PHYSICS MR. BALDWINREVIEW 10/4/13

Aim: What have we done so far? Let’s review.

Do Now: Please take out your notebooks and make a list of what we have done so far?

HOMEWORK:

Prepare for TEST on Monday 10/7/13.

A brief review sheet will be posted online.

1. Rules of Significant figures.

2. Scientific and decimal notation

3. 7 basic Units of measurement

4. Precision & Accuracy

5. Order of magnitude

6. Unit conversions between metric and BEU; between metric

7. Scalars and vectors– Definition & Components of vectors

– Examples of both: Speed, distance, and time are scalar quantities; Velocity, displacement and acceleration are all vectors.

8. Making line graphs

9. Constant and accelerated motion.

10. Freefall Motion

11. Distance & velocity-time graphs.

7 Basic Units of Measurement

In Physics, we will be working in the SI system, where the basic units are kilograms, meters, and seconds (m.k.s).

METRIC PREFIXES revised

These are the standard SI prefixes for indicating powers of 10.

CHECK

Can you give any common everyday examples where these prefixes are used?

Section Check

A car is moving at a speed of 90 km/h. What is the speed of the car in m/s? (Hint: Use Dimensional Analysis)

Question

A. 2.5×101 m/s

B. 1.5×103 m/s

C. 2.5 m/s

D. 1.5×102 m/s

90 km

hr

1000

1

m

km

1hr

60 min

1min

25 /

60m s

s

Order of Magnitude: Rapid Estimating

A quick way to estimate a calculated quantity is to round off all numbers to one significant figure and then calculate. Your result should at least be the right order of magnitude; this can be expressed by rounding it off to the nearest power of 10.

Section Check

Calculate approximately how many basketballs (diameter = 75cm) can fit in this classroom randomly AND orderly stacked one atop the other?

• Accuracy: • How close you are to the

actual value

• Depends on the person measuring

• Calculated by the formula:

% Error = (YV – AV) x 100 ÷ AV

Where: YV is YOUR measured Value & AV is the Accepted Value

• Precision: • How finely tuned your

measurements are or how close they can be to each other

• Depends on the measuring tool

• Determined by the number of significant digits

Accuracy & Precision

Components of Vectors

If the components are perpendicular, they can be found using trigonometric functions.

Addition of Vectors: ResultantFor vectors in same or

opposite direction, simple addition or subtraction are all that is needed.

You do need to be careful about the signs, as the figure indicates.

Recall• Graphs are made using pairs of numbers (x,y). • independent variables are plotted on the x-axis. • dependent variables are plotted on the y-axis.• Range is the difference between smallest and

largest value for a variable• Scale determined by dividing the range by the

number of data points and rounding off to the nearest integer.

• Titles must be give to graph &placed on both axes

12

• Uniform motion refers to motion that has a constant velocity– Speed & direction remains the same– Such as your car on cruise control– Moving at 50 mph on a straight road

• Accelerated motion refers to motion with changing velocity– As you round a curb– Hit the gas or brake

Uniform & Accelerated Motion

13

Average Speed & Instantaneous Speed• The instantaneous speed is the speed as given on your speedometer. The speed at that instant.

•Speed given by the speedometer

dv

t

• The average speed is the total distance traveled by an object divided by the total time taken to travel that distance.

CHECK: Determine the units

Unit: m/s; km/h; mph

14

CHECKCHECK: : Can you write other forms Can you write other forms of the equation to determine the other of the equation to determine the other

two quantities two quantities tt & & dd??

dt =

d

=t

d v t

15

AccelerationAcceleration is the change of velocity divided by time.

f iv va

t

Unit: m/s2Determine its Unit.

Where a: acceleration; vf: final velocity; vi:initial velocity

16

Equations of Motion

2

2 2 2 2

For Uniform (Constant) Motion, we use

; OR

For Accelerated Motion, we use

OR

1

2

2 OR 2

f if i

i

f i f i

d dv t d v t

t v

v vv v at a

t

d v t at

v v ad v v ad

17

Uniformly Accelerated Motion

Galileo’s Law of Freely Falling Bodies:

In the absence of air resistance, all objects, regardless of size, shape or mass, fall with the same acceleration.

180

5

10

15

20

25

0 1 2 3 4 5

Finding Speed: What can you say about the slope of the graph at any time?

The slope of the tangent to the distance-time graph at any point is the instantaneous speed at that point.

4.00 m/s

8.00 m/s

19

0.00

2.00

4.00

6.00

8.00

10.00

0.00 1.00 2.00 3.00 4.00 5.00

TIME (s)

SP

EE

D (

m/s

)Speed-Time Graph of Uniformly Accelerated Motion

f iv v at Slope gives acceleration of the body at each point.

4.00 m/s

2.00 s

Slope 2.00 m/s2

20

Graphical Analysis of Linear Motion

The area beneath the velocity-time graph gives you the Distance travelled

CHECKHow would you find the area under the velocity-time graph?

