Laws of Motion

1
Laws of Motion
In the 1600s, Isaac Newton stated three rules
explaining how all objects move. These rules
have never been proved wrong. They are known as
the Three Laws of Motion.
2
Changing Motion
What are the only two positions an object can be
in?
An object can be in motion or at rest.
Whats the only way you can change an objects
position from being at rest or in motion?
You have to put a force into the object.
3
Review First Law of Motion
Objects at rest will stay at rest.
Objects in motion will stay in motion, in a
straight line at a constant speed.
until some force acts on them.
4
First Law of Motion
On Earth
What force makes all objects slow down or stop?
Friction
In space
What force makes objects slow down or stop?
None
5
Inertia
The first law of motion is also called the law of
inertia.
Have you ever tried to push a heavy object like a
car?
When did you have to use the most force when
pushing this object?
You should have used the most force when you were
trying to get the car to start moving. Once the
car started moving you should have used less
force. You should have used a lot of force to
stop the car.
6
What objects have inertia?
All objects have inertia.
The more mass the object has, the more inertia it
has.
7
Review First Law of Motion

• Whats an object at rest?
• What can change an objects speed or direction?
• What objects have inertia?
• What are two common examples of the First Law?

8
Second Law of Motion Page 94 Question What
two factors give an object its force?
OBJECTIVE Students will be able to define and
give common examples of the Second Law of
Motion. VOCABULARY Second Law of Motion
9

• Write these questions onto page 94
• SKIP ONE LINE BETWEEN EACH QUESTION
• Why would one object have more force than
  another object?
• What is the metric unit for force?
• What is the equation for the second law of
  motion?

10
Second Law of Motion
What would have more force?
A toy car moving 2 km/hour or a real car moving
the same speed?
Why?
The real car has more mass?
11
Second Law of Motion
What would have more force?
A car moving 10 km/hour or the same car moving
the 130 km/hour?
Why?
The fast car has more acceleration.
12
Second Law of Motion
The amount of force that an object has can be
calculated using a simple equation.
Remember, force is measured in Newtons (N.).
Make sure your answer always has this unit in the
answer.
Force mass acceleration or F ma
13
Sample problem 1
What is the force of a 4 kg. bowling ball
accelerating 3 m/sec2?
Force mass acceleration or F ma
Force 4 kg. 3 m/sec2
4 3 12 and the unit for force is (N). So the
answer is 12 (N).
14
Sample problem 2
What is the force of a 200 kg. train accelerating
40 m/sec2?
Force mass acceleration or F ma
Force 200 kg. 40 m/sec2
200 40 8,000 and the unit for force is
(N). So the answer is 8,000 (N).
15
Problem 3 Try this yourself
What is the force of a 100 kg. football player
accelerating 4 m/sec2?
Force mass acceleration or F ma
Force 100 kg. 4 m/sec2
100 4 400 and the unit for force is (N). So
the answer is 400 (N).
16
Second Law of Motion Review page 94 Write the
answers to these questions into your notes.

• Why would one object have more force than another
  object?
• What is the metric unit for force?
• What is the equation for the second law of
  motion?

17
VOCABULARY
Second Law of Motion- the force of an object
depends on its mass and its acceleration.
18
(No Transcript)
19
(No Transcript)
20
(No Transcript)
21
(No Transcript)
22
(No Transcript)
23
(No Transcript)
24
(No Transcript)
25
(No Transcript)
26
(No Transcript)
27
(No Transcript)