# Conceptual Class Notes Semester 1

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29 Νοε 2013 (πριν από 4 χρόνια και 5 μήνες)

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1

2

What is Physics?

Four Forces

Scientific Method

Linear Motion

Speed and Velocity

Lab:
Finding Distance and Average Speed

Acceleration

Lab: Finding Acceleration and

Final Velocity

Freefall

Class Activity:

Measuring Reaction

Time

Class Activity:

How Fast and High can

you throw a ball?

Chapter 2 Review

Projectile Motion

Vectors and Components

Projectile Motion

Lab: Determining Projectile Velocity

Upwardly Launched Projectiles

Chapter 3 Review

3

Unit II

Laws of Motion

Newton’s 1
st

Law of Motion

Mass, Weight, and
Volume

Inertia

Equilibrium and Net
-
Force

Newton’s 2
nd

Law of Motion

Newton’s Second Law

Lab: Newton’s 2
nd

Law

Friction and Air Resistance

Pressure

Class Activity: Weighing a Car

Newton’s 3
rd

Law of Motion

Newton’s 3
rd

Law

Unit II Review

Momentum

Momentum and Impulse

Bouncing and Collisions

Law of Conservation of Momentum

Chapter 7 Review

4

Electrostatics

Electrical Forces and Charges

Methods of Charging

Coulomb’s Law

Electric Current

Flow of Charge

Ohm’s Law

Source of Electrons

Electric Power

Class Activity:

Electric Cooking with

Julia Childs

Electric Circuits

Series Circuits

Exploratory Activity: Series
Circuits

Parallel Circuits

Exploratory Activity: Parallel Circuits

Compound Circuits

Electricity Unit Review

Magnetism

Magnetic Fields

Electromagnetism

Transformers

5

Chapter 1 Highlights
:

The Four
Natural Forces

Scientific Method

Key Terms

Force

Matter

Motion

Energy

Scientific Method

Facts

Laws

Principles

Hypothesis

Theory

6

What is Physics?

The study of matter and energy, the motion of matter, and
forces on matter

Involves
the study of four things and their interactions

1.

Matter

all objects are composed of massive particles

2.

E
nergy

the release of energy produces force on matter or to another
form of energy

3.

F
orces

change the state of motion or energy

4.

M
otion

Newton’s
laws of motion that governs all material objects

The Four Natural Forces

1.

Gravity

force between matter (planets, falling objects)

Electromagnetic

force between charges (electricity, lightning)

Weak Nuclear

Strong Nuclear

force that holds the nucleus together (nuclear power)

Why is physics the basic science?

Physics is fundamental to all the other
sciences
. Physics explains the prop
erties and processes of Chemistry and
Biology.

What is the language of physics? Why? (4 main reasons)

Math. It: predicts,
provides proof, universal, logical

Scientific Method

1.

Identify the Problem

2.

Form a hypothesis

3.

Perform experiments

4.

Make Observations

5.

Form Conclusion

7

Facts

known pieces of information that are true for scientists

Laws/Principles

organized group of facts that have been tested and are shown
true over experimentation.

Hypothesis

educated guess on organizing data or before

Must be testable!

Theory

a hypothesis with some supporting evidence

By definition

can’t be proved

Is the scientific method followed strictly? Explain.

No. sometimes a step is
skipped due to the nature of the problem. New
information is found through
experimentation and the hypothesis is changed. Conclusions can be false and
the process starts over.

Underlying all scientific theory/models are assumptions

What are
assumptions
?

Are things that make models easier to use.

Example

atomic theory;

protons, neutrons, electrons are not small spheres?
They don’t “orbit” the way they are pictured (modeled).

When are theories, models, hypotheses changed?

When there is conclusive

Assignment Ch. 1: RQ 1
-
5

8

Chapter 4

Highlights:

Vector and Scalar Quantities

Average Speed vs. Instantaneous Speed

Speed vs. Velocity

How Velocity Changes

Constant Speed and Distance

Constant Acceleration and Distance

Freefall

Acceleration

Key Terms

Speed

Instantaneous Speed

Average Speed

Velocity

Vector

Scalar

Acceleration

Gravity

Freefall

Acceleration due to Gravity

9

Review of how we measure things in science:

SI Units

(Systeme’Internationale)

International
standard for the
measurement of scientific data

SI Unit

English (American) Unit

Length

Meter (m)

Foot (ft)

Time

Second (s)

Second (s)

Weight

Newton (N)

Pound (lb)

Mass

Kilogram (kg)

Slug (sl)

Velocity

m/s

ft/s

Acceleration

m/s
2

ft/s
2

How fast can you run?

How fast is telling us your speed.

Student example running down and back in the hallway. Collect data, calculate
average speed. Discuss results.

Speed =

Speed gun measurement =

What do you need in order to determine this?

1.

A measurement of
distance

2.

A measurement of
time

to cover the
distance
.

3.

A reference point = usually a stationary point.

Speed

(units =

m/s

)

is a rate at which distance is covered per unit
time.

Speed =

dist./time

SI Units =

m/s

American Units =

ft/s

10

The speed or motion of an object is

relative

to other measuring points.

What is meant by this statement?
With respect to a common measuring point.

What do we commonly take measurement relative too? Why?

The surface of the
earth. It is common to everyone.

If a car traveled an average 25 mph for 2 hours, what distance did it

travel?
Discuss.

25 mph x 2 hours =

50 miles?

Without a reference point the car could’ve traveled 0 miles to 50 miles.

Instantaneous Speed

(speedometer of a car)

how fast an object is traveling
at a moment in time.

Average Speed

total distance trave
led in a period of time. It ignores
changes in direction
.

Velocity

speed with direction.

-
distance traveled from a reference
point (displacement) per unit time.

Need direction

velocity is a vector

Scalar

just a descriptive number

25 kg, 30 N, 98.6
o
F

Vector

a scalar with a direction
Œ

50 m/s due north, 30 N to the right

1.

The speedometer in every car also has an odometer that records the
distance traveled.

a.

If the odometer reads zero at the beginning of a trip and 35 km

a
half hour later, what is the average speed?

Speed = 35 km

/ ½ h = 70 km/h

Would it be possible to attain this average speed and never exceed
the average speed from
a
?

No. By definition of average there must
be a point where you’re traveling faster than

11

2.

If a cheetah can maintain a constant speed of 25 m/s, it will cover 25
meters every second. At this rate, how far will it travel in 10 seconds?
In one minute?

S =

d /t ; d = s t

D= 25 m/s (10s) = 250 m ; 25 m/s (60 s) = 1500 m

3.

The speedom
eter of a car moving northward reads 60 km/h. It passes
another car that travels southward at 60 km/h. Do both cars have the
same speed? Do they have the same velocity?

Yes. No, they are traveling in different directions!

