std. Gravitation – Class notes

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1. Introduction

(Refer to video: The Story of Gravity)

a. Gravitation as a Universal Force

Question 1.We know that we are bound to the Earth because of gravity. How far do you think the

gravitational pull of the earth extends?

Gravity is the universal force of attraction acting between matters. It is one of the four

fundamental forces known in nature, along with the electromagnetic, strong and weak nuclear

forces. Of these forces, gravity is the weakest and thus plays negligible role in determining the

internal properties of everyday matter. On the other hand, gravity is something that keeps us

bound to the ground, keeps the moon circling the earth and the earth circling the sun. It controls

the trajectories of bodies in the universe and the structures and evolution of stars, galaxies and

the whole cosmos.

Many theories have been put forward in an attempt to explain gravity. Galileo (1564-1642) first

explored the motion of falling objects. Isaac Newton (1642-1727) later described the law of

gravity. In this chapter we are going to focus on Newton’s theory of gravitation. As per

Newton’s theory of gravitation, gravity is a force- one that attracts all objects having mass to

all other objects having mass.

Do You Know?

Gravity cannot be fumed off or shielded in any way. Intervening objects

have no effect on the original gravity force between two separated

masses. This means that there is no antigravity chamber available in

which the occupants can continually float freely. Orbiting astronauts

appear weightless because their fall towards the earth is balanced by the

outward directed centrifugal force.

Before we discuss Newton’s law of gravitation, let us first have an insight into the three laws

of planetary motion proposed by Kepler in the early 1600s. Kepler basically summarized the

carefully collected data of his mentor - Tycho Brahe – that described the motion of planets in

the solar system. Kepler's laws paved a way for the development of celestial mechanics, i.e.,

the application of the laws of physics to the motions of heavenly bodies.

b. Kepler’s Laws of Planetary Motion

http://www.britannica.com/topic/universe

http://www.britannica.com/topic/Cosmos-astronomy

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Kepler's three laws of planetary motion can be described as follows:

i) Law of Orbits:

This law states that the path of planets around the sun is elliptical in shape, with the

center of the sun being located at one of the two foci of the ellipse.

Figure 20: Law of Orbits

ii) Law of Equal Areas:

As per the law of equal areas, an imaginary line drawn from center of the sun to

center of the planet sweeps out equal areas in equal intervals of time.

Figure 21: Law of Equal Areas

iii) Law of Periods:

The law of periods states that the ratio of the squares of the time periods of any two

planets around the sun is equal to the ratio of the cubes of the semi-major axis of its

orbit.

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Figure 22: Law of Periods

Mathematically it can be expressed as,

𝑇12

𝑇22 =

𝑅13

𝑅23

Question 2.Using Kepler’s laws of planetary motion; prove that the gravitational force is inversely

proportional to the square of the distance. Assume the orbits to be circular.

2. The Universal Law

(Refer to video: The Universal Law)

Next comes Galileo, a 17th century physicist who gave us three basic information, which is a

common knowledge now but wasn’t before his time.

1. All things fall at the same rate irrespective of their mass.

2. Free fall is not a constant velocity motion but an accelerated motion. Anything near

earth falls at the rate of 9.8 m/s2 or 32 ft/s2.

3. Velocity of a body doesn’t change until unless you apply a force.

Isaac Newton, an English Physicist and Mathematician had all these knowledge at his

disposal. That is why he said “If I have seen further, it is by standing on the shoulders of

giants.”

We all know the apple story. But he did not ask the question “Why does apple fall?”. It was

known that earth pulls everything towards it. Rather he asked the question, “ If apple falls,

does the moon also fall?” Answer turned out to be “yes” and he had found that same force is

responsible for falling of the apple and falling of the moon. At that time he had already found

laws of the motion and using Kepler’s 3rd law he found out the force is inversely proportional

to the square of distance between bodies.

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He finally assembled all the information into one single law known as Newton’s Universal

Law of Gravitation. It says ever object having mass attracts every other object having mass

with a force called gravitational force and, Newton’s major accomplishment was not that it

says, Sun attracts the earth or earth attracts the moon or earth attracts earthly things but his

major accomplishment was to say that everything attracts every other thing and that needs

courage to say because there are million ways to prove that wrong if it turned out to be a

wrong theory.

Newton's law of universal gravitation states that any two-point masses in the universe attract

each other with a force that is directly proportional to the product of their masses and inversely

proportional to the square of the distance between them. And it acts along the line joining the

point masses.

𝐹 ∝𝑚1𝑚2

𝑟2

Well, a point mass is a point particle with a nonzero mass and no other properties or structure.

Figure 23: Gravitational Force between Two Point Masses

Eliminating the proportional sign,

𝐹 = 𝐺𝑚1𝑚2

𝑟2

Where, G is the universal gravitational constant. It is numerically equal to the force of attraction

between two point masses each of 1 kg, separated by a distance of 1 m.

G = 6.67 × 10−11Nm2/kg2

Question 3.Why is the gravitational force always attractive in nature?

Uniform spherical bodies (shells or solid spheres) can be considered as point masses and that

their whole mass is concentrated at the center. And the formula for gravitational force between

point masses can be directly used for uniform spherical bodies.

𝐹 = 𝐺𝑚1𝑚2

𝑟2

https://en.wikipedia.org/wiki/Mass

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Figure 24: Gravitational Force between Two Spherical Bodies

Misconception: There is no gravity at the center of the Earth.

Clarification: There is gravity everywhere; even at the center of the earth.

However, if you were at the center of the Earth you would feel weightless. This is

because all the forces on you that result from the Earth's gravity are balanced.

Do You Know?

Gravitational attraction does not depend on the composition of bodies;

it depends only on their mass. Several blocks composed of glass, tin,

ice, or, any other material, if they all have equal mass, they will attract

any other given body with the same gravitational force.

Question 4.If the mass of a satellite orbiting the Earth is doubled, how should its speed vary so that

radius of the orbit remains unchanged?

Question 5.Why aren’t we attracted to each other, even though gravitational force acts between us?

Do You Know?

The Cavendish experiment was the first experiment that measured the

force of gravity between masses in the laboratory and also yielded

accurate value for the gravitational constant G. British scientist Henry

Cavendish performed it in 1797-1798. And he named his paper,

“Weighing the Earth” as once value of G is known, we can easily find,

Mearth i.e. mass of the earth.

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Question 6.Two planets of mass ‘m’ and ‘16m’ and radii ‘r’ and ‘2r’ are separated by a distance of

‘10r’. Determine the point where a particle of some mass will not experience any gravitational

force.

Now that we have a qualitative and quantitative idea of gravitational force, let’s examine the

motion of the only natural satellite of the earth! The Moon!

3. The Moon’s Falling

(Refer to video: The Moon’s Falling)

a. Moon Orbiting the Earth

Two bodies attract each other with the same gravitational force. However, a falling apple does

not affect the earth at similar scales (The earth doesn’t seem to move towards the apple). On

the other hand, the moon does affect the earth. High and low tides are caused because of

gravitational pull of the moon.

Question 7.What is the reason for this difference in behavior that we see only lighter body getting

accelerated towards the heavier body?

The moon moves around the earth in nearly circular orbits with some speed.

Figure 25: Moon Rotating around the Earth

The forces of speed and gravity keep the Moon in a constant orbit around Earth. With the right

combination of speed and gravity, satellites (here Moon) can fall around the body, instead of

into the body that they orbit (here Earth).

The gravitational force between the earth and moon provides the necessary centripetal force to

the moon to keep it moving in circular path. And because of its velocity (there is no friction to

slow down its motion) it doesn’t collapse into the earth.

b. Centripetal force

For any object to move in a circular path, it requires some centripetal (i.e. center seeking) force.

Any real force like tension, normal or gravitational force, can provide this force.

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Figure 26: Centripetal Force

e.g. when we rotate a stone tied to a string, it’s the tension in the string that provides the required

centripetal force.

Misconception: Centripetal force is a new type of force that acts on a body.

Clarification: Centripetal force is not a new type of force like gravitational force

or electrostatic force. Any center seeking force can be called as centripetal force.

Question 8.What will happen if the string to which the stone is tied is suddenly snapped? Justify

your answer from both ground’s and stone’s frame of reference.

4. Free fall, Weight and Mass

(Refer to video: Free Fall, Weight and Mass)

a. Free Fall and Acceleration due to Gravity (g)

Imagine if you drop two balls, one heavier and other lighter, both of them at the same time and

from the same height. Which would hit the ground first? Would it be the heavier one because

it weighs more? Or would they both hit the ground at the same time?

A body is said to be in free fall if the only force acting on it is the force of gravity. All bodies,

whether heavy or light, fall at the same rate near the earth’s surface; provided we neglect air

resistance. Free fall is any motion of a body where the only force acting upon it is gravity.

For a freely falling body, we can apply equations of motion to analyze its motion. A constant

acceleration acts in the downward direction (i.e. the acceleration due to gravity). Here we have

made an assumption that the body is near the Earth’s surface and air drag is negligible.

