1. Friction, Gravity, and Elastic Forces Section 10.2 Page 380

2. Objectives for 10.2
Identify the two factors that will determine the friction force between two objects.
Identify the two factors that affect the gravitational force between two objects.
Be able to draw a force diagram of all forces acting on an object.
Explain why objects accelerate during free fall.
Explain when matter is considered to be elastic.

3. Friction
Friction: The force that one surface exerts on another when the two rub against each other.
Friction acts in the opposite direction of an object’s movement.
Friction opposes motion and can eventually cause an object to stop.
The strength of friction depends on:
1. The type of surfaces involved
2. How hard the surfaces push together

4. Sometimes FRICTION can be a positive thing …

5. Sometimes FRICTION can be a negative thing …

6. What are some instances when FRICTION is a positive thing?
What are some instances when FRICTION is a negative thing?

7. Types of Friction Static Friction
Friction that acts on objects to prevent them from moving

8. Types of Friction Sliding Friction
Friction that occurs when two surfaces slide over each other

9. Types of Friction Rolling Friction
Friction that occurs when an object rolls across a surface

10. Types of Friction Fluid Friction
Friction that occurs when a solid object moves through a fluid.
What is a fluid?

11. Any two objects anywhere in the universe attract each other
Gravity
Gravity … a force that pulls objects toward each other
Since it acts everywhere, this law is called the Law of Universal Gravitation:
Any two objects anywhere in the universe attract each other

12. Gravity The force of gravity between objects depends on:
The mass of the objects
The distance between the objects
The force of gravity between objects increases with greater mass and decreases with greater distance

13. Gravity

14. Mass vs. Weight Mass the amount of matter in an object.
A jar of nails has more mass than a jar of cotton balls.
The SI unit for mass is grams.
Weight – the amount of gravitational force exerted on an object
Weight = Mass X Acceleration due to gravity

15. Gravity and Motion
Free Fall --- When the force of gravity alone is acting on an object. (not considering any wind resistance)
What will fall fastest …an object of greater mass or lesser mass?

16. Gravity and Motion
Air Resistance --- A type of fluid friction caused by objects bumping into molecules in the air.

17. Gravity and Motion
Projectile Motion --- Motion from throwing an object with both a horizontal velocity and an acceleration vertically due to gravity

18. Gravity and Motion Projectile motion

19. Projectile Motion

20. Elastic Forces Matter is considered elastic, IF …
…it returns to its original shape after it is squeezed or stretched.

21. Compression
Compression is an elastic force that squeezes or pushes matter together

22. Tension
Tension is an elastic force that stretches or pulls matter

23. Compression and Tension: Elastic Forces
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