Assignment Ch.
4: 1
-
5, 26
-
31

12

Name(s):

_________________

_________________

Period:

___
______________

Purpose:

To find the average speed of a student by measuring distance and time. The
student will then use one of the calculated average speeds to predict an
unknown distance. The student may use any materials as necessary.

Procedure:

The s
tudent will measure five (5) different ways the student can travel the
distance (i.e., run, walk, hop, skip, leap, crawl, cart wheel, etc.). For
each race, try to keep your speed as constant as possible throughout the
distance traveled!

Be sure to
SHOW AL

Activity

Time (sec.)

Distance (m)

Ave. Speed (m/s)

1

2

3

4

5

Calculate your average speed in the space below:

Use ONE of your activities from above to calculate an unknown distance:

13

1.

2.

Were there instances, in the same activity, where you were traveling

3.

Were you traveling at a constant speed throughout the whole distance?
What was happening to your speed throughout the distance you traveled?

4.

What were some of the things you ignored during your timed trials?

5.

Convert each of your average spee
ds into miles per hour just for
comparison. (1 m/s = 2.24 mph)

14

If you are stopped at an intersection and y
ou want to travel the next 50
miles in 1 hour. What average speed must you have?

50 miles per hour.

Was there a point at which you were traveling faster than this average?

Yes. It is an average.

speed? Discuss.

Could be 0 mph. Top speed of your car.

changed throughout the trip. How do you know your velocity changed, and what
did the car do in order to change it?

You fel
t your body being pushed, pulled in different directions

accelerate.

Demo: student on rolling chair

1.

Step on gas

accelerate

pick up speed

Step on brake

decelerate

lose speed

Turn

changes direction

Acceleration

(units = _
m/s
2
______)
the rate of change in velocity per unit
time.

* Velocity is a vector which has direction!
Change in

is final velocity
minus initial velocity.

a

= __
V
______

a =
Velocity

t

time

Rearrange this equation gives us the instantaneous velocity when
undergoing a constant acceleration:

V

=
a t

If a car accelerates constantly from rest to 60 mph (27 m/s) in 6 seconds:

a.

What is the cars acceleration?

A = (27m/s

0 m/s) / 6 s = 4 ½ m/s
2

b.

What is the cars average speed?

S = (27 + 0) /2 = 13 ½ m/s

What distance did the car travel in this time period?

D = s t = 13 ½ m/s (6 s) = 81 m

15

Fill in the following table of an object
accelerating at 5 m/s
2

with the time
values given:

Time (s)

Instantaneous Velocity (m/s)

Distance Traveled (m)

0

0

0

1

5 m/s

2 ½

2

10 m/s

10

3

22.5 m

4

40 m

5

62 ½

Calculations:

Under constant acceleration, as the time increases the velocity increases the
same amount each
second. What happens to the distance covered each second
under constant acceleration?

It increases also. Every second the speed
increases; the distance covered each 1 second time interval also gets larger.

Equation that describes the distance covered from

rest while constantly
accelerating:

d

½ a t
2

16

1.

Suppose a car moving in a straight

each second, first from 35 to 40 km/h, then from 40 to 45 km/h, then
from 45 to 50 km/h. What is its acceleration?

5 km/h/s

2.

In 5 seconds a car moving in a straight line increa
ses its speed from
50 km/h to 5
5 km/h, whi
le a truck goes from rest to 15 km/h. Which
undergoes greater acceleration? What is the acceleration of each
vehicle?

Truck. 1 km/h/s, 3 km/h/s

3.

During the span of 1 second, an object starts at 10 m/s and ends at 20
m/s. What is the average speed of th
e object during this time interval?
What is its acceleration?

S = (20 + 10)/ 2 = 15 m/s

A = (20

10)/ 1 s = 10 m/s
2

Assignment Ch.
4: 6
-
9, 32
-
36

17

Name(s):

_________________

_________________

Period:

_________________

Purpose:

To calculate the acceleration and final velocity of a match
-
box car

rolled
down a ramp at increasing angles.

Procedure:

Measure the distance the matchbox car will travel down the ramp and measure
the time taken to cover that distance. Note how the velocity of the matchbox
changes as it rolls down the ramp. Also note how

the accelerations of the
matchbox car are different for increasing angles.

Angle (Deg.)

Acceleration (m/s
2
)

Velocity (m/s)

10

30

50

70

90

18

1.

How do you know your matchbox car accelerated?

2.

What happened to the value of the matchbox cars

acceleration as the ramp
angle was increased?

3.

What happened to the matchbox cars final velocity as the ramp angle was
increased?

4.

What were some of the things that were difficult to measure in this lab?

5.

What happened when the matchbox car was
on the incline at 90
o
?

6.

What do you think would be the maximum acceleration of a matchbox car in
this kind of experiment? When does this occur?

19

When a skydiver jumps out of an airplane at 14,000 ft, she is said to be in
freefall. Wh
at is freefall? What happens when freefall occurs?

Gravity is pulling the skydiver down. The skydiver accelerates downward
toward the earth.

Video:

Skydiving

Demos:

book vs. paper

paper ball vs. book

penny and paper in a vacuum

In freefall, what qua
ntity do we ignore, or limit?

Air resistance. It slows things down.

How does a freely falling object drop?

Downward

toward the center of the earth.

Does it pick up speed as it falls from rest? How do we know? Does it have a
value or number?

Yes. It
started from rest and now it is traveling at a certain speed. Yes, it
is considered constant when near the surface of the earth.

How can we figure it out? Discuss.

Yes. Use a motion equation.

Freefall

an object accelerating downward by gravity wi
thout air resistance.

20

Name(s):

_________________

_________________

Period:

_________________

Purpose:

Calculate the acceleration due to gravity by dropping a softball from a large
known height and measuring the time taken to fall that distance.

Distance = 5.7 m

Measure the time with a stop watch:

Use your distance equation to calculate the value of the acceleration.

Calculated acceleration = ________________

Time (s)

Average time = _________

21

The accepted value for the ac
celeration due to gravity
: g =
9.806 m/s
2

For practical purposes: g = 10 m/s
2

That means for every second of fall, or for every second an object is
falling, the object will gain __
10
___ m/s downward.

What h
appens when a ball is thrown upward?

It travels upward
,

then stops instantaneously, and comes back down.

What happens to the balls velocity as it travels upward? Why does it do this?

It slows down until it reaches the top.
The acceleration due to gravity

is
opposite to the velocity of the ball.

What is the rate of this change?

It slows down at 10 m/s every second until it reaches the very top.

What happens to the balls velocity on the way down?

It speeds up on the way down.

What is the rate of this
change?

The rate is that of gravity = 10 m/s every second.

1.

What would be the speedomet
er reading on a falling rock after 1 second
of fall? 2 seconds? 4 seconds? 8 seconds?