𝑣 = 𝑢 + 𝑎𝑡

𝑠 = 𝑢𝑡 +1

2𝑎𝑡2

𝑣2 = 𝑢2 + 2𝑎𝑠

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It is important to note that we will take acceleration, ′𝑎′ to be positive when it is in the direction

of the velocity and negative when it opposes the motion.

For a body near the surface of earth,

𝑚𝑔 = 𝐺𝑀𝑚

𝑟2

Or,

𝑔 =𝐺𝑀

𝑟2

This indicates that the acceleration of a freely falling body near earth’s surface does not depend

on the mass of the body. This is known as acceleration due to gravity.

Substituting 𝐺 = 6.67 × 10−11 𝑁𝑚2𝑘𝑔2, 𝑀 = 6 × 1024 𝑘𝑔 and, 𝑟 = 6400 𝑘𝑚,

we get,

𝑔 = 9.8 𝑚/𝑠2

Misconception: Heavier objects fall at a faster rate near earth’s surface.

Clarification: All objects, irrespective of their mass, fall at the same rate near

earth’s surface (provided we neglect air drag and any other resistive force).

Question 9.Two bodies A and B are dropped from two towers of heights 5 m and 10 m respectively.

Calculate the ratio of time taken by them to hit the ground.

b. Weight and Mass

Although mass and weight are somewhat related, they are not the same entity! Mass, as we

know, is a measure of inertia, i.e. the resistance that it offers to a change in its state of motion.

More the mass; more is the inertia. On the other hand, the force of attraction of the earth on an

object is known as the weight of the object.

Do You Know?

The human body can handle increased g-forces as seen in activities such

as dragster races, airplane acrobatics and space training. But if you go

beyond 4g or 5g it becomes very uncomfortable for us. The highest

known acceleration voluntarily experienced by a human is 43 g by g-

force pioneer John Stapp.

Question 10.How does mass differ from weight?

We know that the weight of a body on moon is only 1/6th of its weight on earth. The weight of

a body varies even on earth’s surface. Due to flattening of the earth at poles, a body weighs

more at the poles as compared to equator.

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Question 11.Although we say that the mass of a body is constant, it is not entirely true. Under what

circumstances will the mass of a body vary?

c. Weightlessness

While the actual weight of a body is determined by its mass and the acceleration due to gravity,

one's “effective weight” is different from actual weight. E.g. for a person standing on the floor,

the effective weight comes from the fact that he is supported by floor (here normal).

If all support is removed suddenly and the person begins to fall freely, he feels suddenly

"weightless". The state of weightlessness can be achieved in several ways, all of which involve

significant physical principles. Weightlessness occurs when uniform gravity acts solely by itself

i.e. gravity is the only force acting on the body.

E.g. you may feel weightless in an aircraft when it is accelerating downwards with an

acceleration of g.

Do You Know?

Some bacteria become nastier in space. E.g. salmonella, the bacteria

that commonly causes food poisoning, becomes three times more

virulent in microgravity, posing a major concern.

Question 12. We all enjoy roller coasters for the acceleration and weightlessness they provide.

Considering the path of a roller coaster as the segment of a circle, derive the condition for

weightlessness.

http://www.livescience.com/2629-salmonella-tricky-attack-plan-revealed.html

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IX – Std. Gravitation – Homework

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1. a) State the universal law of gravitation. Can the gravitational force between two bodies be

repulsive in nature? Justify your answer.

b) What will happen to the force of gravitation between two objects A and B if the distance

between them is doubled?

2. How is the gravitational constant defined? What is its value on earth? How is its value

different on the surface of moon?

3. State all the three Kepler’s laws.

4. What is the importance of universal law of gravitation? Why is the gravitational force

insignificant between ordinary bodies?

5. What is acceleration due to gravity? Does its value remain constant on earth’s surface?

6. Show that a body weighing 6 N on earth weighs just 1 N on the moon. Does its mass also

become one-sixth? Why or why not?

7. a) What is free fall? Write the modified equations of motion for a freely falling body.

b) Two bodies of mass 10 kg and 12 kg are falling freely. What is the acceleration produced

in the bodies due to force of gravity?

8. Differentiate between weight and mass of a body.

9. A ball is thrown vertically upwards with an initial velocity of 9.8 m/s. Calculate

a) Time taken before it reaches the ground again

b) Maximum height achieved

10. What are the similarities and differences between gravitational force, magnetic force and

electrostatic force?

11. If apple also attracts the earth according to Newton’s 2nd law, then does earth also accelerate

towards the apple? Explain why/why not?

12. A stone is dropped from the edge of the roof. It passes a window 2 m high in 0.1 s. How far is

the roof above the window? Take g = 10m/s2

13. Where do we observe the maximum value of the gravitational acceleration, at Equator? or at

Poles? or on Mt Everest top? or in a coal mine? Explain.

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IX – Std. Gravitation – Homework

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14. A particle of mass m1 is kept at x = 0 and another of mass m2 at x = d. When a third particle

is kept at x = d/4, it experiences no net gravitational force due to the two particles. Find

m2/m1.

15. How are ocean tides caused?

16. A ball is thrown with an initial velocity of 20m/s. Find the time of flight and the maximum

height reached by the body? (g= 10 m/s-2)

A) 4s, 20m

B) 5s, 25m

C) 6s, 36m

D) Can’t say

17. The weight of an object in a satellite orbiting the earth is

A) Equal to its weight on earth’s surface

B) Somewhat less than its weight on earth’s surface

C) More than its weight on earth’s surface

D) Zero

18. For a body thrown vertically upwards,

A) Time of ascent > Time of descent

B) Time of ascent < Time of descent

C) Time of ascent = Time of descent

D) Depend on the initial velocity

19. The force of gravity on a body varies slightly from place to place on the earth for two reasons.

(i) shape of earth and (ii)

A) Rotation of earth

B) Mass of earth

C) Circumference of earth

D) None of these

20. In order to derive the law of gravitation, Newton assume that the moon’s orbit is?

A) Elliptical

B) Circular

C) Parabolic

D) Regular

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ATOMIC STRUCTURE

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IX – Std. Atomic Structure – Class notes II

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1. Introduction

What is all matter made up of?

Before we get into what an atom is, and what we mean by atomic structure, look around you.

You will find buildings, lots and lots of them. Now you know that these buildings are basically

made up of bricks and cements, so we can say that the buildings are made up of bricks. But

have you ever thought about what makes up a brick?

a. Early Models of Atom

(Refer to video clip - Introduction, subtopic - Introduction)

Democritus, an ancient Greek philosopher, believed that if we keep dividing, say a

piece of bread into smaller pieces and again, divide the smaller piece into even

smaller pieces, we will reach a situation where the particle can’t be divided

anymore. Democritus named these particles Atomos (meaning indivisible).

Similar idea was declared by Maharishi Kanada of India and he named these

indivisible particles paramanu.

Aristotle dismissed these theories by saying that “seeing is believing”, and since

these atomos couldn’t be seen, Democritus’ theory was wrong.

b. Dalton’s Atomic Theory

(Refer to video clip - Introduction, subtopic - Introduction)

First scientific theory about the structure of atoms was proposed by John Dalton in

the year 1808.

Write down Dalton's Atomic Theory

Question1. Mention drawbacks of Dalton’s atomic theory.

2. Sub-Atomic Particles

The early models of atom portrayed the atom as an indivisible particle. But these models were

either hypothesis or theories that couldn’t be proved. This caused a seed of doubt to be planted.

Were these atoms really “indivisible”?

a. Discovery of Electrons

(Refer to video clip - Introduction, subtopic - Discovery of electrons)

The first person to disprove Dalton’s atomic theory was J. J. Thomson. In the year

1897, Thomson conducted an experiment inside a cathode ray tube. Thomson passed

electricity at high voltage through a gas at very low pressure. Streams of particles were

discharged from the cathode that produced luminescence on the other side of the CRT.

By conducting this experiment with various gases, he made some conclusions

What are the conclusions made by J. J. Thompson?

b. Thomson’s Model of the Atom

(Refer to video clip - Introduction, subtopic - Discovery of electrons)

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Thomson, in the year 1903, proposed a model to explain the structure of atom. Note

that at this point of time only protons and electrons had been discovered. He suggested

that the structure of atom resembled that of a plum pudding or a watermelon. The seeds

or plum were the negatively charged particles that were embedded on a positively

charged sphere (pudding or watermelon).

Figure 27 - The Plum-Pudding model

Question2. Why was the Plum-pudding model unsuccessful?

c. Discovery of Protons

It was only a matter of time before someone realized that the atom must be having some

positive particles as the atom as a whole is neutral. E. Goldstein performed a very

similar experiment to J. J. Thomson. When he passed electricity at high voltage

through a gas at low pressure, he observed that streams of heavy particles were given

out by the anode.

List down the observations made by E. Goldstein -

Question3. Why did the mass and charge of anode rays depend on the gas taken whereas the cathode

rays’ properties were independent of the gas taken?

