MOTIONMOTION

RESTREST When a body does not change its position When a body does not change its position

with respect to time and its surroundings, with respect to time and its surroundings, the body is said to be at rest.the body is said to be at rest.

MOTIONMOTION When the position of a body continuously When the position of a body continuously

changes with respect to time and its changes with respect to time and its surroundings, the body is said to be in surroundings, the body is said to be in motion.motion.

RELATIVE MOTIONRELATIVE MOTION Motion is relative and not absolute:Motion is relative and not absolute: When When

you sit in a train, your distances from the wall, you sit in a train, your distances from the wall, ceiling and the floor of the compartment ceiling and the floor of the compartment remains constant. Your position is not changing remains constant. Your position is not changing as measured from the compartment but your as measured from the compartment but your distance from the platform is changing as time distance from the platform is changing as time passes. So you are moving with respect to the passes. So you are moving with respect to the platform but you are at rest with respect to the platform but you are at rest with respect to the compartment.compartment.

So, motion is not absolute. It depends on So, motion is not absolute. It depends on the body with respect to which all distances are the body with respect to which all distances are measured.measured.

THE EARTH IS MOVING THE EARTH IS MOVING

CHARACTERISTICS OF A CHARACTERISTICS OF A MOVING BODYMOVING BODY

1)1) There must be a reference point There must be a reference point (stationary object) to describe the (stationary object) to describe the position of the given body.position of the given body.

2)2) The position of the given body must The position of the given body must continuously change with time and with continuously change with time and with respect to the reference point.respect to the reference point.

DISTANCE DISTANCE Distance is the actual length of the path Distance is the actual length of the path

covered by a moving body irrespective of covered by a moving body irrespective of the direction in which the body moves.the direction in which the body moves.

Distance is a Distance is a scalarscalar quantity. It is quantity. It is expressed by the magnitude only. It has expressed by the magnitude only. It has no direction.no direction.

In SI system , the unit of distance is In SI system , the unit of distance is metremetre. . However we may use a bigger unit called However we may use a bigger unit called kilometre.kilometre.

DISPLACEMENTDISPLACEMENT Displacement is the shortest distance of a Displacement is the shortest distance of a

moving body from the point of reference moving body from the point of reference ( initial position of body), in a specified ( initial position of body), in a specified direction.direction.

It is a It is a vectorvector quantity. It is expressed by quantity. It is expressed by magnitude and direction.magnitude and direction.

In SI system, the unit of displacement is In SI system, the unit of displacement is metre metre and the bigger unit is kilometre.and the bigger unit is kilometre.

A B

Displacement

E

G

F

i) A-E-B = 20 kms

ii) A-F-B = 10 kms

iii) A-G-B = 25 kms

Out of 3 cases which one is the displacement of the object from A to B ?

Here the distance covered is 29 kms and the displacement is 0

DIFFERENCES BETWEEN DIFFERENCES BETWEEN DISTANCE AND DISPLACEMENTDISTANCE AND DISPLACEMENT

DISTANCEDISTANCE DISPLACEMENTDISPLACEMENT

1)1) It is the actual length of It is the actual length of the path travelled by a the path travelled by a moving object.moving object.

2) The direction need not 2) The direction need not be specified.be specified.

1)1) It is the shortest It is the shortest distance between the distance between the initial position ( point of initial position ( point of origin) and the final origin) and the final position of the objectposition of the object

2)2) The direction has to be The direction has to be specified with respect to specified with respect to the reference line.the reference line.

3) The distance 3) The distance covered in different covered in different directions can be directions can be added by simple added by simple arithmetic.arithmetic.

4) The distance 4) The distance covered by a moving covered by a moving object cannot be object cannot be zero.zero.

5) The distance is a 5) The distance is a scalar quantity.scalar quantity.

3) The displacements 3) The displacements in different directions in different directions cannot be added by cannot be added by simple arithmetic.simple arithmetic.

4) The displacements 4) The displacements of a moving object of a moving object can be zero.can be zero.

5) The displacement 5) The displacement is a vector quantity.is a vector quantity.

UNIFORM MOTIONUNIFORM MOTION When a body covers equal distances in When a body covers equal distances in

equal intervals of time, however small may equal intervals of time, however small may be time intervals, the body is said to be time intervals, the body is said to describe a uniform motion.describe a uniform motion.

Examples –Examples – An aeroplane flying at a speed of 800km/hAn aeroplane flying at a speed of 800km/h Light energy traveling at a speed of Light energy traveling at a speed of

3 x 103 x 1088 m/s m/s

NON- UNIFORM MOTIONNON- UNIFORM MOTION

When a body covers unequal distances in When a body covers unequal distances in equal intervals of time, it is said to be equal intervals of time, it is said to be moving with a non-uniform motion.moving with a non-uniform motion.