V = g

t ; v = 10 (1 s) = 10 m/s,

20 m/s, 40 m/s, 80 m/s

2.

What would be the odometer reading on a falling rock after 1 second of
fall? 2 seconds? 4 seconds? 8 seconds?

D
= ½ g t
2

= ½ 10 t
2

= 5 t
2

= 5 (1)
2

= 5 m,

20 m, 80 m, 320 m

22

3.

A ball is thrown upward with a speed of 30 m/s. Calculate the speed of
the ball 1 second after the throw. 2 seconds. 3 seconds. 4 seconds. 5
seconds. 6 seconds.

20 m/s, 10 m/s, 0 m/s,
-
10 m/s,
-
20 m/s,
-
30 m/s

a.

What do you see happening to the velocity of the ball?

Slowing down at 10 m/s on the way up, then speeding up downward.

b.

Explain what happens to the ball after 3 seconds.

The ball is instantaneously stopped at the very top

it is the
turn
-
around
point.

c.

Explain what is happening to the ball at 6 seconds.

At the
6

second mark it is at the same level that it was thrown

and traveling
with the same speed but opposite direction
.

Assignment Ch.
4:
10
-
15, 18, 19, 37
-
41

23

Can you grab this package of M&Ms before it strikes the ground given these
initial conditions?

No. the time it takes for you to clasp your fingers is
more than

the time required for gravity to accelerate it from between your
fingers.

Name(s):

_________________

_________________

Period:

_________________

Purpose:

Measure your reaction time by using the distance equation.

Procedure:

Have your lab partner drop a meter stick or ruler between your index finger
and thumb.

ruler. The lab partner then drops the ruler and you grab it as fast as you
can. The time it takes gravity to pull the ruler down a distance equal to the
where your fingers grab the ruler is your

reaction time.

Use your distance equation to calculate the value of the reaction time. SHOW

Distance (m)

Time (s)

Average time =

24

Name(s):

_________________

_________________

Period:

_______
__________

Purpose:

Calculate how fast a person can throw a ball into the air using the velocity
equation. Calculate how high the throw was using the distance equation.

Procedure:

Throw a ball into the air as hard as you can making it go as straight up as
possible. This is not an ideal throwing position but will make the
calculations easier. When calculating the velocity of the throw you have to
use the properties of freefall. One p
roperty is that the ball stops at the
top of the throw

at its maximum height. Another property is that the ball
will be traveling just as fast when it strikes the ground as it was when it
was thrown. Lastly, the time taken for the ball to go from the top

to the
ground is ½ of the total time the ball spent in the air. We are going to
assume that the initial height of the throw is negligible.

Measure the time of the throw with a stop watch, from the point the ball
leaves the hand to when the ball hits the

ground.
Divide the time by 2

to
find the time it takes the ball to reach the ground from the highest point.

Use your distance equation to calculate the value
of the acceleration. SHOW ALL OF YOUR WORK!

Calculated v = ___________ m/s

Calculated height = ____________ m

Time (s)

Average time = _________

25

Write down key terms with their definitions.

Write down the equations used in the Chapter.

Solve the following example questions:

1.

What is motion relative to?

2.

Spee
d is the rate at which what happens?

3.

Explain the difference between instantaneous speed and average speed.

4.

Explain the difference between speed and velocity.

5.

Calculate the average speed of a human running 18m in 3s.

6.

Calculate the distance traveled
by the person from #5 in 30 min.

7.

Calculate the acceleration of a matchbox car that rolls down a 3m ramp
in 1.5s.

8.

Calculate the speed and the distance fallen by a ball that is dropped
from rest in the time intervals of 1second through 7 seconds.

9.

Cal
culate the height of a ball thrown upward at 12 m/s.

26

Chapter 5

Highlights:

Vector Components

Relative Velocities at Angles

Projectile Components

Horizontal Projectile Motion

Projectile Range

Calculating Projectile Velocity

Upwardly

Launched Projectiles

Key Terms

Vector

Pythagorean Theorem

Components

Resultant

Range

Projectile

Time of Flight

27

If you could run at a speed of 10 km/h for 2 hours, how far could you run
from home?

20 km?

Does running at this rate for this long tell you how far you ran from home?

No, without a reference
point you don’t know.

What would be the different possibilities for the distances traveled?

Anywhere from 0 up to 20 km.

1.

How far did you drive if you drove at 20 km/h for 1 hour north, and then
m/h for 2 hours north?

20 km + 100 Km = 120 km

2.

How did you add these together?

One right after the other

they were in the same direction.

How far did you drive if you drove at 30 km/h north for 2 hours and then
drove at 40 km/h south for 2 hours?

60 k
m

80 km =
-
20 km, the directions were opposite so you subtract the
quantities.

How far did you drive if you drove at 40 km/h north for 2 hours and then
drove at 40 km/h east for 2 hours?

80 km + 80 km = ?

80
2

+ 80
2

= d
2
,

d = 113 km

northeast

5.

How do you

you have to use pythagorean’s theorem to
figure it out because the directions are perpendicular to each other!

Vector

a magnitude (scalar quantity) with a
direction

Resultant

a vector that is the combination of 2 or more vectors

Vectors are represented as arrows. The length of the arrow indicates its
magnitude (scalar), and the tip sh
ows its direction.

28

1.

2.

7 m south + 3 m north

4 m north + 8 m north

4 m south

12 m north

3.

4.

7 m east + 8 m west

3 m north + 4 m east

1 m west

5 m northeast

Pythagorean Theorem

a math method used to add perpendicular vectors

a
2

+b
2

= c
2

Components

two perpendicular vectors that represent a single vector

Usually an x
-
comp. and a y
-
comp.

1.

2.

24 m

10 m

26 m

8 m

6 m

10 m

29

Graphically Draw the Component Vectors for each Resultant:

How fast is

the airplane going relative to the ground? The Plane flies at 100
km/h due north and the wind blows at 25 km/h whose direction is indicated by
the arrow.

W

W

W

125 km/h north

75 km/h north

103 km/h northeast

Assignment Ch.
5:1
-
5
,18
-
21
, 37, 38

30

What is a projectile?

An object traveling through the air influenced only by gravity.

What governs a projectile?

Gravity, initial velocity, launch angle

What kind of a path does a projectile form?

parabo
la

Which of these objects would be considered a projectile? Why?

Football, ball, Frisbee, airplane, balloon

Only the football and ball because the others have another force acting on
them.

Would a rocket be considered a projectile? Why?

No. it has
another force acting on it.

Which of these two objects will hit the ground first when dropped from the
same height at the same time?

Same time

property of gravity.

Demo: steel ball bearing, plastic ball

Why does this happen?

All objects fall at the
same rate without air resistance.

What would happen to the time spent in the air if these two objects were
dropped
from the same height at the same time, but one of them were initially
moving horizontally?