TEST YOURSELF…WHAT DO YOU UNDERSTAND? SCIENTIFIC & DECIMAL NOTATION

How do you write a decimal in scientific notation?What is the form?

 METRIC PREFIXES

What are the metric prefixes?What values do the symbols represent?

 MOTION

What is motion?How do you measure motion?

 SCALARS & VECTORS

What is a Scalar?What is a Vector?Give some examples of both scalar and vector quantities.

 VELOCITY

What is Velocity?What is the formula for Velocity?What is the Unit?Is it a Scalar or Vector?

 ACCELERATION

What is Acceleration?What is the formula for acceleration?What is the unit for acceleration?

PHYSICS MR. BALDWINNEWTON’S LAWS 10/8/13

Aim: Would a hockey puck sliding on a frictionless ice ever stop?

Do Now: What forces are acting on you as you sit in your seat?

Homework: “Motion is the rule, not the exception.” Think about this statement. Find some interesting quotes on your own by Isaac Newton.

Newton’s First Law

The Law of Inertia

Laws of Motion: Questions for ThoughtLaws of Motion: Questions for Thought

• What makes something originally at rest begin to move?

• Why do some things move faster than others?

• Why are some objects accelerated and others not?

Question: What Causes an Acceleration?

• If a body changes in its state of rest or uniform motion, then it underwent an acceleration.

• What caused this?– A force– Simply described as a push or pull on and object.

• Thus, a net unbalanced force changes the object’s state of inertia– i.e. state of rest or uniform (constant) motion

• A net unbalanced force causes an acceleration• NOTE: A force is not a characteristic of an object. “It

is something that one object does to another.”

Contact Forces Action-at-a-Distance Forces

Frictional Force Gravitational Force

Tension Force Electrical Force

Normal Force Magnetic Force

Air Resistance Force

Applied Force

Spring Force

CHECK: What are some examples of force?

Newton’s First Law of MotionNewton’s First Law of Motion

• Constant velocity is as natural as being at rest.

• If you give a ball a push on a frictionless floor, it would move forever.

• This conclusion was first reached by Galileo and later stated by Newton as his first law of motion.

Newton’s First Law of Motion

Newton’s first law is often called the law of inertia.

Every object continues in its state of rest, or of uniform motion in a straight line, unless acted upon by an unbalanced (external) force.

Examples of InertiaExamples of Inertia

Newton’s First Law of Motion states:Newton’s First Law of Motion states: If no net unbalanced force acts on it, an object at rest remains at rest and an object in motion remains in motion at a constant velocity (that is at constant speed in a straight line).

END. Test your skills

• http://phet.colorado.edu/sims/lunar-lander/lunar-lander_en.html

PHYSICS MR. BALDWINNEWTON’S 2nd LAW 10/15/13

Aim: Why are some objects accelerated faster then others?

Do Now: Is it ever possible for a steel rod and a handful of feathers to have the same mass? Explain.

Homework: Worksheet : Newton’s 2nd Law

Do Problems 6 - 10

What is Inertia?What is Inertia?

Inertia is the tendency of an object to resist any change in its state of rest or uniform motion.

The mass of a body is the property of matter that manifests itself as inertia. In other words, mass is a measure of

inertia.

What is Mass?What is Mass?

MassMass

• Mass may be thought of as a quantity of matter contained in an object.– Matter is anything that occupies space

• The greater an object's mass, the greater the object's inertia.

• The SI unit for mass is the kilogram (kg).

Force Force CHECKCHECK..• According to the first law, can an object

begins to move all by itself?

• No! A force is needed to start it moving.

• If an object is moving in a straight line, will it continue to move in a straight line at a constant velocity?

• Yes! Unless a force acts to slow it down, speed it up, or changes its direction.

Therefore, what can you conclude Therefore, what can you conclude about a force?about a force?

• A force is any influence that can change the speed or direction of motion of an object.

• A force is any influence that can cause an object to be accelerated.

What variables determine whether an object accelerates?

• If you push the same chair with two different

forces (one small & one large), describe its

motion?

• What can you conclude about your choice?

• If you push a chair and a table with the same

force, which one accelerates faster?

• What can account for your choice?

Newton’s Second Law of Motion

Newton’s second law is the relation between acceleration and force. It states, the acceleration of an object is proportional to force and inversely proportional to its mass.

Force is a vector

• Force is a vector, so .

• NOTE: The direction of the

acceleration is always in the same

direction as the force.

amFnet

The Newton: The Unit of Force

The unit of force in the SI system is the Newton.

Unit: 1 N = 1 kg·m/s2

Note that the pound is a unit of force, not of mass.

Now, Derive the base units of force from the equation.

The Newton: the unit of forceThe Newton: the unit of force

• The SI unit of force is the Newton (N)

• 1 Newton = 1 N = 1 (kg)(m/s2)

• The pound (lb) is the unit of force in the British system of measurement

• 1 lb = 4.45 N (1 N = 0.225 lb)

F ma

A force of 1 Newton gives a mass of 1 kilogram an acceleration of 1 m/s2

Force

The magnitude of a force can be measured using a spring scale.