Question4. What do you think is the difference between anode and cathode rays?

3. Radioactivity

(Refer to video clip - Radioactivity, subtopic - Radioactivity I)

Most of the elements around us are stable, but there are elements which are unstable and hence

disintegrate. The nucleus of such atoms undergoes change along with discharge of certain

particles. These particles are called alpha, beta and gamma particle. Alpha particles are

positively charged particles with a mass of 4u, beta particles are negatively charged particles

with negligible mass and gamma particles are pure radiations and hence do not carry any charge

or mass.

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Question5. Write down the properties of Alpha and beta particles.

a. Rutherford’s Gold-Foil Experiment

(Refer to video clip - Rutherford’s Model)

After the discovery of the sub-atomic particles, the first part of puzzle was solved.

Finally we knew what constituted an atom. But did we know how these sub-atomic

particles were arranged inside an atom? Rutherford was the first to answer this with the

help of his Gold-foil experiment in 1911. The setup of his experiment is shown below:

Figure 28 - Gold-Foil Experiment

Note down the observations made by Rutherford with respect to the gold foil experiment-

b. Discovery of Nucleus

(Refer to video clip - Rutherford’s Model)

In 1932, James Chadwick noticed that all the mass of an atom could not be accounted

for on the basis of only protons and electrons present in it. For example, a carbon atom

contained 6 protons and 6 electrons and should ideally have a mass of 6u. But

experiments showed that the mass of Carbon atom was 12u. What did this mean? It

meant that there were other subatomic particles which were neutral and had appreciable

mass. He named these particles as Neutrons

Did you know?

Nearly one hundred percent of the mass of an atom (99.94%) is

contained in the nucleus.

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Question6. How is a neutron different from an electron?

Question7. What are the similarities and differences in the properties of electrons and protons?

Misconception: Atom is a solid entity with definite boundaries as shown in various

figures.

Clarification:Atoms are 99.99% free space with the remaining 0.01% being the

nucleus. If the size of an atom were imagined to be a football field, the nucleus would

be equivalent to a football placed in the pitch. Also, an atom doesn’t have any definite

boundaries. Its radius is defined as the distance of the outermost shell from the

nucleus.

Rutherford’s model helped gain very important insights. It was the first to suggest the concept

of a concentrated nucleus. According to Rutherford, the mass and positive charge of the atom

was concentrated in a small portion called nucleus, located in the center of atom. Ideally,

bundling up the positive charges together should have had made the nucleus unstable, but

somehow, the nucleus managed to remain stable.

Question8. The nucleus is comprised of densely packed positively charged protons which should repel

each other. What is the force that keeps the nucleus together?

Later it was found that some elements had unstable nucleus which eventually disintegrated

giving away alpha and beta particles. After numerous experiments, the scientists were able to

obtain a relationship between elements which often disintegrated and the ratio of protons to

neutrons they had.

4. Neils Bohr’s Model

(Refer to video - Neil Bohr’s Model)

Neil Bohr went a step further with his model, in 1913.He suggested, in addition to a

concentrated nucleus, the electrons revolved around in stationary orbits. The main postulates

of his theory were:

Write down the postulates in the space given below -

According to Bohr, the atomic structure was very similar to our solar system in which the

nucleus formed the central sun with the electrons revolving around. He named these shells or

orbits as K, L, M, N, etc.

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Figure 3 - Bohr's Atomic Model

Bohr intentionally named the shells as K, L, M, etc., and not A, B, C, etc., because he wasn’t

sure if these were the only shells and hence, wanted space on either side for any future

possibilities.

In 1921, Bohr and Bury gave some laws for distribution of electrons in various orbits, which

are now called Bohr-Bury Scheme.

Main points of the Bohr-Bury scheme are:

Question9. What were the limitations of the Bohr’s atomic model?

This can be understood with the help of some examples. The electronic configuration of

Helium having 2 electrons and that of Carbon having 6 electrons are shown below.

Figure 4 - Atomic Structure of Helium Figure 5 -Atomic Structure of Carbon

Question10. Write down the electronic configuration of Lithium(3 electrons), Chlorine(17 electrons)

and Potassium(19 electrons).

Did you know? There are 254 known stable isotopes and 80 elements which have at least one stable

isotope. Twenty-six elements only have one stable isotope. These elements are called

monoisotopic.

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1. List the main postulates of Dalton’s atomic theory.

2. Complete the sentence by filling the blanks: _________ , ___________ and __________ are

the building blocks of an atom.

3. With the help of an example, explain what elements are.

4. Why are atoms electrically neutral particles?

5. Why was a gold foil preferred over lithium foil by Rutherford in his experiment?

6. Differentiate between Dalton’s atomic model and modern atomic model?

7. Tick the correct answer: The electronic configuration of Calcium is-

a. K-2, L-8, M-10 b. K-8, L-8, M-4

c. K-2, L-8, M-8, N-2 d. K-2, L-8, M-2, N-8

8. Write the electronic configuration of Magnesium as per Bohr-Bury Scheme.

9. Complete the table given below:

10. Chlorine is an element having atomic number 17. It is a mixture of two isotopes having mass

number 35 and 37.

a. What is meant by “atomic number of element”? What do you understand by an

‘isotope‘?

b. Write the electronic configuration of chlorine atom.

c. Give one property of hydrogen chloride which agrees with it being a covalent

compound.

11. Elements X, Y and Z have atomic numbers 3, 10 and 17 respectively.

a. Which element is a metal?

b. Which element is a noble gas?

c. Which element is a non-metal?

12. Explain the postulates of Bohr’s atomic model.

13. Draw the electronic configuration of argon, fluorine and magnesium.

Element Symbol No of protons No of neutrons No of electrons

Silicon 1428Si

Boron 511B

Calcium 2040Ca

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14. The transfer of one or more electrons from one atom to the other forms a (an) _______ bond.

a) Ionic b) Covalent

c) Hydrogen d) Metallic

15. Match the following

1 Cathode rays Positively charged mass at the centre of an atom

2 Atoms Positively Charged particles

3 Alpha rays Negatively charged particles

4 Nucleus Electrically neutral

16. State whether each of the following statements are True or False:

a. The outermost shell of an element is the valence shell.

b. The chemical properties of elements are decided by valence electrons.

c. Cations are good oxidizing agents.

d. Hydrogen has a proton and a neutron in its nucleus.

17. Represent the formation of a H2 molecule by electron dot diagram.

18. Consider the following elements labelled from A to E

i. Which of these elements contains 7 protons?

a) A b) E

c) D d) C

ii. Which of the given elements are metals? (Hint: Metals tend to lose their outermost electrons

to achieve a complete octet

19. Which isotope of iodine is used in the treatment of goitre?

a) 13153I b) 132

53I

c) 13155I d) 131

54I

20. Define isobars with the help of an example.

ATOMS MASS No. ATOMIC No.

A 40 20

B 19 9

C 7 3

D 16 8

E 14 7

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ATOMS AND MOLECULES

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1. Introduction

What is Chemistry?

The answer is very simple. It is the study of atoms and molecules, how they behave and interact

with each other through different types of bonds. But that’s not how it all started.

a. The Four Elements

(Refer to subtopic - Laws of Chemical Combination I& II)

Throughout man’s evolution, human beings have always tried to understand what happened

around them and how they could use it for their convenience. One of the first things that

caught their curiosity was Fire. Fire along with air, water and land were considered the

four elements that made up everything. Democritus and Maharishi Kanada independently

believed that if we kept on breaking any substance into smaller and smaller particles, we

would eventually get an indivisible particle called “atomos” and “paramanu” respectively.

But these definitions were insufficient to understand what occurs around us.

Question1. Describe the experiment Lavoisier conducted and how it led to the discovery of Law of

conservation of mass? (Refer to subtopic - Laws of Chemical Combination III)

b. Elements and Compounds

(Refer to subtopic - Laws of Chemical Combination IV)

With John Dalton’s atomic theory, the definition of element changed. Elements were now

considered to be made up of atoms. These atoms were identical for an element and when

these atoms of one element combined with atoms of other elements, compounds were

formed. But Dalton’s theory had its limitations. One huge limitation was that his theory

considered atoms to be indivisible but soon discovery of electrons, followed by discovery

of protons and neutrons proved him wrong.

Question2. Discuss the pros and cons of Dalton’s atomic theory.

2. Atomic Mass

(Refer to video clip - Atomic Mass)

After various experiments and atomic models, it was established that the structure of atom

looked somewhat similar to our solar system. Most of the mass was concentrated in the centre

in a region of tightly packed positive and neutral particles called Nucleus.

What do you understand by atomic mass?

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Figure 29 - Structure of Atom

Mendeleev considered atomic mass for arranging the known elements and found striking

similarities among the elements in a group. Mendeleev used Hydrogen as a standard for

measuring the relative weights of the known elements as Hydrogen was the lightest known

element. Even Oxygen was once considered as a standard for measuring weights because of its

ability to bond with other elements. But this was soon replaced by Carbon atom (Carbon-12

isotope).