Nothing. Both fall the same vertical distance in the same
amount of time.

Demo;

Ball launcher and drop

Race cars off track

What direction and only direction does

gravity act?

Downward.

31

x
-
direction

(horizontal)

the horizontal velocity doesn’t change.

Range

distance covered across the ground by a projectile.

y
-
direction

(vertical)

the vertical velocity is always changing due to
gravity.

Which component determines the time of flight?

Y
-

dire
ction

x
-
component equation:

X = v
x

t

y
-
component equation:
g = 10 m/s
2

y = ½ g t
2

= 5 t
2

v
y

= gt = 10 t

v
i

= 30 m/s

Each second of fall this ball is projected
horizontally 30 m.

Examples
:

1) Using Dia. 1 as a guide, answer the following questions. Each successive
ball represents a 1 second time interval.

How long was the ball in the air?

5s

What is the range of the ball?

X = 30 (5) = 150 m

How far down did the ball fall?

Y = 5 t
2

= 5 (
5)
2

= 125 m

What is the final velocity for each ball?

V = 50 m/s; v
2

= 50
2

+ 30
2
, v = 58.3 m/s

32

Objective:

To calculate the velocity of a projectile that is fired
horizontally using the project
ile motion equations.

Theory/Procedure:

The range of the projectile is given by the equation,

X = v
x
t

Where t is the time of flight, and vx is the horizontal velocity of the
projectile. The time of flight is calculated from the main y
-
equation

H = ½ gt
2
,
where
g = 10 m/s
2
.

Height

Range

Write down which launcher you are using _____________.

Measuring the range of the
projectile

To calculate the velocity of the projectile,
you must first
measure the average range of
the projectile. Launch the projectile 10
times onto the floor and measure the range
of each launch starting from the end of the
launcher to where the projectile hits the
floor. Average the measured values.

Calculating the time of flight

Measure the distance from the bottom of the
launcher’s muzzle to the floor.

H
= ___________ m

Use your height equation from above to
calculate the time in the air.

Calculated time,
t = ___________

Launch

Range (m)

1

2

3

4

5

6

7

8

9

10

Average
Range =

33

Calculating the Initial Velocity of the Projectile

Use the range equation, the calculated time of flight, and your average range
to find the horizontal velocity (
v
x
) of the projectile.

v
x

= ____________ m/s

Questions:

1.

What would happen to the range of the projectile in this lab if the
velocity of the launcher was increased?

2.

What would happen to the time of the projectile in this lab if the
velocity of the launcher was increased?

3.

What would happen to th
e range of the projectile in this lab if the
height of the lab table was increased?

4.

Calculate the range of your projectile if the speed of your projectile
launcher is 20 m/s and the height of your lab table is 1.1 m.

34

What happens to the range of a projectile when launched at increasing angles
from the horizontal?

The range increases to 45
o

then decreases to 90
o

Demo:

hose and water

Tennis ball launcher

Launcher at angles

What pairs of angles give the same range? Why?

-

at a small angle ___
30
____

to be
90
o

V
y

component is __
small
___

time of flight is _
small
___

but the
V
x

component is __
large
__

-

at a large angle __
60
__

V
y

component is _
large
__

time of flight is _
large
__

but the
V
x

component is _
small
_

What are these angles called?
Complimentary angles

What is the angle that gives a maximum range? Why?

45
o
, Gives the largest amount of time in the air for the largest horizontal
speed.

Shooting the Monkey

Where should a hunter aim to tranquilize the monkey hanging in the tree?

A. Right above the monkey

B. In the middle of the monkey

C. Right below the monkey

Why does this work?

Both objects will fall the same vertical distance fro
m a straight line path in
the same amount of time.

Questions:

1.

A projectile is shot at an angle into the air. Neglecting air
resistance, what is its vertical acceleration? Its horizontal
acceleration?

10 m/s
2
, 0 m/s
2

2.

At what point in its path does a
projectile have minimum speed?

At the highest point

it’s all horizontal speed.

35

30 m/s

10 m/s

A toy

cannon is shot almost straight up into the air. The velocity components
of the cannon ball are given in the diagram above. If the acceleration of the
cannon ball is g = 10 m/s
2
. Each successive ball on the parabolic path
indicates a 1 second time interval
.

What are the missing velocity values indicated by the empty boxes?

What is the range of the toy cannon ball?

X = 10 m/s (6s) = 60 m

Assignment Ch.
5
:

10
a,
11
-
13
,
27, 30, 34, 40, 42
-
44

20
m/s

31.6
m/s

22.4
m/s

14
m/s

10
m/s

10
m/s

10
m/s

10
m/s

36

Write down key terms with their definitions.

Write down the equations used in the Chapter.

Solve the following example questions:

1.

How does a vector quantity
differ from a scalar quantity?

2.

Calculate the resultant of two vectors with a magnitude of 3 km and 4km
that are at right angles to each other.

3.

Calculate the resultant velocity of an airplane that flies at 100 km/h
through the air and encounters a 75 km
/h head wind. A 75 km/h tail wind.
A 75 km/h cross wind that acts at a right angle to the airplane.

4.

In the absence of air resistance, why does the horizontal component of
velocity for a projectile remain constant while the vertical component
changes?

5.

W
hat is freefall acceleration?

6.

At the instant a ball is thrown horizontally an identical ball is
dropped from the same height. Which of the two balls will hit the ground
first? Why?

7.

How far below an initial straight
-
line path will a projectile fall in 1
second? 2 seconds? 3 seconds?

37

8.

Neglecting air resistance if you throw a ball into the air with a speed
of 20 m/s how fast will it be traveling if it is caught at the same
height on its way back down?

9.

Does #8 depend on the angle with which the ball is th
rown?

10.

At what angle will a cannon ball fired from a cannon achieve
maximum height? Maximum range?

11.

What angles will give a projectile the same range?

12.

Calculate the range of a projectile that is fired with an initial
horizontal speed of 20 m/s from a buil
ding 45 m high.

13.

A toy car traveling horizontally across a table top 1m high falls
to the floor. The toy car travels a distance of 2 m across the floor.
How fast was the toy car traveling when it left the table top?

38

Chapter
3

Highlights:

Mass vs. Weight vs. Volume

Inertia

Force and motion

Net
-
Force and Equilibrium

Key Terms

Inertia

Weight

Net
-
Force

Volume

Vectors

Pythagorean Theorem

Mass

Equilibrium

Support Force

Friction

Tension Force

Newton

Normal Force

39

What is mass?

Mass is the amount of “matter” in an object?

Dem漺⁳桯瑰ut v献sball

Mass

the amount of matter in an object

Weight

the force of gravity on an object

Volume

the amount of space an object occupies

1 kg = __
2.2
_____ lb. =

___
10
_____ N

1.