Examples –Examples – An aeroplane running on a runway before An aeroplane running on a runway before

taking off.taking off. A freely falling stone under the action of A freely falling stone under the action of

gravity.gravity.

SPEEDSPEED The rate of change of motion is called the The rate of change of motion is called the

speed speed oror Speed of a body is the distance travelled Speed of a body is the distance travelled

by it in a unit timeby it in a unit time The unit of speed in SI system is The unit of speed in SI system is metremetre

per secondper second (m/s) (m/s) For measuring larger speeds, the unit is For measuring larger speeds, the unit is

km/hkm/h..

QUESTIONSQUESTIONS

1)1) What is rest ?What is rest ?2)2) What is motion ?What is motion ?3)3) What is difference between distance and What is difference between distance and

displacement ?displacement ?4)4) What is speed ?What is speed ?5)5) What is uniform motion ? Give an What is uniform motion ? Give an

example.example.6)6) What is non-uniform motion ? Give What is non-uniform motion ? Give

example.example.

7) With the help of an example clearly explain 7) With the help of an example clearly explain distance and displacement.distance and displacement.

8) Supply a situation where displacement is 8) Supply a situation where displacement is zero but distance is not zero and both zero but distance is not zero and both distance and displacement is same.distance and displacement is same.

9) Why is motion not absolute ? Explain.9) Why is motion not absolute ? Explain.

10) Write the characteristics of a moving 10) Write the characteristics of a moving body ?body ?

11) The unit of speed is ------------.11) The unit of speed is ------------.

12) Displacement is a --------- quantity.12) Displacement is a --------- quantity.

13) The unit of distance used to measure the 13) The unit of distance used to measure the thickness of a book is --------.thickness of a book is --------.

14) The motion of the earth around the sun 14) The motion of the earth around the sun is ---------- ( uniform, non-uniform)is ---------- ( uniform, non-uniform)

15) When a stone falls from a height its 15) When a stone falls from a height its motion is ----------------.motion is ----------------.

AVERAGE SPEEDAVERAGE SPEED The average distance covered by a The average distance covered by a

moving body per unit timemoving body per unit time, Or , Or It is the quotient of total distance travelled It is the quotient of total distance travelled

by a body divided by the total time taken to by a body divided by the total time taken to cover the distance.cover the distance.

Total distance traveled Total distance traveled Average speed = --------------------------------Average speed = --------------------------------

Total time takenTotal time taken

v =(sv =(s11+s+s22+s+s33 ….)/ (t ….)/ (t11 + t + t22 + t + t33….)….)

ProblemsProblems 1) A train starts from rest and covers a distance of 450 1) A train starts from rest and covers a distance of 450

m in 2 min. Calculate the speed of the train in i) m/s ii) m in 2 min. Calculate the speed of the train in i) m/s ii) km/hkm/h

2) A train travels a distance of 2o km with a uniform 2) A train travels a distance of 2o km with a uniform speed of 60 km/h. It travels another distance of 40 km speed of 60 km/h. It travels another distance of 40 km with a uniform speed of 80 km/h. Calculate the with a uniform speed of 80 km/h. Calculate the average speed of the train.average speed of the train.

3) A boy runs first 100m with a uniform speed of 8 m/s 3) A boy runs first 100m with a uniform speed of 8 m/s and the next 200m with a uniform speed of 5 m/s. and the next 200m with a uniform speed of 5 m/s. Calculate the average speed of the boy.Calculate the average speed of the boy.

VELOCITYVELOCITY The distance covered by a body per unit The distance covered by a body per unit

time in a specified direction is called the time in a specified direction is called the velocity. velocity. Or Or

The speed of a body in a specified The speed of a body in a specified direction is called the velocity. direction is called the velocity. OrOr

The rate of change of displacement is The rate of change of displacement is called the velocity.called the velocity.

The SI unit of velocity is The SI unit of velocity is m/sm/s and the larger and the larger unit is km/hunit is km/h

UNIFORM VELOCITYUNIFORM VELOCITY When a body covers equal distances in When a body covers equal distances in

equal intervals of time ( however small equal intervals of time ( however small the time intervals may be ) in a the time intervals may be ) in a specified direction, the body is said to specified direction, the body is said to be moving with a uniform velocity.be moving with a uniform velocity.