Figure 30 - Mendeleev's Periodic Table

Question3. What do you mean by Carbon-12 isotope and why was it used as a standard for measuring

relative weights?

1/12th mass of a Carbon-12 isotope was considered 1 a.m.u where a.m.u stood for atomic mass

unit. Oxygen atom being 4/3 times heavier than a Carbon atom had a mass of 16 a.m.u in the

above system. Hydrogen being 1/12 times lighter than Carbon was the lightest element having

atomic mass of 1 a.m.u.

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3. Mole Concept

(Refer to video clip- Mole Concept)

Question4. How is a molecule different from an atom? What will be the mass of 1 molecule of

Hydrogen?

In 1811, an Italian chemist Amedeo Avogadro came up with a theory after being inspired by

Gay-Lussac’s Law of combining volumes. According to Avogadro’s Law,"equal volumes of

gases at the same temperature and pressure contain the same number of molecules regardless

of their chemical nature and physical properties". He measured the mass of a 22.4 L sample of

Hydrogen and divided that by the mass of an individual Hydrogen molecule. He considered

22.4 L of Hydrogen as 1 mole and concluded that 1 mole of any elementcontained 6.022 x 1023

particles. As the mass of 1 molecule of Hydrogen was 2 a.m.u., 1 mole of Hydrogen molecules

weighed 2 grams where 2 grams was the gram molecular weight of Hydrogen.

Question5. State Gay-Lussac’s Law of combining volumes.

Mole is simply a unit for representing the number of atomic and subatomic particles in a sample,

just like score is a unit which represents a quantity of 20. 1 mole of any substance will have

6.022 x 1023 particles (a.k.a. Avogadro’s number). Some places have 6.023 x 1023 particles as

1 mole because it is easier to remember and the difference is insignificant.

Question6. A sample X has 3.011 x 1021 particles contained in it. Calculate the no. of moles of X in the

sample.

Question7. Calculate the number of atoms in 2.5 moles of Ammonia gas (NH3) taken in a closed beaker.

Question8. Calculate the number of electrons in a sample of Nitrogen gas (N2) which weighs 5.6 grams.

(Gram Molecular Mass of Nitrogen is 28gm)

Did you know?

While calculating the atomic mass of any element, we ignore the mass of electrons

present in it because an electron is 1/1836 times lighter than a proton and hence, its

contribution to the total mass of atom is negligible

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IX – Std. Atoms and Molecules – Class notes II

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4. Relation between mole, mass and volume.

(Refer to video clip - Mole and Mass)

The Avogadro’s number is the number of molecules that are contained in a sample of 22.4 L of a

gas at NTP. Since, according to Avogadro’s Law, equal volume of gases should contain equal

number of particles at the same temperature and pressure, we can look at mole concept from two

directions. Firstly, a mole has 6.022 x 1023 particles. So any sample having 6.022 x 1023 molecules

will be considered 1 mole. The other approach is to calculate mole according to the volume present.

1 mole of any gas will have 6.022 x 1023 molecules and since these many particles occupy 22.4 L

at STP, hence, any gas occupying 22.4 L at NTP will be considered as 1 mole.

Figure 3 - Relationship between Mole, Mass and Volume

Some useful formulae:

Mole = Weight of Sample

Molecular Mass Mole =

Volume of Sample at NTP

22.4 L

Mole = No.of particles

6.023 x 1023

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Question9. Express 6.4 gm of O2 gas in terms of its equivalent volume and number of molecules.

Question10. Metal X reacts with dilute acid, releasing 7.72 L of a gas at NTP which reignites the splint

with a pop sound. Calculate the number of molecules of the gas produced.

Question11. 0.3 gm of H2 gas reacts with N2 gas to produce Ammonia according to the following

reaction: N2 + 3H2→ 2NH3.Calculate the volume of Ammonia released at NTP.

5. Atomic Valency

(Refer to subtopic - Atomic Valency III)

Define the term ‘Valency’.

If we move from left to right in 2nd period of the modern periodic table, we will observe that

the number of valence electrons increases from 1 to 8. Lithium has 1 valence electron,

Beryllium has 2, Fluorine has 7 and Neon has 8. So the valency varies from 1 to 8.

Question12. Show the valency of Sodium, Aluminium and Oxygen with the help of shell diagrams.

All atoms participate in reactions to achieve the electronic configuration of the nearest noble

gases and attain stability. These noble gases have maximum number of electrons that their

outer-most shell can accommodate and are hence, largely unreactive.

Figure 4 - Atomic Structure of Noble Gases

Did you know?

Valency is a measure of the combining capacity. Even though a Chlorine atom has

7 electrons in its valence shell, it only shares 1 of them in a covalent bond. Many

elements also show multiple different valencies in different compounds such as

Iron, Tin, Lead and Phosphorus.

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a. Cations

(Refer subtopic- Atomic Valency III)

Ionic bonding proceeds with actual

transfer of electrons. When an atom

loses an electron, at that instant, the

number of protons is greater than the

number of electrons by 1. Hence, it

attains a positive charge and is now

called a Cation.

Figure 5: Formation of Sodium ion

b. Anion

(Refer subtopic- Atomic Valency III)

When a neutral atom accepts an electron during an ionic bond formation, it becomes

negatively charged because it has more number of electrons as compared to protons. These

negatively charged ions are called Anions. These anions combine with the cations leading

to the formation of ionic bonds. These bonds are held together by strong electrostatic forces.

Question13. With the help of diagrams, show how ionic bond is formed between Sodium and Chlorine.

c. Atomicity

Define atomicity.

Question14. What will be the atomicity of the following elements/compounds?

(i) Ammonia (ii) Ozone (iii) Methane (iv) Chlorine

6. Writing Chemical Formula

(Refer video clip - Writing Chemical Formula)

Chemical formula of an element/compound represents the ratio in which the atoms exist in a

molecule. The chemical formula of any element/compound can be written in the following

steps.

The name of more electropositive element (usually a metal) is written first

The name of more electronegative is written in the last with the name ending as –ide.

For e.g. Chloride, bromide, etc.

The valency of the electropositive element/ion should satisfy the valency of the

electronegative element/ion.

There should be no common factor in the atomicity of electronegative and

electropositive elements in the molecule.

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Question15. Write the chemical formula of a compound compromising of:

(i) Carbon and Oxygen (ii) Nitrogen and Hydrogen (iii) Magnesium and

Chlorine.

Alternate Method

(Refer subtopic - Writing Chemical Formulae II)

Write the more electropositive element first and then the electronegative element.

Write their respective valency below them.

Cross multiply their valencies to get the atomicity.

Cancel out any common factor in the obtained atomicities.

Question16. Write the chemical formula of the following compounds using the alternate method:

(i) Lithium and Oxygen (ii) Chlorine and Fluorine (iii) Carbon and Iodine

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1. State whether True or False:

An atom is the smallest particle of an element that exhibits all the properties of that element.

2. In a reaction, 15.3 g of sodium carbonate reacted with 16 g of ethanoic acid. The products

were 12.2 g of carbon dioxide, 1 g water and 18.1 g of sodium ethanoate. Show that these

observations are in agreement with the law of conservation of mass.

Sodium carbonate + ethanoic acid sodium ethanoate + carbon dioxide + water

3. Write down the 5 postulates of Dalton’s atomic theory.

4. Give the Latin names and symbols for the following elements:

Sodium

Potassium

Mercury

5. Calculate the relative molecular mass of caustic soda.

6. Give the relationship between 1 mole of any particle with Avogadro’s number and volume.

7. Which postulate of Dalton’s theory satisfies the law of constant proposition?

8. Convert the following into moles.

a) 20 g of oxygen

b) 50 g of water

9. Give the chemical formula of the following compounds:

a) Magnesium sulphate

b) Aluminium oxide

c) Caustic soda

10. With the help of an example, explain polyatomic ions.

11. How many atoms are present in a:

a) Sulphite ion

b) Hydrogen carbonate ion

12. Write down the rules to be followed while naming an ionic chemical compound.

13. Write three differences between anions and cations.

14. What are the drawbacks of Dalton’s atomic theory?

15. Define atomicity. What is the atomicity of the following compounds?

a) Sulphur

b) Phosphorus

16. Which of the following is not a symbol of an element?

a) Ne b) So

c) Au d) N

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17. Chemical formula of ammonium sulphate is:

a) (NH4)2SO2 b) (NH3)2SO2

c) (NH4)2SO4 d) (NH4)3SO5

18. Avogadro number is defined as the number of atoms in a 12 g sample of __________

element.

a) Carbon- 12 b) Carbon

c) Oxygen d) Hydrogen

19. Latin name of tungsten is-

a) Ferrum b) Kalium

c) Hydrargyrum d) Wolfram

20. The relative mass of a molecule is expressed as:

a) Atomic mass unit b) Atomic weight unit

c) Relative atomic mass unit d) None of these

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IS MATTER AROUND US PURE?