Does a 2 kg iron block have twice as much
mass

as a 1 kg block of
iron? Twice as much volume? Twi
ce as much weight, when
measured at the same location?

Yes, Yes, Yes.

2.

Does a 2 kg bunch of bananas have twice as much
mass

as a 1 kg
block of iron? Twice as much volume? Twice as much weight,
when measured at the same location?

Yes, No, Yes.

3.

A 1 kg bag o
f nails weighs 10 N at the surface of the earth. What
does a 2 kg tub of butter weigh?

20 N

Assignment
Ch. 3
:

12
-
18, 23
-
27, 37, 39
-
40, 51
-
55

40

What will happen if a foam ball is thrown toward a student?

Nothing, the ball will simply bounce off.

What will happen if a
shot put is thrown toward a student?

The student would be seriously injured if done.

Why is the second situation more dangerous?

When moving, the larger mass is harder to stop moving.

Inertia

?’?Ÿ?Q? ?“?›?–?”?¥?Ï?¤?Q?£?–?¤?š?¤?¥?’?Ÿ?”?–?Q?¥? ?Q?”?™?’?Ÿ?˜?–?Q?¥? ?Q?ž? ?¥?š? ?Ÿ?Q

it is the
measure of mass.

Demos: cup and coins, paper and cups, matchbox cars on ramps, bottle
and silk sheet, coins on elbow, chalk in a bottle, film cases and paper
strip, studen
t on moving cart c
atching ball.

What is common in all of these cases?

They all had mass that did not change its state of motion.

What happened when the matchbox car rolled down the ramp? Did it
reach approx. the same height on the other side? Explain.

It rolled up the other

side. Pretty close. The force of gravity caused
it to slow down when rolling up the side.

What happened when the track turned into a flat level track? Why did
it do this?

Since there’s no force to slow it down, the car kept
traveling down the track.

䥦If
r楣瑩潮 捡n be⁩ n潲odⰠ睨a琠t潲捥⁩c ne捥c獡特⁴漠步op 慮 潢橥捴c
m潶ing?

None.

Newton’s 1
st

Law of Motion

an object at rest stays at rest, an object
in motion stays in motion until acted upon by an outside net
-
force.

Called the law of inertia

More mass

= __
more inertia
___ = __
more resistance
_

Must have an external
net
-
force to change motion

o

External force

a force acting on a separate mass.

Net

Force

the sum of all the forces
acting on an object.

41

1.

A ball is rolled across a counter top and rolls slowly to a stop.
How would Aristotle interpret this behavior? How would
Galileo?

A constant force is needed to keep an object moving. Friction
slowed the ball down.

2.

If the force of gravity between the sun and the planets suddenly
disappeared, what type of path would the
planets follow?

A straight line path at a constant speed.

3.

Is it correct to say that the reason an object resists change and
persists in its state of motion is that it has inertia?

Yes.

4.

Fill in the table:

Object

Mass

Weight

Tub of Butter

1 kg

10 N

Apple

0.1 kg

1 N

Text book

1.7 kg

17 N

Brass weight

10 kg

100 N

Large bag of Flour

5 kg

50 N

Assignment Ch.
3
:

5
-
8,
28
-
36, 38

42

Weight of student and platform together = ____________ lb.

What would be the scale reading
s

on opposite ends of the platform?

The total = the total weight

What do both scale readings measure?
The total weight

Reposition the student on the platform, what is happening with the
One goes up, the other goes down

What happens to the total of the two scale readings?

The sum stays a constant =
total weight

Can there be more than one force acting on an object?

Yes. We all have multiple forces acting at the same time.

What happens when the forces are balanced?

The forces add to be 0.

Support Force

the force supplied against weight

Normal Force

usually a support force, this force acts perpendicular
to a surface in contact with an object

Equilibrium

when two or more forces acting on an object add to be
zero.

43

1.

Calculate the net
-
force acting on the following objects:

4 N

3 N

4 N

4 N

3 N

7 N right

1 N right

3 N

5 N

2.

Calculate the missing tensions in the following diagrams that
produce equilibrium:

6 N

?

?

4 N

3 N

3 N

9 N

5 N

3.

When you step on a bathroom scale, the downward force supplied
by your feet and the upward force supplied by
the floor
compress a calibrated spring in the scale. The compression of
the spring gives your weight. In effect, the scale measures the
floor’s support force. What will each scale read if you stand on
two scales with your weight divided equally between the
m? What
happens if you stand with more of your weight on one foot than
the other?

½ your weight, one is more than the other, but both

44

4.

What happens to the tension in the strings as you increase the
angle between
the two equally supporting strings?

Tension
increases dramatically

5.

A

block has a weight of 1000 N on a weightless platform
suspended by two ropes at either end.
The tension is given in
one of the ropes. Calculate the tension in the other
rope based
on the diagrams below:

500 N

?

500 N

750 N

?

250 N

150 N

?

850 N

1000 N

?

0N

Assignment Ch.
2:

1
-
3, 9, 14, 15, 33
-
35, 42
-
46

45

Chapter
6

Highlights:

Force and Acceleration

Newton’s 2
nd

Law

Friction

Air Resistance and Terminal Velocity

Pressure

Key Terms

Force

Acceleration

Mass

Inertia

Friction

Terminal Velocity

Pressure

Pascal

46

Video clip: dodge neon vs. viper

Which of these cars wil
l win this drag race?

Why?

Dodge neon due to its smaller mass.

What causes changes in speed?

An unbalanced force.

How do you know if you are being accelerated?

You can feel the effects of

your body will change its position.

Mass

(Newton’s def.)

inertia, an object’s resistance to changes in
motion.

1
st

part

acceleration is

inversely proportional to an object’s mass

an
increase in mass decreases acceleration.

Demo: students on cart w/ changing mass

2
nd

part

acceleration

is directly proportional to the applied net
-
force

an increase in force will increase acceleration.

Demo: students on cart w/ changing force

Newton’s 2
nd

Law of Motion

the acceleration of an object is = the net
-
force
divided by the object’s mass.

a =
F
net
/m

Find the mass of a student.

1.

Find the force of friction ___________
N

2.

C
alculate the student’s acceleration. Measure distance and time when
pulling with 40 N of force.

3.

Calculate the student’s mass.

47

1.

If a car

can accelerate at 2 m/s
2
, what acceleration can it attain if it
is towing another car of equal mass?

1 m/s
2

2.

What kind of motion does a constant force produce on an object?

Constant acceleration.

3.

Fill in
the missing values in the table:

Force

Mass

Acceleration

100 N

2 kg

50 m/s
2

50 N

5 kg

10 m/s
2

200 N

10 kg

20 m/s
2

250 N

50 kg

5 m/s
2

480 N

120 kg

4 m/s
2

Do Lab: Proving Newton’s 2
nd

Law

Assignment Ch. 6
:

1
-
7,

22
*
,25
-
28,56
*
calculate the forces and
acceleration

48

m
F
a

2
2
1
at
d

P
rove Newton’s 2nd Law by parts.

