1. Newton’s Laws of Motion
Isaac Newton
(1642 – 1727)
Newton’s Laws of Motion

2. or anything else that has the ability to change motion.
What is a Force?
Force can be defined as a
or a
or anything else that has the ability to change motion.

3. In SI units, a force is measured in newtons (N)
In SI units, a force is measured in newtons (N). One newton is about the amount of force it takes to lift a quarter-pound cheeseburger.

4. How do you figure force? Force = mass x acceleration F = m • a newton
Newton (N) (kg) (m/s2 )
Easier than saying kilogram  m/sec2
newton

5. You must understand the difference between
To Understand Force…
You must understand the difference between
Mass
Weight
2 Kg Mass
AND

6. What is Mass? Mass is measured in kilograms.
The amount of “matter” in an object.
1 Kg
Mass
1.5 Kg
Mass
2 Kg
Mass
Mass is measured in kilograms.

7. How is Mass Different Than Weight?
Weight is mass times the force of gravity
Weight is a measurement of FORCE.
9.8 N
14.8 N
19.7 N
(1 kg x 9.86 m/s2)
F=ma
(1.5 kg x 9.8 6m/s2)
(2 kg x 9.86 m/s2)
Acceleration due to gravity (9.8 m/s2)
Acceleration due to gravity (9.8 m/s2)
Acceleration due to gravity (9.8 m/s2)
1.0 Kg
Mass
1.5 Kg
Mass
2.0 Kg
Mass
How can you measure force?
Calculate mass x acceleration.

8. Being pulled by different gravity? Your weight may be different.
100 Kg
Mass is
220 lbs
Being pulled by different gravity? Your weight may be different.
However, your mass never changes.
On the Moon 220 lbs. would weigh 35 lbs.
On the Sun 220 lbs. would weigh 5,956 lbs.
On Mars 220 lbs. would weigh 82.9 lbs.
What’s “Your Weight On Other Worlds?”

9. Let’s look at Newton's three laws of motion...
Isaac Newton is the first scientist responsible for formulating laws regarding motion.
These laws explain why objects move (or don't move).
Let’s look at Newton's three laws of motion...

10. Newton's 3 Laws
An object will remain at rest unless acted upon by an “unbalanced” force. An object in motion will continue with constant speed and direction, unless acted on by an unbalanced force. 1
This law shows how force, mass and acceleration are related as shown in the equation below:
Force = mass x acceleration 2
For every action force there is an equal and opposite reaction force. 3

11. Inertia Newton’s First Law: Balanced Forces This is known as
An object will maintain a constant state of motion. (Speed and direction remain unchanged)
This means an object at rest tends to stay at rest
and
an object in motion continues in the same direction with the same speed.
Balanced Forces
This is known as
Inertia
Stay at rest: a book on a table
Stay in motion: a bowling ball tossed in space
It will go on and on forever.
Table pushes up on book
Science
Gravity pulls down on book

12. Newton’s First Law: Unbalanced Forces Force of friction stops the book
An unbalanced force is a force that changes the motion.
The book below slides and then stops because of a resistant force called friction. Friction is force that opposes motion.
In space there is no resistance to cause friction, so a bowling ball would stay in motion…
unless another
object got in
the way
Force of friction stops the book
Science

13. What causes friction? There are two factors which affect
friction between two surfaces:
Kind of surfaces in contact (rough or smooth)
Amount of force pressing the surfaces together
The rougher the surface and the
stronger the force between the
surfaces, the greater the amount of
friction.

14. Of course “frictional” force happens on Earth...
but, if you weren’t wearing a safety belt
you would continue your motion…
Don’t let this happen to you! BUCKLE UP!!!!