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IX – Std. Is the matter around us pure? – Class notes

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1. Introduction

Physically, matter can be classified into three physical states. The physical aspects cover these

states, their inter conversion and the changes it undergoes while transforming. But matter can

also be classified by its chemical composition as:

Pure substance

Impure substance

2. Pure substance (Purity)

(Refer to video clip - Purity)

What do you understand by the term 'Pure Substance'?

Question1.Is the pure milk that you get, really pure? Justify your answer.

Pure substance can be further classified into:

a. Elements

(Refer to video clip - Elements)

Define the term 'elements'.

b. Compounds

(Refer to video clip - Compounds)

Question2.Why is water considered as a compound?

Figure 31 - Types of Pure Substances

Very few of the chemicals and substances we encounter on daily basis are in their pure form.

Most of them are mixtures.

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3. Impure Substance

(Refer to video clip - Mixtures)

A mixture is a combination of two or more pure substance in which each pure substance retains

its individual chemical properties. Mixture can be composed of solid, liquids or gases.

What are the two basic types of mixtures?

a. Homogenous mixture

A homogeneous mixture is simply any mixture that has uniform composition throughout

the mixture.

There is only one phase of matter observed in a homogenous mixture. Mixtures where the

observed phase is liquid are known as True solutions or generally as Solutions.

Question3.You have one glass of water and some sugar and sand. How will you create a homogeneous

mixture?

b. Solutions

(Refer to video clip - Solutions)

A homogeneous mixture of two or more substances, which may be solids, liquids, gases

or any other combination of these.

The particles should have dimension between 0 and 2 nanometer.

Solutions are transparent, i.e. light can pass through it. Mixtures are stable and do not

change after standing for long time.

Question4.Mention the solute and solvent of a water-salt solution.

c. Heterogeneous mixture

A heterogeneous mixture is one that is composed of components that aren’t uniform.

Instead, they have localized regions where they have different properties.

i. Colloids

(Refer to video - Colloids)

What are colloids?

Types of colloids

Question5. Can you name two colloidal solutions which have gas as dispersion medium and liquid and

solid as dispersed phases?

Dispersion Medium Dispersed Phase Type of Colloid Example

Solid Solid Solid sol Ruby glass

Solid Liquid Solid emulsion/gel Pearl, cheese

Solid Gas Solid foam Lava, pumice

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Question6. What are sols and emulsion?

ii. Suspensions

(Refer to video clip - Suspensions)

A suspension is a heterogeneous mixture in which solids are dispersed in liquids. The

solute particles in suspension do not dissolve but remain suspended throughout the

medium.

Question7.Write the properties of suspension.

4. Concentrations

(Refer to video clip - Concentration of Solutions)

A complete description of a solution, it describes what the solute is and how much solute is

dissolved in a given amount of solvent or solution. The quantitative relationship between solute

and solvent is the concentration of the solution. This concentration may be expressed using

several different methods.

Question8.How do you express concentration of a solute in solvent in terms of percentage?

5. Physical and Chemical Changes

(Refer to video clip - Physical Vs Chemical changes)

Now we have studied both the chemical and physical states of matter. There are several

differences between the physical & chemical changes.

a. Physical Change

Changes wherein the molecule does not change its chemical makeup but its physical

appearance might be altered.

Did you know?

We all have experienced such a picture where we are

able to see the path of light. Such a phenomenon occurs

when light travels through a colloid. This

phenomenon, known as Tyndall effect, is caused by

light scattering by particles in a colloid or particles in

a very fine suspension.

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Figure 2 - Heat Leading to Larger Inter-molecular Space.

b. Chemical Change

Question9. Would you term curd formation as a chemical change? Justify your answer.

Question10. Classify the following on the basis of whether they are a chemical or physical change.

(a) Whipping of egg whites (b) Milk souring (c) Dicing the potato

6. Separation Techniques

(Refer to video clip - Introduction to Separation)

Heterogeneous and Homogeneous mixtures are separated using different techniques based on

the type of mixture we are dealing with.

a. Sublimation

(Refer to video clip - Sublimation)

Sublimation is a process of conversion of a solid into vapour or a vapour back to solid state,

without passing through the liquid state.

Did you know?

One of earliest separating techniques was invented by

farmers who separated husk from paddy. They allowed

both of them to fall along the wind. Husk being lighter,

was carried by the wind to a longer distance.

Did you know?

One of earliest separating techniques was

invented by farmers who separated husk

from paddy. They allowed both of them to

fall along the wind. Husk being lighter, was

carried by the wind to a longer distance.

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Figure 3 - Separation using Sublimation

Question11. What type of mixture can be separated by sublimation?

b. Distillation

(Refer to video clip - Distillation)

What is distillation? Which property of substances does this process use as a basis for

separation of components of a mixture?

Figure 4 - Separation by Distillation

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c. Centrifugation

(Refer to video clip - Centrifugation)

Question12. Explain the method of centrifugation.

Any heterogeneous mixture containing an insoluble solid in a liquid can be separated by two methods

Sedimentation

Decantation

d. Sedimentation

The insoluble solid substance in the solution settles down at the bottom of beaker and a

clear liquid is obtained standing above the solute. This process is called sedimentation.

Figure 5 - Settling of Solute : Sedimentation

Question13. What do you understand by the process of decantation?

e. Chromatography

(Refer to video clip - Chromatography)

Define chromatography. Explain the underlying principle involved.

Figure 6 - Separation of Dyes

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Misconception: Passing any water through a water-purifier makes it fit to drink.

Clarification: Water purifiers have special filters that keep back dust and impurities

present as particles in the solution. But these water purifiers are unable to keep out any

impurities that might be dissolved in the water. Speaking in simple terms, water

purifier only purifies the water physically, leaving scope of chemical poisoning.

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1. What do you mean by a pure substance?

2. Are compounds pure substances? Justify your answer.

3. What do you mean by a heterogeneous mixture?

4. In a homogeneous solution, the dimension of solute particles varies between:

a. 1 – 103 nm b. 104 - 106 nm

c. 105 - 106 nm d. 108 – 109 nm

5. Does light pass through a colloid without any deflection?

6. How is a suspension different from a colloid?

7. Is milk a colloid, suspension or true solution? Justify.

8. How will you separate a mixture of iron fillings and sand?

9. What is sublimation? Give examples of sublimable substances.

10. Explain the principle of distillation which is used as a separation method.

11. Explain the working of centrifugation separation technique? Use the example of separation of the

components of blood.

12. What type of mixtures can be separated by sedimentation?

13. What do you mean by decantation?

14. A solution of water and sugar is an example of:

a. Colloid b. Suspension

c. True solution d. Pure substance

15. Mixtures of coloured compounds can be separated by:

a. Distillation b. Decantation

c. Centrifugation d. Chromatography

16. What is the use of chromatography? Explain the principle behind it.

17. Light passes through _________ without any deflection.

a. Solution b. Colloid

c. Suspension d. Emulsions

18. What is meant by concentration of solution?

19. How will you separate a solution of oil and water?

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20. You have two substances with a large difference in their weight. Which of the following technique

is used for the separation of the mixture?

a. Distillation b. Chromatography

c. Sublimation d. Centrifugation

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MATTER IN OUR

SURROUNDINGS

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IX – Std. Matter in our surroundings – Class notes I

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At the end of this session, you will have your notes ready. (Depends accordingly)

1. Introduction

(Refer to video clip - Physical nature of matter)

What is matter? There are many possible definitions for matter.

Matter is anything that has mass and takes up space.

Matter is everything around you.

The substance of which any physical object is composed.

Question1. What do you understand by mass?

a. Nature of Particles

(Refer to video clip- Characteristics of particles of matter)

Write down the four points regarding the nature of particles.

2. States of Matter

(Refer to video clip - States of Matter)

Matter exists in three states that are distinguished by the strength of the bonds holding the

molecules of matter together.

Figure 32 - The Three States of Matter

Can you recognize three states of matter given above?

3. Inter-convertibility of Matter

(Refer to video clip - Can matter change its state)

Kinetic theory of matter explains the difference between these three states of matter.

Solids can transform into liquids & liquids into gases. Many factors contribute to the inter-

conversion of states of matter.

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Figure 33 - Inter-conversion of States of Matter

The kinetic theory of matter states that matter is composed of a large number of small particles

that are in constant motion. It also assumes that particles are small and widely spread. They

collide and exchange energy. The theory helps explain the flow or transfer of heat and the

relationship between temperature and volume of gases.

Question2. Write a brief note on the relation of kinetic energy of particles with the states of matter.

a. Solids

(Refer to subtopic - Three states, video clip - States of matter)

Particles in solid are closely packed. Inter-particle space is negligible. The

transformation of solid to liquid state by the absorption of heat at a particular

temperature and atmospheric pressure is called melting.

Figure 34 - Solid-Liquid Inter-conversion

Did you know?

It has been established that matter can exist in five states of matter. Apart

from solid, liquid and gases, matter can also exist in plasma state (hot

ionized gas) and in BEC (Bose-Einstein Condensate) state where matter is

really slow moving and extremely condensed.

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What do you understand by the term 'latent heat of fusion'?