Newton’s 2nd Law consists of 2 parts.

Part 1) The acceleration of an object is inversely proportional to the mass
of the object.

a

1/ m

The first part predicts that an increase in mass, for a
constant applied
force, will result in a decrease in acceleration.

Part 2) The acceleration of an object of constant mass is directly
proportional to the force applied to that object.

a

F

The second part predicts that an increase in force, for a co
nstant mass, will
result in an increase in acceleration.

Combining the two parts together results in Newton’s 2
nd

Law equation:

The equation used to calculate the cart’s acc
eleration comes from equation
:

distance = d = _________

150 g mass

F
g

49

Friction needs to be overcome in this lab before measuring any
quantities. Friction can be compensated by adding a lit
tle bit of extra mass
to the end of the pulley. The amount of mass should be enough to keep the
cart moving at a constant velocity across the tabletop. If you see the cart
increase in speed then too much mass was added to the end of the string. Add
this ma
ss to the
hangar at the end of the string.

Mass and Acceleration

T
he constant force used to accelerate the lab cart will be provided through
the pull of gravity on the masses at the end of the string. The amount of
mass should be 150 g
(0.15 kg)
and constant so that it will be enough to
accelerate the cart within reason.

This mass is in addition to the mass used
to overcome the friction.

Mass is the variable in this part so that is what will be manipulated to see
what will happen to the time to cover a measured distance. The mass will be
increased by stacking 500g
(0.5 k
g)
masses on top of the cart each interval.
Record the total mass of the system in the chart below for each of the
trials. Measure the distance covered, and record the time the cart took to
cover that distance. Be sure to stop your timing when the masses h
it the
floor and NOT when the cart reaches the end of the table. Practice timing the
cart first until you have a consistent time and record the value. The cart
should NEVER hit the pulley

this causes damage to the cart and pulley.

50

Trial

Total mass

Time

1

Time

2

Time 3

Ave.
Time

Acceleration

1

2

3

4

5

6

7

Analysis
:

Show your calculations and fill in the table above:

After completing the table, plot the data points “Mass vs.
Acceleration”
on
the computer
and find the best fit graph for your data. Attach each of the

51

1.

What kind of graph do you get from “Mass vs.
Acceleration
”? Does this

2.

aight line or a curve?

3.

Based on the curve fit of your graph, could your acceleration ever be 0?

4.

Does the acceleration of your cart increase or decrease with an increase
in mass? Explain why.

Force and Acceleration

Place
2

kg on your lab cart along with the set of
6

20g
brass hangar
masses. This will be the constant mass of your system. Record the total mass
of the cart and masses.

Mass = ___
2880
__________
g

The pulling force will be the variable in this part of the lab. The force is
increased each interval by taking one of the 20 g

brass masses off of the
cart and placing it on the hangar at the end of the string.

Be sure to
convert the grams into Newtons.
1 g = 0.01 N

The acceleration will be calculated using your distance equation and your
average time just as in part 1 of the l
ab. Be sure to stop your timing and
the cart when the masses hit the floor!

52

Trial

Force

Time

1

Time

2

Time 3

Ave.
Time

Acceleration

1

2

3

4

5

6

7

Analysis
:

Show your calculations and fill in the table
above:

After completing the table, plot the data points “
Force

vs.
Acceleration”
on
the computer and find the best fit graph for your data. Attach each of the

53

5.

What kind of graph do you get from “
Force

vs.
Acceleration
”? Does this

6.

Is your graph a straight line or a curve?

7.

Based on the fit of your graph, what i
s the slope of the graph? Compare
it to the total mass of part 2. What do you find?

8.

Does the acceleration of your cart increase or decrease with an increase
in force? Explain why.

54

What happens when this desk is slid across the floor?

It will eventually stop.

Why does it stop?

A frictional force between the desk and the floor.

Friction

(F
fr
)
a contact force between surfaces that opposes sliding
motions.

Does not depend on the contact area

It is only determined by two factors

What do we use fricti
on for? Can we live without it? Discuss.

Walking, sitting, stopping, etc. No, we need friction to do many things.

What creates friction?

Friction is created by the interlocking of microscopic fissures in the
surfaces.

What happens to the amount of frictio
n when a sheet of paper is held loosely
vs. tightly?

Tighter creates more friction

the fissures interlock harder.

What happens to the amount of friction when a sheet of paper is held with
wood blocks vs. rubber stoppers?

The rubber has flexible fissures

that will
fit into the fissures of the other easily.

What determines the amount of friction?

1.

The normal force between the surfaces.

2.

The types of materials in contact.

What can we do to reduce friction? (3 basic ways)

Lubrication

fills the fissures so they can’t interlock,
make the surfaces
as smooth as possible

reduces the size of the fissures,
use wheels

makes
sliding motion into a
rotational

motion.

Is there another kind of friction other than friction
from surfaces
?

Yes. Air friction, or fluid friction.

55

What happens when a sky diver pulls the rip
-
cord?

Air resistance increases.

Why does it do this?

Air resistance increases with the cross
-
sectional area of an object.

Air resistance

a frictional force caused by the movement of an object
through a fluid (air)

Also called ___
drag
___.

What determines the amount of air resistance?

The shape and cross sectional area

also air density but that can’t
be
changed.

How do you increase the amount of air resistance? When is this beneficial?

Make a cup shape as large as possible. Skydiving, drag racing, slowing down
the space shuttle.

What about the opposite of this?

A tapered tear
-
drop shape is the most ae
rodynamic shape.

Demo: ping
-
pong ball, parachute, dragster, space shuttle, paper balls

Terminal Velocity

the speed at which the weight of the object is equal to
its air resistance

the object no longer accelerates.

Video clips:
sky diving

1.

Two forces act on a

book resting on a table: its weight and the support
force from the table. Does a force of friction act as well?

What if the
table is tilted slightly so that the textbook still does not move?

No. There are no forces acting horizontally that want to move th
e textbook.

Yes. There is a force acting to pull the textbook sideways which is counter
-
acted by a frictional force.

2.

Suppose a high flying jet cruises with a constant velocity when the
thrust of its engines is a constant 80,000 N. What is the acceleration
of the jet? What is the force of air resistance acting on the jet?

A = 0 m/s
2
-

constant vel. Air resistance = 80,000 N

Assignment Ch. 6
:

8, 9, 16
-
20, 32, 52
, 67

56

Why doesn’t a person get harmed while lying on a bed of nails?

The person’s weight is distributed to each nail which is not enough force to
cause the nail to pierce skin.

Pressure

(Pa
scals

N/m
2
)

the force per unit area

American units = lbs./in
2

P =
F / A

What is the pressure exerted on the floor by a person standing straight up?