Worksheet: DO problems 1 – 5

• Acarispulledwithaforceof10,000N.Thecar'smassis1267kg.But,thecarcovers394.6 min15seconds. (a) Whatisexpectedaccelerationofthecarfromthe10,000Nforce? (b) Whatistheactualaccelerationofthecarfromtheobserveddataofxandt? (c) Whatisthedifferenceinaccelerations? (d) Whatforcecausedthisdifferenceinacceleration? (e) Whatisthemagnitudeanddirectionoftheforcethatcausedthedifferencein acceleration?

DEFINITIONS

• Collinear Forces: forces whose vectors lie along the same straight line.

• Concurrent Forces: Forces whose line of action pass through a common point.

F1

F2

F3

F1

F2

F3

PHYSICS MR. BALDWINNEWTON’S 3rd LAW 10/17/13

Aim: What is the difference between mass and weight?

Do Now: QUIZ (8 min)

Take out your Newton’s 2nd law worksheet and do #11 on a sheet of paper & turn in.

Homework:

Effect of Force on MassEffect of Force on Mass: Complete the following statement

• When forces of different magnitudes act upon different objects of identical masses, the greater force produces the greater/lesser acceleration.

• When the same force acts on objects of different masses, the greater mass receives the greater/smaller acceleration.

Friction: just another forceFriction: just another force• Friction is a force that acts to oppose the

motion of an object with which it is in contact.– The harder the objects are pressed

together, the stronger the frictional force.

– Friction is an actual force, unlike inertia.

??? Question for Thought ???

• An astronaut has a mass of 80 kg on earth. What will his mass be on the Moon? Calculate or Explain.

• Describe what would happen to the spring in a bathroom scale if you were on the moon when you stepped on it. How is this different from stepping on the scale on Earth?

• http://phet.colorado.edu/sims/mass-spring-lab/mass-spring-lab_en.html

Weight – the Force of Gravity

Weight is the force exerted on an object

by gravity. Close to the surface of the

Earth, where the gravitational force is

nearly constant, the weight is:

w mg

The Newton: the unit of forceThe Newton: the unit of force

• Weight is a Force. SI unit of weight is the Newton (N)

• The pound (lb) is the unit of force in the British system of measurement

• 1 lb ≈ 4.45 N OR (1 N = 0.225 lb)

• Mass/Weight equivalence:1 kg ≈ 2.2 lbs.

CHECK.What is your mass in Kilograms?

kglbs

kglbs 82

2.2

1180

CHECK.What is your weight in Newtons?

2

2

Mass, 80.0

Weight,

80.0 9.80 /

780 / 780

m kg

w mg

w kg m s

kg m s N

Convert your weight from Pounds to Newtons?

Weight, 180

1 4.45

4.45Therefore, 180 180 800

1

w lbs

lbs N

Nlbs lbs N

lb

What is the weight, in Newtons, of a 1200 kg automobile?

2

2

Mass, 1200

Weight,

1200 9.80 /

11760 / 11.76

m kg

w mg

w kg m s

kg m s kN

Weightlessness

• Are you ever weightless?

– w = 0

• Weightlessness is just a sensation

• Have you ever experienced weightlessness?

PHYSICS MR. BALDWINNEWTON’S 3rd LAW 10/18/13Aim: What is Newton’s 3rd law?

Do Now: REAL QUIZ (8 min)

A rocket accelerates in a space at a rate of 1-g. The rocket exerts a force of 2482 N. (i) What is the mass of the rocket? (ii) Later in flight, the rocket exerts a force of 46,458 N. What is the rocket’s new acceleration? What is the rocket’s new acceleration in g’s?

Homework:

Newton’s Third Law of Motion

Law of Force Pairs:

All forces occur in pairs

For every action force there is an equal and

opposite reaction force.”

Newton’s Third Law of Motion

Any time a force is exerted on an object, that force is caused by another object.

Newton’s third law: law of force pairs

Whenever one object exerts a force on a second object, the second exerts an equal force in the opposite direction on the first.

Newton’s Third Law of Motion

A key to the correct application of the third law is that the forces are exerted on different objects. Make sure you don’t use them as if they were acting on the same object.

Newton’s Third Law of MotionRocket propulsion can also be explained using Newton’s third law: hot gases from combustion spew out of the tail of the rocket at high speeds. The reaction force is what propels the rocket.

Note that the rocket does not need anything to “push” against.

WHAT ARE the reaction forces?

• Action: the tires on a car push on the road…

• Reaction: the road pushes on the tires.

• Action: while swimming, you push the water backwards...

• Reaction: the water pushes you forward.

• Action: a rocket pushes out exhaust…

• Reaction: the exhaust pushes the rocket forward

You come up with other examples of action-reaction forces?