Sublimation is the process where a solid directly transforms to gaseous state, thus

skipping the liquid state. Very few substances are sublimable.

Question3. Why do phenolphthalein balls become smaller when kept out in the open?

b. Liquids

(Refer to subtopic - The Liquid State, video clip - States of matter)

Define the term 'latent heat of vaporization'.

i. Evaporation

(Refer to video clip- Evaporation)

Evaporation on the other hand is a surface phenomenon.

Evaporation doesn’t occur at a specific temperature but

its a continuous phenomenon that occurs all the time.

Higher the temperature, more particles will come to the

surface with sufficient energy leading to greater

evaporation.

Figure 35 - Evaporation

ii. Condensation

Condensation too is a surface phenomenon and is the reverse of evaporation.

When gaseous particles lose energy and come close to the surface of liquid,

they are pulled back into the liquid surface and are said to be condensed.

a

Question4. Why does evaporation cause cooling effect? (Refer video: Evaporation)

c. Gases (Refer to subtopic- The Gaseous state, video clip- States of matter)

When gases change state, i.e. transform from gaseous to liquid state at a particular

temperature, it is called liquefaction. At this temperature, the pressure above the liquid

surface becomes equal to the atmospheric pressure.

Did You Know?

It is sometimes said that glass in very old churches is thicker at the bottom

than at the top because glass is a liquid, and so over several centuries it has

flowed towards the bottom. But, glass is neither a crystalline solid nor a

super-cooled liquid. It is an amorphous solid.

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Figure 36 - Liquid-vapor Inter-conversion

Question5. Why do you observe small water droplets forming on cold surfaces which are exposed to

air?

4. Law of Conservation of Mass

Question6. Explain the law of conservation of mass.

Misconception: The mass of reactants before a reaction is always equal to the mass of

the products after the reaction.

Clarification: Law of conservation of mass holds true only for closed systems. In case,

any of the reactant or product is allowed to leave the system law of conservation of

mass stands violated.

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1. What are the three states of matter? Can they co-exist?

2. Compare the properties of the different states of matter.

3. What do you understand by the term boiling point?

4. Is evaporation a surface phenomenon? Justify.

5. How is evaporation different from boiling?

6. Define condensation.

7. Explain the working principle behind the functional advantage of a pressure cooker.

8. Condensation occurs at a fixed temperature whereas melting occurs over a range of temperature.

(True/False). Justify your answer.

9. The particles of a solid possess:

a. Translatory motion b. Vibrational motion

c. Rotational motion d. No motion

10. _______ state(s) has definite mass but no definite volume:

a. Solid b. Liquid

c. Gas d. Liquid and gas

11. What do you mean by sublimation?

12. Why do we experience a burning sensation when we come in contact with steam?

13. Define latent heat of fusion and vaporization.

14. Sweating results in cooling of the body. Give reason.

15. State the law of conservation of mass.

16. Shrinking of naphthalene balls on prolonged exposure to air is due to:

a. Evaporation b. Condensation

c. Sublimation d. None of these

17. Distinguish between gas and vapour.

18. Explain the conversion of solid to liquid on the basis of kinetic theory of matter.

19. The phenomenon responsible for rainfall is (are):

a. Evaporation b. Condensation

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c. Both of these d. None of these

20. According to kinetic theory of matter, particles of _______ have the least amount of energy.

a. Solid b. Liquid

b. Gas d. Gas and solid

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CELL: THE

FUNDAMENTAL UNIT

OF LIFE

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IX – Std. Cell: The Fundamental Unit of Life – Class notes I

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1. Introduction to cells

Cells are the smallest unit of life that can replicate independently, and are often called the

‘building blocks of life’. The study of cells is called cell biology. Cells consist of a protoplasm

enclosed within a membrane, which contains many biomolecules such as proteins and nucleic

acids.

Question1. Cell is the structural and functional unit of life. Why do you think is it called so?

Cells can be of different shapes and sizes. To understand this, consider below given diagram

of cells found in humans.

Figure 37: A. Nerve cell B. Ovum C. Sperm D. Cheek cells

Question2. Why do cells have different shapes and sizes?

(Refer video: Introduction to Fundamental Unit of Life _ Basic Unit of Life)

a. Discovery of cell

Question3. Match the following:

Robert Hooke All animals are made up of cells

Anton Van Leeuwenhoek Discovered cell

Matthias Schleiden Invented microscope

Theodor Schwann All plants are made up of cells

(Refer video: Introduction to Fundamental Unit of Life _ Discovery of Cell)

2. Stuctural Organisation of the Cell

If we study a cell under microscope, we would come across three features in almost every cell

: plasma membrane, nucleus and cytoplasm . Let us discuss each one of them in detail.

a. Plasma Membrane

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The outer most covering of cell is called plasma membrane. The most accepted theory of

plasma membrane structure is _____________________. According to this theory, the

plasma membrane that surrounds cell has two layers (a bilayer) of phospholipids (fats with

phosphorous attached), which is fluid at body temperature. Proteins and substances such as

cholesterol become embedded in the bilayer, giving the membrane mosaic mosaic like look.

Plasma membrane separates the contents of the cell from its external environment. Plasma

membrane is a _______________ membrane i.e., it allows entry and exit of only selected

material in and out of the cell.

Question4. Explain how the fragrance of an incense stick burning in a corner of the room can be felt

throughout the room. Define the process involved.

(i) Passive Transport

This is the process of transport of materials, in and out of the cell, along a concentration

gradient without spending _________. Substances like CO2 and O2 move in and out

of the cell passively by the process of __________. The amount of CO2 present in the

extracellular fluid is less as compared to the amount of CO2 present inside the cell (CO2

is released during cellular processes). The moment this concentration gradient is

created, CO2 moves out of the cell. Similarly, when the amount of O2 present in the

extracellular fluid is more as compared to the amount of O2 present inside the cell, (O2

is utilised during cellular processes) O2 moves into the cell.

Movement of water also obeys the law of diffusion but in a special way. Movement of

water molecule from a region (solution) of its higher concentration to a region

(solution) of its lower concentration through a semi permeable membrane is known as

_________. Thus, we can say that __________ is a special kind of diffusion in which

solution moves across the gradient.

Question5. Differentiate between diffusion and osmosis.

From the above discussion, it is clear that two solutions are required for osmosis. In case

of cells, first solution is the cell sap and second solution is the extracellular fluid. When the

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concentration of extracellular fluid is more than the concentration of cell sap it is called

___________solution. When the concentration of extracellular fluid is less than the

concentration of cell sap it is called _____________solution. When the concentration of

extracellular fluid is equal to the concentration of cell sap it is called ___________ solution.

Question6. With the help of an arrow show the net movement of water when a cell is kept in the

following conditions/solutions.

Question7. Discuss the effects when a plant cell is kept in hypotonic and hypertonic solution.

Question8. What will happen if a fresh water fish is kept in sea water and why?

Did you know ?

The direction of osmosis can be reversed by applying external pressure to it.

This process is called reverse osmosis and is working principle of RO water purifiers.

(ii) Active Transport

Transport of substances in and out of cell at the expense of energy in the form of

_______ molecule is called active transport. This generally occurs when transport of

molecules across cell membrane is done against concentration gradient.

(Refer video: Fluid Mosaic Model)

b. Cell wall

In plants, other then plasma membrane, one more external layer is found called the cell

wall. Plant cell wall is made of _________. It is somewhat rigid but permeable to most of

the substances. Cell wall is also found in cells of bacteria and fungi. It provides rigidity to

the cell. It prevents the plant cells from desiccation. It gives shape to the plant cell. It

protects the plant cell from external environment (hypotonic solution).

(Refer video: Structural Organisation of the Cell_Structre of Cell)

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c. Cytoplasm

Cytoplasm is a thick matrix that fills each cell and is enclosed by the cell membrane. It is

mainly composed of water, salts, and proteins. In eukaryotic cells, the cytoplasm includes

all of the material inside the cell and outside of the nucleus.

d. Nucleus

Remember the central circle in the human cheek cell that we had seen in the beginning of

this chapter? It is the nucleus of the cell. Nucleus is the main ___________ unit of the cell.

The membrane around nuleus is called nuclear membrane which is double layered. Nuclear

membrane has pores called ____________ that help in transportation of substances in and

out of nucleus. The matrix inside nucleus is known as ____________. The nucleus contains

chromosomes, which are visible as rod-shaped structures only when the cell is about to

divide. Chromosomes contain information for inheritance of features from parents to next

generation in the form of DNA (Deoxyribonucleic acid) molecules. Chromosomes are

composed of DNA and protein. Functional segments of DNA are called _______. There

are 23 pairs of chromosomes present in the human cells.

Figure 2: A. Prokaryotic cell B. Eukaryotic cell

Did you know ? Each human cell contains around 6 feet of DNA which is tightly

packed, but very organized with proteins

(Refer video: Cell Organelles_Cytoplasm)

Cells can be divided into two groups on the basis of the type of nucleus found in them –

___________ or __________. In organisms like bacteria, nuclear membrane is absent.

Such an undefined nuclear area is called a ___________. In contrast to this, cells in which

a well defined nucleus with a nuclear membrane is present are called eukaryotic cells.