What is the pressure exerted on the floor by a person lying down?

What is the pressure exerted on
the floor by a person standing in high heels?

Atmospheric Pressure

(14.2 lbs./in
2

~ 98,500 N/m
2
)

fluid pressure due to the
weight of the air.

Video clips:
c
an crush, tanker crush

1.

How much force is being exerted on an area of 36 in
2

by a pressure of
90lb./in
2
?

3240 lb.

2.

The roof of a building is designed to withstand 14,000
N

of force. The
roof of a building is 10 m long, and 5 m wide. What is the least amount
of pressure the roof must hold?

280 Pa

Due Activity: How much does your car weigh?

Assignment Ch.
6: 10
-
12, 24,
42, 43

57

Every car is supported by tires that are inflated with a specific amount of
air pressure. The air

pressure supports the car on the ground over a certain
contact area. By measuring the contact area, called the foot print, and
measuring the pressure of each tire, you can calculate the weight supported
by the tires.

Calculate the weight supported by one

of the front tires first:

Measure the width of tire tread = ___________ in.

Measure the length of the contact area by shoving two sheets of paper on
either side of the tire until they hit the where the tire contacts the
ground. Length of tire tread = __
________ in.

Measure the tire pressure using a tire gauge. Pressure = ___________ lb./in
2

Be sure to subtract the normal atmospheric pressure of 14.2 lb./in
2

that
amount of pressure is already balanced before filling the tire.

Calculate the weight suppo
rted by the tire:

(then x 2, two front tires)

Repeat this procedure for one of the rear tires:

Calculate the total weight of the car and compare it to the actual weight
listed on the driver door or from the manufacturer online. Compare the
results

explain any differences.

58

Write down key terms with their definitions.

Write down the equations used in the Chapter.

Solve the following example questi
ons:

1.

What are the two parts to Newton’s 2
nd

Law?

2.

What does Net
-
Force mean?

3.

What are the two equilibrium conditions?

4.

What does adding mass to an object do to its acceleration? Explain why.

5.

Calculate the Net
-
Force acting on these objects, and then find

their
accelerations.

a.

b.

20 N

15 N

15 N

10 N

30 N

10 N

55 N

6.

If a net
-
force on an object is tripled what will happen to an object’s
acceleration?

20 kg

15 kg

59

7.

If a mass is dumped on an object that triples
the objects mass what will
happen to the object’s acceleration?

8.

What happens to the value of an object’s acceleration while falling in
the presence of air resistance?

9.

A jet with a mass of 10,000 kg is accelerating at what value when each
of its 2 jet eng
ines produces a thrust of 7500N.

10.

When the jet from #9 is cruising at a constant velocity and
altitude with the jet engines running as stated. What is value of the
jet’s air resistance?

11.

What effect do snow shoes have in the winter? Why do they work?

12.

A tire has a standard pressure of 32 lbs./in
2
. If the foot print
of the tire on the ground is 5in. x 7 in. How much weight is this tire
supporting? If all tires are the same how much does this car weigh?

60

Chapter
7

Highlights:

Action
-
Reaction Pairs

Rockets

Key Terms

Interaction

Action
-
Reaction

Mass

Force

61

How does a rocket work?

Newton’s 3
rd

law.

What happens when a blown up balloon is released? Why does it do that?

The balloon pushe
s the air out, the reaction is the air pushes back on the
balloon. Due to the air’s
inertia (
mass
)
.

What will happen to the students given these different situations?

They do in opposite directions with equal force.

Demos: 2 students pushing and pulling

with different masses

Mass

(Newton’s definition)

inertia

Which is an object’s resistance to change in motion

o

More mass =
more inertia

=

more resistance

When the students were on the carts:

Action:

Reaction:

Were they the same force?

Yes. Forces
always come in pairs.

Newton’s 3
rd

Law of Motion

for every action force there is an equal but
opposite reaction force.

Force only exists when matter is present and requires 2 separate masses

they compose an
interaction pair

Ex.

The students make up an interaction pair. To find the reaction force from
the action force, just switch the terms of the objects. (Note: there is no
difference between action
-
reaction forces

they are indiscernable)

62

Ex.

Action: The Earth pulls on a ball
.

Reaction:
the ball pulls on the earth.

Action: You walk by pushing on the floor.

Reaction:
the floor pushes on you.

Action:

Reaction:

Application to Newton’s 2
nd

Law:

What happened to the acceleration when the mass of one student was doubled?

The
acceleration was decreased by half.

Force on student 1 = Force on student 2

F
1

= F
2

F
1

m
A

=
M

a

Shooting a cannon:

Action:

Cannon pushes on ball.

Reaction:
ball pushes on cannon
*

*
Sometimes called recoil

F
2

Calculate the acceleration of the cannon

if the mass of the cannon ball is
5kg and accelerates at 1200 m/s
2
, and the cannon has a mass of 100 kg.

5 (1200) = 100 a

a = 60 m/s
2

63

1.

Does a stick of Dynamite contain force?

No. it contains energy. The release of this energy create
s a force on its
surroundings.

2.

A car accelerates along a road. Strictly speaking, what is the force
that moves the car?

The road pushing on the tires.

3.

We know that the earth pulls on the moon. Does the moon also pull on the
earth? If so, which pull is
stronger?

Yes. It is the same amount of
force. The earth doesn’t really move much due to its mass being much
larger than the moon’s.

4.

Suppose a friend who hears about Newton’s 3
rd

law says that you can’t
move a football by kicking it because the reaction force by the kicked
ball would be equal and opposite to your kicking force. The net
-
force
would be zero, so no matter how hard you kick, the ball won’t move.
What is wrong with thi
s logic?

The force of your kick is acting on
separate masses, not the same mass. The net
-
force would be zero if it
were acting on the same mass but it isn’t.

Assignment Ch.
7:
1
-
11, 13, 14, 18, 24, 25, 28
-
30, 34
-
41, 54, 55

64

Chapter
8

Highlights:

Momentum

Impulse

Elastic and Inelastic Collisions

Law of Conservation of Momentum

Key Terms

Momentum

Impulse

Elastic

Inelastic

Vectors

Conservation of Momentum

65

Which would you rather do: try to catch a foam ball, or a shotput? Why?

Foam ball, it has less mass.

Which would you rather do: try to catch a foam ball thrown slowly or one that
is pitched? Why?

the
slow one. It has less motion.

Newton’s 1
st

Law of Motion

(inertia)
-

object at rest stays at rest, an
object in motion will stay in motion, unless acted on by an outside net
-
force.

Momentum

(
kg.m/s
)
-

describes inertia in motion, it is the product of mass
moving at a certain velocity.

= m v

Is momentum a vector?

Yes. Velocity is a vector so momentum is a vector.