15. There are 4 types of friction
1) Static friction:
friction between two surfaces which are not moving past each other
Example: trying to move a box and it will not move

16. There are 4 types of friction
2) Sliding friction:
occurs when a force is great enough to overcome the static friction
Example: two people create enough force to make the box move

17. There are 4 types of friction
3) Rolling friction:
the friction which enables wheels to turn and objects to move

18. There are 4 types of friction
4) Fluid friction:
occurs when an object moves through a gas or liquid

19. Let’s see how Newton’s First Law of Motion applies to the NFL
3:52

20. F = ma F = ma 120 kg Lineman 100 kg Center
Newton’s Second Law: Force = Mass X Acceleration
Force and acceleration are related.
120 kg Lineman
100 kg Center
F = ma
F = ma
Scenario # 1
Look at the situation above. If the acceleration 3 m/s2 from the snap was equal between these players, then who would have the advantage of force?
Lineman = 3 m/s2 x 120 kg is 360 N
Center = 3 m/s2 x 100 kg is 300 N
The Lineman has the advantage.
Scenario # 2 Now, let’s say the Center has a 1 m/s2 advantage over his opponent at an acceleration of
4 m/s2 from the snap. Now who has the advantage of force?
Lineman = 3 m/s2 x 120 kg is 360 N
Center = 4 m/s2 x 100 kg is 400 N
Now, the Center has the advantage.

21. Solving Force Problems
Step 1 Read the problem. Draw a picture.
Step 2 Write down what you know. What are you trying to find?
Step 3 Set up the formula.
Step 4 Plug-in the numbers. Solve.

22. “How much force is needed to accelerate a 1400 kg car 2 m/s2? ”
Consider the problem…
“How much force is needed to accelerate a 1400 kg car 2 m/s2? ”
Step 1 Read the problem. Draw a picture.
1400 kg car
2 m/s2
Formula
Plug-in
Answer
F =
m =
a =
Units, units, units!

23. ? “How much force is needed to accelerate a 1400 kg car 2 m/s2? ”
Step 2 Write down what you know. What are you trying to find?
1400 kg car
How much force?
2 m/s2
Formula
Plug-in
Answer ?
F =
1400 kg
m =
2 m/s2
a =
Units, units, units!

24. “How much force is needed to accelerate a 1400 kg car 2 m/s2? ”
Step 3 Set up the formula.
F = m x a
Formula
Plug-in
Answer ?
F =
1400 kg
m =
m x a
a =
2 m/s2

25. ? “How much force is needed to accelerate a 1400 kg car 2 m/s2? ” 2800
Step 4 Plug-in the numbers. Solve.
2800
kg x m/s2 or N for newtons…it’s easier to write!
Formula
Plug-in
Answer ?
F =
1400 kg
m =
F = ma
a =
2 m/s2
1400 kg x 2 m/s2
2800 kg x m/s2
Units, units, units!

26. HELPFUL HINTS:
a = F / m
F = m x a
m = F / a F M A

27. There are 2 kinds of forces
1) Normal force:
the force a surface exerts on an object that is pressing on it

28. There are 2 kinds of forces
2) Net force:
the sum of two or more forces on an object

29. Let’s see how Newton’s Second Law of Motion applies to the NFL
3:52

30. Newton’s Third Law: Action Forces = Reaction Forces
For every action there is an equal and opposite reaction.
Look at the picture below:
What is the action?
What is the reaction?
As the gases push downward out of the rocket,
The rocket is pushed upward by gases.

31. Let’s see how Newton’s Third Law of Motion applies to the NFL
4:13

32. Newton's 3 Laws Review
An object will remain at rest unless acted upon by an “unbalanced” force. An object in motion will continue with constant speed and direction, unless acted on by an unbalanced force. 1
This law shows how force, mass and acceleration are related as shown in the equation below:
Force = mass x acceleration 2
For every action there is an equal and opposite reaction. 3

33. The Story of Newton’s Apple
Newton sat under an apple tree, and an apple fell on his head.
That falling apple gave him a revelation
and led him to describe a force called
GRAVITY.
But DON’T think of gravity as falling…
It is the pull (force) that an object has on another object.

34. Gravity is the force that ALL objects in the UNIVERSE exert between each other...
Newton said that gravitational force depends on 2 things:
The DISTANCE of the objects
The MASS of the objects
More Fg
Less gravitational force compared to...
Less Fg
The blue objects have more gravitational force between them than the green objects. This is because the blue objects have more MASS.
more gravitational force here