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Question9. Differentiate between prokaryotic and eukaryotic cells with an example of each.

(Refer video: Structural Organisation of the Cell_Classification of cell)

3. Cell Organelles

Eukaryotic cells contain many membrane-bound organelles. An organelle is an organized and

specialized structure within a living cell. The organelles include the nucleus, endoplasmic

reticulum, golgi apparatus, vacuoles, lysosomes, mitochondria, etc.

a. Endoplasmic Reticulum (ER)

The endoplasmic reticulum is a network of membranous tubules within the cytoplasm of

an eukaryotic cell, continuous with the nuclear membrane. There are two types of ER –

rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER). RER has

__________ attached on its surface and is involved in protein synthesis. As the name

suggests the SER has no ribosomes attached to it and is involved in _______ synthesis. In

liver cells of vertebrates, SER plays a vital role in detoxifying many poisons and drugs.

Figure 3: Endoplasmic reticulum

Question10. What do you mean by membrane biogenegis?

(Refer video: Cell Organelles_Endoplasmic Reticulum)

b. Golgi Apparatus

Golgi complex was discovered by Camillo Golgi for which he received Nobel prize in the

year 1906. It is composed of many sac-like structures which are stacked one above another.

Its functions include the storage, modification and ___________ of products made by ER

in vesicles.

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Figure 4: Golgi complex

c. Lysosomes

Lysosomes are single layered. It is _____________ system of the cell. Lysosomes help to

keep the cell clean by digesting any foreign material as well as worn-out cell organelles.

They contain powerful digestive enzymes capable of breaking down all organic material.

Question11. Explain how lysosomes help in defence of the cell.

Question12. Why lysosomes are called suicide bags of cell?

(Refer video: Cell Organelles_Golgi Apparatus and Lysosomes)

d. Mitochondria

Mitochondria is also known as ‘_____________’ of a cell as it is the site of production of

energy currency of the cell i.e. ATP. Mitochondria have two membrane coverings instead

of just one. The outer membrane is very porous while the inner membrane is extensively

folded. Each fold is called a ________. These folds provide large surface area for

generating ATP. A very unique feature of this organelle is that it has its own DNA.

Figure 5: Mitochondria

(Refer video: Cell Organelles_Mitochondria)

e. Plastids

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Plastids are major organelles found in the cells of plants and algae. Plastids often contain

pigments (chlorophyll) used in photosynthesis, and the types of pigments present can

change or determine the cell's color.

Plastids are also double layered and like

mitochondria they contain their own DNA and

ribosomes.

Question13. Match the following

i. Leucoplast a. gives colour to plant parts

ii. Chromoplast b. helps in photosynthesis

iii. Chloroplast c. colourless and stores starch, oil, protein.

f. Vacuoles:

Vacuoles are storage sacs. Vacuoles are small in size in animal cells while plant cells have

very ________ vacuoles. In plant cells vacuoles are full of cell sap and provide __________

and rigidity to the cell.

(Refer video: Cell Organelles_Plant Cell)

Question14. Based on the entire discussion and the figure given below, differentiate between plant

and animal cell.

(Refer video: Cell Organelles_Animal vs Plant Cell)

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IX – Std. Cell: The Fundamental Unit of Life – Homework

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1. Which of the following has single membrane?

A. Nucleus

B. Mitochondria

C. Chloroplast

D. Lysosome

2. The outer most layer of human cheek cell is:

A. Cytoplasm

B. Plasma membrane

C. Cell wall

D. Nuclear membrane

3. The organelle which is absent in kidney cells is:

A. Centrioles

B. Plasma membrane

C. Mitochondria

D. Chloroplast

4. Which of the following is wrongly matched?

A. Chloroplast – chlorophyll

B. Elaioplast – starch

C. Amyloplasts - carbohydrates

D. None of these

5. State whether the following statements are true or false. If false write the correct statement.

i. Amoeba is a multicellular organism.

ii. All kinds of plastids have coloured pigments.

iii. Plasma membrane is present in all cells.

iv. Movement of molecules from area of low concentration to an area of high concentration

is called diffusion.

v. Cell wall of the plant cell is a living structure.

6. Name and define the phenomenon by which raisins placed in water swells

7. A drop of ink is put gently inside a glass of water. What will be observed after sometime?

8. What change in size will be observed if a shelled raw egg and a deshelled boiled egg is placed

in water?

9. Define cell organelle with one example.

10. How does water travel across plasma membrane? Explain its movement when the cell is placed

in hypertonic, hypotonic and isotonic solution.

11. How are carbon dioxide and oxygen transported across plasma membrane?

12. Give two functions of cell wall.

13. Explain the structure of nucleus. Also mention its functions.

14. Differentiate between prokaryotes and eukaryotes with example.

15. Differentiate between rough endoplasmic reticulum and smooth endoplasmic reticulum.

16. ‘Lysosomes are suicide bags of the cell’. Justify.

17. Name the different types of plastids found in cell and mention the function of each.

18. Differentiate between plant and animal cell on the basis of presence or absence of the following:

i. Plastids

ii. Vacuoles

iii. Centrosome and centrioles

iv. Cell wall

19. Name two organelles that contain their own genetic matter.

20. Perform the following activity. Cut a potato into a cube. Carve out a small cup in the cube. Put

normal water into the potato cup. Place the potato cup in salt water. After few minutes measure

the level of water present in the cup. Give reason for your observation.

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TISSUES

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IX – Std. Tissues – Class notes

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Question 1. We know that cells are the structural and functional unit of life. What is the next level of

the hierarchy of classification? Why do we need it?

1. Introduction

Tissues are a group of cells that are specialized to perform a specific function. They are like

families of cells functioning together. Several tissues together combine to form an organ.

Tissues are different for plants and animals because their cellular structures are fundamentally

different. This results in different growth pattern in both plants and animals. Moreover, plants

and animals differ functionally as well. For instance, plants are stationary and perform

photosynthesis for manufacture of food; whereas, animals are mobile and depend on plants or

other animals for food.

(Refer video: Introduction)

2. Plant Tissues

Plant tissues can broadly be divided into two types – Meristematic tissues and Permanent

tissues.

a. Meristematic tissues

Plants grow at very specific regions. This growth is brought about by the meristematic

tissues. The cells of these tissues keep on dividing and give rise to new cells. These cells are

very active with dense cytoplasm, thin cell wall, prominent nuclei and no vacuoles.

Meristematic tissues are present at the growing parts of plant. These are dividing tissues

classified into apical meristem, lateral meristem and intercalary meristem.

(Refer video: Plant Tissues_Types of Plant Tissues)

(i) Apical Meristem

These tissues are present at the tip of shoot and root of the plant. They therefore, bring

about the increase in plant height and also the length of the root inside the soil.

(Refer video: Plant Tissues_Apical Meristem)

(ii) Lateral Meristem

These tissues are present in the lateral walls of the stems and bring in the increase in

girth of the plant.

(Refer video: Plant Tissues_Lateral Meristem)

(iii) Intercalary Meristem

These tissues are present at the base of leaves or internodes.

(Refer video: Plant Tissues_Intercalary Meristem)

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Question 2. In the given diagram, locate the position of the different types of meristematic tissues in

plants.

Question 3. Why do meristematic tissues lack vacuoles?

b. Permanent Tissues

These are the tissues which are made up of cells that lose the ability to divide and take up a

specific function in the plant. This process in which the cells of meristematic tissue take up

specific functions or roles is known as differentiation. These tissues can be broadly divided into

two types – simple permanent tissues and complex permanent tissues. Simple permanent tissue

is further divided into three types – parenchyma, collenchyma and sclerenchyma. Similarly,

complex permanent tissue is further divided into two types – Xylem and Phloem.

(Refer video: Plant Tissues_Permanent Tissues)

(i) Simple permanent tissues

As already discussed, these tissues are of three different types. Parenchyma tissues are

made up of loosely packed cells with thin cell walls and large intercellular spaces. They

are live cells and help in support and storage. If the parenchyma cells contain

chlorophyll, they are called chlorenchyma and if they consists of large air spaces, they

are called aerenchyma.

(Refer video: Plant Tissues_Parenchyma)

Collenchyma tissues are made up of live cells which have irregularly thickened corners

with thus decreased intercellular spaces. They help in bending of various parts of the

plant without breaking.

Sclerenchyma tissues make up the hard and stiff parts of the plant. They are made up

of dead, long and narrow cells. They almost have no intercellular space as the walls are

thickened due to the presence of lignin.

(Refer video: Plant Tissues_Collenchyma)

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Question 4. Identify the types of tissues and give one structural feature of each.

(ii) Complex Permanent Tissues

Complex tissues are made up of many types of specialized cells coordinating to perform a single

function. As we have already learnt, these are of two types – xylem and phloem. These form

the vascular system of the plant. Vascular or conductive tissues transport food, nutrients and

water across the plant. Water and minerals are conducted by xylem tissue while food is

conducted by phloem tissue.