Interpreting the equation;

Can a motorcycle have the same momentum
as a full size car? Explain your

Yes. If the motorcycle is moving much faster than the car or they are
both at rest.

In order to change the state of motion of an object what must be applied?

Force.

If the driver were to apply the gas lightly to ac
celerate up to 60 mph how
long would it take?

It would take a long time.

If the driver in the previous question slammed on the gas to accelerate up to
60 mph, how long would the car take?

It would take a short time.

Did the car undergo the same change in

momentum in each of the previous
cases?

Yes. The momentum change was the same.

66

Impulse

(
kg.m/s
)

change in momentum, it is the product of net
-
force and
time acting on an object.

J =
F t

Is impulse a vector?

Yes. Force is a vector so impulse is a
vector.

Use the equation to describe the accelerating car situation:

A large force in a short period of time = a small force in a long period of
time.

Application and interpretation of

the equation
:

A desk sliding across the floor at 3 m/s slowly slides to a stop due to
friction. How long would the desk take to stop? How much force was acting on
the desk as it slid to a stop?

If the same desk were to stop by striking a wall, how
long would it take for
the desk to stop? How much force acted on the desk?

Explain the differences and similarities in the previous example using
impulse and momentum:

Explain the momentum and impulse applications in the following demos:

Boxing, Air ba
gs, Car safety, jumping off a platform, hammer on a nail.

Short impact time results in a large impact force. A longer impact time
results in a smaller impact force.

67

1.

Calculate the momentum of a 1000 kg car moving at 20 m/s.

20,000 units

2.

If a 5 kg shotput is to have the same momentum as the car in the
previous problem, how fast must it be
traveling?

20,000 = 5 v, v = 4000 m/s

3.

If a motorcycle, with a mass of 300 kg were to have the same momentum as
the car in #1, how fast must it be traveling?

20,000 = 300 v, v = 67 m/s

4.

What impul
se is needed to get the car from #1 moving at 20 m/s if it
s
tarted from rest?

20,000 units

5.

What imp
ul
se is needed to stop the car from #1?

-
20,000 units

6.

If you wanted to stop the car in 10 sec. How much force must the tires
supply? What is the origin of this force?

F t = 20,000, F = 2000 N, the frictional force
tires.

7.

If the car were to suddenly stop, as in a car accident, in ½ second.
How much force acted on the car? What happens to a car in an accident?

F t = 20,000, F = 40,000 N, the tremendous force causes the car to crumple.

8.

If an airba
g increases the time of impact 5 times as much as without an
airbag, how much will an airbag decrease the force of impact?

5 times.

9.

If a dish falls, will the impul
se be less if it lands on a carpet than
if it lands on a tiled floor? Which one will most li
kely cause the dish
to break? Explain.

Same impulse. The tile floor

less time of impact.

Assignment Ch. 8
:

1
-
7, 9
-
11, 24
-
27, 35
-
46

68

Applications of Impulse and Momentum
:

How do martial arts experts break wood with their bare hands?

Quick hands decrease

the time of impact which increases the force of impact.

Demo: board breaking

Impulse

change in momentum.

Momentum

inertia in motion.

What happens when a concrete cinder block is struck by a fast moving sledge
hammer?

It breaks due to the
large
momentum transfer

and short impact time.

Demo: bed
-
o
-
nails

Why is it important that the concrete block have such a large mass?

The large mass resists the sudden change in motion due to the sledge hammer
and doesn’t move as much before breaking apart.

What

is the impact time when doing either of these two demonstrations?

Impact time is short.

What does this tell you about the impact force?

Large impact force.

Is the impulse the

same on the boards as on the hand?

Yes.
By Newton’s 3
rd

law and the time of impact being the same for both.

Is the impulse the same on the block as it is on the hammer?

Yes. Same reason as above.

69

What is the difference between elastic and inelastic collisions?

Bouncing.

Elastic

objects col
lide and bounce apart

there is a transfer of momentum
between the objects which results in a larger impulse.

Inelastic

objects collide and stick together

the momentum is shared
be
tween the masses.

What happens

to the impulse when an object
has an
inelastic vs. elastic
collision?

Impulse is smaller in inelastic collisions.

Bouncing does not necessarily increase impact force, it involves
stopping and pushing back in the opposite direction.

Demo: exercise ball

Assign
ment Ch. 8
:

12
-
14, 17, 47

70

What will happen to the velocities of the students after each of the
collision interactions?

Inelastic collisions result in a slower velocity.
Elastic collisions result in the same or
higher velocity.

Demo: students on carts with different mass

elastic and inelastic collisions

Law of Conservation of Momentum

the total momentum before a collision or
interaction must be equal to the total afterwards.

No external forces acting on the

system

Elastic Collisions

momentum is exchanged between the objects

Demo: steel pendulums, rubber ball

Inelastic Collisions

momentum is shared between the objects

Demo: catching rubber ball, playdoe glob

Examples:

Calculate the velocities of the
two

car

system after the following
collisions:

1.

v = 10 m/s

v = 0 m/s

1000 kg

2000 kg

inelastic collision

10,000 + 0 = 3000 v

V = 10,000/3000 =
3 1/3 m/s

71

2.

v = 10 m/s

v = 0 m/s

v = 2 m/s

v =
?

m/s

1000

kg

2000 kg

elastic collision

10,000 + 0 = 1000 (2) + 2000 v

10,000

2000 = 2000 v

8,000/2000 = v = 4 m/s

v = 10 m/s

v =
?

m/s

v =
0

1000

2000 kg

inelastic collision

10,000

2000 v = 3000
(0)

2000 v = 10,000, v = 5 m/s

A train car with
a mass of 5000 kg is traveling to the right with a
velocity of 5 m/s. It collides with two other connected cars of equal
mass at rest. If they collide and stick together, what is their final
velocity?

5000 (5) + 10,000 (0) = 15,000 v

25
,
000 = 15,000 v, v
= 1.7 m/s

What is the change in momentum of each car in example #2? Are they the same?

8,000 units for each. The momentum lost by one was
gained by the other.

Assignment Ch. 8
:

15, 16, 18, 50, 55
-
58, 60
-
62

72

Write down key terms with their definitions.

Write down the equations used in the Chapter.

Solve the following example questions:

1.

What two quantities are involved in
calculating momentum?

2.

Can a car have the same momentum as a motorcycle? Explain.

3.

What two quantities are involved in calculating impulse?

4.

Why should a boxer ride with the punch? Why should the boxer try not to
move forward into an oncoming punch?

5.

Why are cars designed with airbags, crumple zones, padded dash boards,
and stretchy seat belts? Explain using impulse and momentum change.

6.

If impact time is increased 3 times what happens to the value of the
impact force?

7.

If an applied force on a cart
acts for 4 times longer than before, what
happens to the value of the cart’s final momentum as compared to