1. Isaac Newton
(1642 – 1727)
Newton’s Laws
The Father of Force

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

3. N What is Force? Force = mass x acceleration newton F = ma
Newton (N) (kg) (m/s2 )
newton
Easier than saying kilogram  m/sec2 N
Is even easier!

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

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

6. 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 or use a spring scale.

7. Being pulled by different gravity? Your weight may be different. 7
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 5956 lbs.
On Mars 220 lbs. would weigh 82.9 lbs.
What’s “Your Weight On Other Worlds?”

8. 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...

9. 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

10. Inertia Newton’s First Law: Balanced Forces This is known as
An object will maintain a constant state of motion. This means an object in motion continues in the same direction with the same speed
and
an object at rest tends to stay at rest
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
IP&C
Gravity pulls down on book

11. Newton’s First Law: Unbalanced Forces
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…
It kind of reminds me of a few movies I’ve seen
lately...
Force of friction stops the book
IP&C

12. Of course “frictional” force happens on earth...
but, if you weren’t wearing a safety belt
you would continue your motion…
Do not let this happen to you; buckle up!

13. 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 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.

14. 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.

15. “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
How much force?
2 m/s2
Formula
Plug-in
Answer
F =
m =
a =
Units, units, units!

16. ? “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
2 m/s2
Formula
Plug-in
Answer ?
F =
1400 kg
m =
2 m/s2
a =
Units, units, units!

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

18. ? “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
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!

19. Be sure to do the problems.
Helpful Hints:
a = F / m
F = m x a
m = F / a

20. The unit for force: 1 kg x m/s2 = 1 newton or 1N newton
Which one would you rather write for your answer?
2800 N
…I thought so.

21. 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.

22. 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 there is an equal and opposite reaction. 3

23. Results in an earthquake.
Forces and Geological Processes…
Most of the time the Earth’s massive plates push on each and move very slowly.
But, sometimes a massive plate exerts a greater amount of force that accelerates another plate.
Results in an earthquake.
To learn more about earthquakes:
Gravitational Force and waterfalls
Results in erosion

24. 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.

25. 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.

26. F=ma should be rewritten as Fg = m x g
The acceleration due to gravity is known as “g.”
When calculating FORCE due to gravity…
F=ma should be rewritten as
Fg = m x g

27. Fg = Fg
Why is the apple pulled toward the Earth rather than the Earth pulled toward the apple?
Why doesn’t the Earth move towards the apple?

28. Acceleration of Apple Is greater than Acceleration of the Earth
The apple moves faster toward the Earth than the Earth moves toward the apple.
Gravitational force (Fg) being equally exerted…
ma = ma
The apple has very little (m) mass
compared to the Earth (m).

29. The pull of gravity keeps satellites orbiting around the Earth.
The moon is a satellite too..
The pull of gravity keeps satellites orbiting around the Earth.

30. The moon does the same thing.
Satellites are sent away and placed in the exact spot where the Earth’s gravity pulls them into a “continuous free fall” or orbit... 29
The moon does the same thing.
The Earth is round and the satellite continues to “just miss” entering into the Earth’s atmosphere.

31. Does the moon’s gravitational pull affect the Earth?
Yes, the moon’s gravity is large enough to actually pull water out of the ocean from space…
Well, not quite that much...just enough to create motion of the tides.

32. Newton is even credited with inventing
CALCULUS.
Needless to say, Newton was very important in shaping our understanding of science.