1. Gravity
Chapter 3 Section 2

2. Effects of Gravity
Why does the apple fall down from the tree and not float around in space?
All objects have forces of attraction between them
this force of attraction is called gravity

3. Gravity is the force of attraction between objects and the Earth
the amount of gravitational force between objects depends on their masses and the distance between them

4. Weight
The force that is caused by gravity. The mass and the distance determine the weight.

5. Good test question
Do you weigh more, less or the same on the moon compared to Earth?

6. The Third Law of Motion
Chapter 3 Section 3

7. Newton’s Third Law Shooting a gun rowing a boat rocket propulsion
ice skater pushing off

8. Newton’s third law of motion
when one object exerts a force on a second object, the second one exerts a force on the first that is equal in size and opposite in direction
to every action force there is an opposite and equal reaction force

9. How is this law different from the other two?
Forces don’t cancel each other out even if they are equal and opposite.
There are always two objects involved
If forces are equal then how can a swimmer move through the water?
Newton’s second law determines the acceleration of an object

10. The forces are equal, but the masses may not be
the objects with less mass will accelerate more

11. Momentum
Why is it harder to stop a loaded train car verses an unloaded train car?
Why is it harder to stop a train car moving at 10 m/s verses a train car moving at 5 m/s?

12. Momentum is a property an object has due to its mass and velocity
can be calculated by multiplying mass times velocity
momentum = mass x velocity
r = m x v
units are kgm/s

13. Force & Changing Momentum
How do you stop the baseball from stinging your hand as you catch it?
Why to air bags work?
Newton’s 2nd law says F=ma
And So

14. Rearrange to have the equation
Ft=m(vf-vi) or Ft=mΔv
Where: Ft is called impulse
So the impulse equals the change in momemtum

15. Momentum has direction
momentum will change only if its mass or velocity changes
momentum can be transferred from one object to another
pool balls
car crashes
hockey players

16. Law of Conservation of Momentum
The total amount of momentum of a system does not change unless an outside force acts on the system
pool balls