Xylem is made up of the following components – vessels, tracheids, xylem parenchyma and

xylem fibres. Of all the components, the vessels and tracheids help in conduction of water and

minerals from the soil. Xylem parenchyma help in food storage and the xylem fibres provide

mechanical support.

Question 5. Identify the xylem components in the following figure.

(Refer video: Plant Tissues_Complex Tissue - Xylem)

Phloem is made up of the following components – sieve tubes, companion cells, phloem parenchyma

and phloem fibres. Unlike xylem, phloem conducts in both directions. Among all the components,

phloem fibres are the only dead cells.

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Question6. Name the tissue and label its parts in the following diagram.

(Refer video: Plant Tissues_Complex Tissue - Phloem)

Epidermis forms the outer most layer of the plant cells. The epidermis in dry habitats is often

covered with a waxy layer called cuticle that prevents evaporation of water. This layer is

continuous without intercellular spaces and acts to protect the plant against physical damage

and pathogens. The epidermal layer on leaves and stems is interspersed with openings called

stomata, regulated by guard cells. This allows exchange of gases and transpiration. Epidermal

cells of roots have hair like projections that help to absorb water. As the plant grows, the

epidermis is replaced by the secondary meristem which is closely packed without intercellular

spaces. This begins to lignify creating a thick impervious layer. A chemical called suberin is

deposited that makes this impervious to water and gases.

(Refer video: Plant Tissues_Epidermal Cells)

3. Animal Tissues

Animal tissues can broadly be divided into four types – Epithelial, Muscular, Connective and

Nervous tissues.

a. Epithelial Tissue

This group of tissues form the outer covering and protective layer of animals. They form the

outer lining of all the organs and cavities in the body. Based on structure and functions, we can

divide epithelial tissues into four different types – Squamous epithelium, Cuboidal epithelium,

Columnar epithelium and Stratified squamous epithelium.

(Refer video: Animal Tissues_Types of tissues)

(i) Squamous Epithelium

They form an extremely thin and flat layer of tissues. They provide a very thin layer

important for gaseous exchange, thus providing permeability. They are present in

the lining of oesophagus and mouth.

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(ii) Cubiodal Epithelium

As the name suggests, they are cubiod in shape and form the lining of salivary glands

and kidney tubules. They provide mechanical support. They also form glandular

epithelium when they form glands.

(iii) Columnar Epithelium

These tissues line the organs which help in absorption and secretion , such as lining

of intestines. They are made up of elongated cells. When cilia is present on these

cells they form ciliated columnar epithelium like those present in the respiratory

tract.

Did you know?

Ciliated epithelium assists in removing dust particles

and foreign bodies which enter the air passages.

(iv) Stratified Squamous Epithelium

This kind of tissue is formed when multiple layers of squamous epithelium are

arranged in a pattern. Our skin is made up of this kind of tissue.

Question7. Identify A, B, C and D in the following figure.

A B

C D

(Refer video: Animal Tissues_Location of tissues)

b. Muscular Tissue

These tissues make up our muscules which are responsible for almost all the movements that

take place in the body. The muscles contain contractile proteins which bring about all the

contractions and relaxations in the muscles.

(Refer video: Animal Tissues_Muscular Tissue)

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Muscular tissues can be of three types – Striated muscle, Smooth muscle and Cardiac muscle. All the

voluntary movements carried out by our body is carried out by the striated or skeletal muscles. They

are called skeletal because these tissues are mostly attached to the bones. Further they are long,

cylindrical, unbranched with striations and are multinucleated.

Almost all the involuntary movements in the body are carried out by the smooth or unstriated muscles.

They are long, smooth, spindle shaped and uninucleate. We can find them in places like alimentary

canal and blood vessels.

Did you know?

Hardest muscle in the body is the chin

Question8. Why do you think smooth muscles are also called unstriated muscles?

Question9. Which is the strongest muscle in the body? How can you say it is the strongest?

(Refer video: Animal Tissues_Skeletal and Smooth Muscles)

Cardiac muscles make up our entire heart. These muscles are involuntary in nature and show rhythmic

contractions and relaxations. Structurally they may look quite similar to striated muscles but they are

branched, uninucleate and have intercalated discs.

(Refer video: Animal Tissues_Cardiac Muscles)

Question10. Identify A, B and C in the following figure.

A

B

C

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c. Connective Tissue

As the name suggests, these tissues help in connecting different parts of the body. For example,

blood is a connective tissue which transports oxygen, carbon dioxide, food, hormones and waste

materials from one part of the body to other. Blood is composed of a yellow coloured fluid

matrix called plasma and other cellular components like RBCs, WBCs and platelets are

suspended in it.

RBCs in blood impart it with the characteristic red colour. This red colour is due to the presence

of a iron containing pigment called haemoglobin.

(Refer video: Animal Tissues_Connective Tissues)

The various components of blood have very specific functions. The plasma helps in the

thermoregulation i.e. maintenance of constant temperature in the body. The RBCs play the vital

role of transporting oxygen to all parts of the body. WBCs form a major part of immune system

of the body and platelets help in clotting of blood in the case of an injury.

(Refer video: Animal Tissues_Types of Blood cells)

Question11. How do you think plasma regulates the body temperature?

Did you know?

A new born baby has just one cup of

blood in his/her body.

Bones form another set of connective tissue. They give the structural support to the body.They are non

flexible and are embedded in a hard matrix made up of calcium and phosphorus compounds. One bone

is connected to another bone with the help of ligaments which form strong elastic connective tissues

with very little matrix. Tendons are another type of connective tissues which connect muscles to bones.

They are very strong fibrous tissues with limited flexibility.

One more example of connective tissues is cartilage. These tissues are present in nose, ear, trachea and

larynx. They have widely spaced cells and have a matrix made up of proteins and sugars.

(Refer video: Animal Tissues_Bones, Ligaments and Tendons)

Areolar tissues are present in bone marrow, around blood vessels and between skin and muscles. They

help in repair of damaged tissues. The fats in the body are stored in adipose tissues in the form of fat

globules.Question12. Write one function each of aerolar tissue and adipose tissue.

(Refer video: Animal Tissues_Areolar and Adipose Tissues)

e.d. Nervous Tissue

This tissue is specialized to carry electrical signals throughout the body required to transmit information

and instructions. The nervous system is made up of brain, the spinal cord and several other nerves. The

brain is made up of nervous tissue and is essential for all sensations, consciousness, memory and

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emotion. The dendrites of a nerve cell pick up electrical signals and then transmit them to other cells

via the axon endings.

Question13. Label the parts in the following figure.

Question14. What are glial cells? What is their function?

(Refer video: Animal Tissues_Nervous Tissue)

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IX – Std. Tissues – Home work

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1. What is the shape of the epithelial tissue

A. Flat

B. Cuboidal

C. Columnar

D. All of the above

2. Sclerenchyma tissue is thickened due to presence of:

A. Suberin

B. Lignin

C. Chitin

D. Cutin

3. The covering tissue of external and internal surfaces of animals is:

A. Epithelial

B. Nervous

C. Connective

D. Muscle

4. Short branched process coming out of a soma of neuron are:

A. Dendrites

B. Axons

C. Neutrophils

D. Lymphocytes

5. Cardiac muscles are:

A. Branched

B. Striated

C. Involuntary

D. All of the above

6. Name the following.

i. The tissue that helps to transport food and oxygen in humans.

ii. The tissue that helps to store fat.

iii. The tissue that helps in movement.

iv. The tissue that helps in transport of water in plants.

7. State whether true or false.

i. The cornea of the eye is an example of stratified epithelium.

ii. Unstriated muscles are voluntary muscles.

iii. Sieve cells are the parent of xylem tissue.

iv. Epidermis tissue is a type of permanent tissue.

8. Match the following:

i. Blood and lymph a. epithelial tissue

ii. Bone and cartilage b. areolar connective tissue

iii. Tendon and ligament c. skeletal connective tissue

iv. Ciliated and Cuboidal d. fluid connective tissue

9. Why is meristematic tissue important for the plant?

10. Which tissue produces the red blood cells in humans?

11. Define:

i. Meristematic tissue

ii. Permanent tissue

iii. Connective tissue

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IX – Std. Tissues – Home work

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12. Name and explain different types of simple permanent tissues found in plants.

13. Give three features of cardiac tissue.

14. Make a flow chart to show different kinds of tissues found in animals.

15. Make a flow chart to show different kinds of tissues found in plants.

16. What will happen if:

i. Ligament is over stretched.

ii. Apical meristem is removed or damaged.

17. What are complex tissues? Name the complex tissues and their components found in plants.

18. Differentiate between:

i. Simple and complex tissue.

ii. Xylem and phloem

19. What are connective tissues? Explain different type of connective tissues with the help of diagram.

20. Make a list of all the tissues you can think of in human body and try to classify each of them. You

can also take the help of internet

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