Examples – Examples – A train running towards south with a A train running towards south with a

speed of 50 km/hspeed of 50 km/h An aeroplane flying north with a speed An aeroplane flying north with a speed

of 300 km/hof 300 km/h

NON- UNIFORM VELOCITYNON- UNIFORM VELOCITY

When a body covers unequal When a body covers unequal distances in equal intervals of time distances in equal intervals of time in a specified direction or when a in a specified direction or when a body covers equal distances in body covers equal distances in equal intervals of time, but its equal intervals of time, but its direction changes, then the body is direction changes, then the body is said to be moving with variable said to be moving with variable velocity.velocity.

CONDITIONS FOR VARIABLE CONDITIONS FOR VARIABLE VELOCITYVELOCITY

Either of the following conditions should Either of the following conditions should be satisfied by a moving body, with a be satisfied by a moving body, with a variable velocity.variable velocity.

i) It should cover unequal distances in i) It should cover unequal distances in equal intervals of time in a specified equal intervals of time in a specified direction.direction.

ii) It should cover equal distances in equal ii) It should cover equal distances in equal intervals of time, but its direction must intervals of time, but its direction must change.change.

EXAMPLE OF VARIABLE EXAMPLE OF VARIABLE VELOCITYVELOCITY

A car running towards north on a busy road has A car running towards north on a busy road has a variable velocity, as distances covered by it a variable velocity, as distances covered by it per unit time changes with change in the road per unit time changes with change in the road conditions.(change in distance)conditions.(change in distance)

The blades of a rotating ceiling fan, a person The blades of a rotating ceiling fan, a person running around a circular track with constant running around a circular track with constant speed, etc., are the examples of variable speed, etc., are the examples of variable velocity, as the direction of the moving body velocity, as the direction of the moving body changes in each case.( change in direction)changes in each case.( change in direction)

AVERAGE VELOCITYAVERAGE VELOCITY

Average velocity is the arithmetic mean of initial Average velocity is the arithmetic mean of initial velocity ( starting velocity) and the final velocity for a velocity ( starting velocity) and the final velocity for a given period of time.given period of time.

If u is the initial velocity and v is the final velocity after If u is the initial velocity and v is the final velocity after time interval t, the average velocity time interval t, the average velocity

v v avav = (u+v)/2 = (u+v)/2

Average velocity = (Initial velocity + final velocity)/2Average velocity = (Initial velocity + final velocity)/2

DIFFERENCES BETWEEN DIFFERENCES BETWEEN SPEED AND VELOCITYSPEED AND VELOCITY

SPEEDSPEED VELOCITYVELOCITY

1.1. The distance covered The distance covered per unit time is called per unit time is called speed.speed.

2.2. It is a scalar quantity.It is a scalar quantity.

1.1. The distance covered The distance covered per unit time in a per unit time in a specified direction is specified direction is called velocity.called velocity.

2.2. It is a vector quantity.It is a vector quantity.

ACCELERATIONACCELERATION The rate of change of velocity of a moving body The rate of change of velocity of a moving body

is called acceleration. Oris called acceleration. Or The change of velocity of a moving body with The change of velocity of a moving body with

respect to time is called acceleration.respect to time is called acceleration. The rate of change of velocity, when the The rate of change of velocity, when the

velocity increases is called positive velocity increases is called positive acceleration.acceleration.

The rate of change of velocity, when the The rate of change of velocity, when the velocity decreases is called negative velocity decreases is called negative acceleration or decceleration.acceleration or decceleration.

change in velocitychange in velocity Acceleration = -------------------------Acceleration = -------------------------

TimeTime The unit of acceleration = m/sThe unit of acceleration = m/s22 or ms or ms-2-2

Acceleration is a vector quantity, as it is Acceleration is a vector quantity, as it is expressed in magnitude and direction.expressed in magnitude and direction.

UNIFORM ACCELERATIONUNIFORM ACCELERATION

When a body undergoes equal changes in When a body undergoes equal changes in velocity in equal intervals of time ( however velocity in equal intervals of time ( however small the time interval may be), the body is said small the time interval may be), the body is said to be moving with a uniform acceleration.to be moving with a uniform acceleration.

Examples – A freely falling body under the pull Examples – A freely falling body under the pull of the Earth has a uniform acceleration.of the Earth has a uniform acceleration.

A marble rolling down an inclined plane has a A marble rolling down an inclined plane has a uniform acceleration.uniform acceleration.

NON-UNIFORM ACCELERATIONNON-UNIFORM ACCELERATION

When a body describes unequal When a body describes unequal changes in equal intervals of time, changes in equal intervals of time, the body is said to be moving with the body is said to be moving with non-uniform acceleration.non-uniform acceleration.

For Example – A car moving on a For Example – A car moving on a busy roadbusy road has a non-uniform has a non-uniform acceleration.acceleration.