1. Section 1 – Laws of Motion
Chapter 11: Forces
Section 1 – Laws of Motion

2. I did NOT “create” the laws of motion! I merely identified them!
Isaac Newton
There are “laws” that govern the motion of objects in the universe.
Isaac Newton was the scientist who identified gravity the laws of motion.
I did NOT “create” the laws of motion!
I merely identified them!

3. Newton found 3 laws of motion that are true throughout the universe.
Newton’s First Law of Motion:
Objects at rest will remain at rest, and objects in motion will remain in motion, unless an unbalanced force acts on them.

4. Something makes them move faster or slower.
The 1st Law of Motion
In OTHER words…
Objects that are sitting still will stay still, and…
Objects that are moving will keep moving until…
Something makes them move faster or slower.

5. Newton’s 1st law can be described with one word: inertia.
Definition: inertia – the tendency of an object at rest to remain at rest OR
the tendency of a moving object to keep moving.

6. If you were in outer space, and you threw a baseball…what would happen to it?
It would keep moving in a straight line forever!
At least, until an unbalanced force acted on it…

7. Mass is a measure of inertia.
Inertia describe an object’s resistance to change motion.
Which would be more difficult to push?

8. Inertia increases as mass increases.
Even if the two vehicles are moving at the same speed, the truck would be more difficult to stop because it has more inertia.

9. Newton’s 2nd Law Newton’s Second Law: F = ma
The unbalanced force acting on an object equals the object’s mass times its acceleration.
F = ma
Definition: Newton – the SI unit used to measure force or weight.
Weight is also a measure of force.

10. From Newton’s 2nd Law, we can infer that…
As an object’s mass increases, it takes more force to change its acceleration.
Which would you rather play tennis with?
Which is easier to accelerate?

11. Forces are so common that we take many of them for granted.
Every push, pull, and any other movement is related to Newton’s Laws of Motion.
Understanding force is especially important to automobile manufactures.

12. Why is Force important?
An understanding of forces is also important in every sport…

13. Chapter 11: Forces
Section 2 – Gravity

14. What is gravity?
We have all seen video of astronauts walking on the moon.
As the astronauts try to move, they bounce across the surface. Why??
GRAVITY…or lack of gravity.
Definition: gravity – an attractive force that exists between all objects in the universe.
All objects with mass have gravity.

15. What is gravity?
From tiny grains of sand to the largest stars in the universe…
Everything that has mass has gravity.

16. What is gravity?
The force of gravity between two objects relies on two factors: mass and distance.
As the mass of an object increases, so does its gravity.
HOLY COW – TONS of Gravity
Lots of Gravity
More gravity
Some gravity

17. What is gravity?
The force of gravity between two objects relies on two factors: mass and distance.
As the distance between two objects increases, the force of gravity between them decreases.
The farther away from Earth you get, the less its gravity pulls on you.

18. Now, distance…
What happens to astronauts in the space shuttle when the get far away from Earth?
They float! This is also called being “weightless”.
Remember that the G-force decreases between two objects as the distance between them increases…
So, as you move far away from the Earth, it can no longer pull on you, and you can float!

19. The law of Universal Gravitation
The Law of Universal Gravitation explains the relationship between gravity, mass, and distance.
F = G [(m1 * m2) / d2)]
The equation shows that:
As mass increases, the force of gravity increases.
As the distance increases between two objects, the force of gravity between them decreases.

20. Effects of Gravity What happens when you drop something on Earth?
Its falls, of course. Lets put it scientifically.
On Earth, objects accelerate downward as they fall.
Gravity pulls all objects down
at the same rate.

21. Effects of Gravity Gravitational acceleration has the value
g = 9.8 m/s2 on Earth.
So, when you jump out of a plane on Earth, gravity will always pull you down at 9.8 m/s2.

22. After 1 second of falling, you’re moving…
About 10 m/s (9.8 m/s)
After 2 seconds of falling, you’re moving…
About 20 m/s (19.6 m/s)
After 3 seconds of falling, you’re moving…
About 30 m/s (29.4 m/s)
And so on…

23. More Effects of Gravity
Gravity affects your weight!
Because gravity is always pulling downward on you, it creates weight.
The stronger the gravity, the more weight you will have.
If a person weighs 150 lbs on Earth, she would only weigh 25 pounds on the Moon!!!
IMPORTANT: Weight is NOT the same as Mass!!

24. Section 3 – Newton’s 3rd Law
Chapter 11: Forces
Section 3 – Newton’s 3rd Law
Reaction Force
Action Force

25. Lets cut to the chase…what is Newton’s 3rd Law?
The 3rd Law of Motion
Lets cut to the chase…what is Newton’s 3rd Law?
Newton’s 3rd Law states:
For every action force, there is an equal and opposite reaction force.
In order for Newton's law to be true, there must always be more than one force present.

26. The 3rd Law of Motion
Forces come in pairs that act on different objects.
When you kick a soccer ball, you exert a force on the ball, and it does the same on your foot.
The soccer ball is exerting the same amount of force on the man’s foot. He can feel the ball exerting the force!

27. The 3rd Law of Motion
If forces are equal & opposite, why don’t they cancel out?
In a force pair, each force acts on a different object.
The force on one object may be enough to accelerate it…
But that same force may not be enough to accelerate the other object.

28. The reaction force is acting on the foot.
In the force pair below, the action force is acting on the soccer ball.
The reaction force is acting on the foot.
The forces don’t cancel because they aren’t acting on the same object!
6 N
6 N

29. Momentum
A small car and an 18-wheeler are traveling beside each other at the same speed.
If both vehicles brake at the same time with the same amount of brake force, which one will stop first?
The small car, of course. This is because it has less momentum.

30. (Mass x Velocity) Momentum
Definition: momentum – the amount of motion an object contains.
Momentum is measured by multiplying the mass of the object by the velocity or speed of the object.
(Mass x Velocity)

31. Momentum
An unbalanced force is needed to change the momentum off a moving object.

32. Momentum Conservation!
The Law of Conservation of Momentum states:
The momentum of a moving object is never destroyed – it is transferred.

33. Momentum Conservation
Momentum is transferred!
When a moving object hits another object…
The momentum of the moving object is transferred to the other object.

34. Momentum Conservation!

35. Bill Nye - Momentum