1. Friction and Gravity

2. 1. What is friction? The force that two surfaces exert on each other when they rub against each other.

3. Byproduct of friction…Heat!

4. 2. What direction does friction act? Acts in direction opposite to the objects in motion.

5. 3. How do you show friction as a force? An arrow opposite of the object’s motion Friction force Motion

6. 4. What determines the strength of friction? The types of surfaces (smooth or rough) and how hard the surfaces push together

7. 5. What are 4 types of friction? a. Static friction: acts on object NOT moving:

8. b. Sliding Friction Two solid surfaces slide over each other ex: pushing book across desk ex: once the sled is moving, sliding friction

9. c. Rolling Friction Object rolls across a surface ex: ball bearings

10. d. Fluid Friction Solid object moves through a fluid ex: oil, water, air (what do you use in your car to reduce friction?)

12. What are two ways in which friction can be useful? allows objects to remain in place! allows moving objects to stop to avoid colliding with other objects!

13. 6. What is gravity? The force that pulls objects toward each other

14. - Friction and Gravity Universal Gravitation Two factors affect the gravitational attraction between objects in the universe: mass and distance.

15. 7. How do you show gravity as a force on Earth? An arrow toward the center of Earth Gravity

16. 8. What is weight? The gravitational force exerted on an object http://youtube.com/watch?v=L55jImEhNZ0

17. 9. What is the acceleration due to Earth’s gravity? 9.8 m/s 2

18. What is your weight (on Earth)? Weight = Mass × 9.8 m/s 2 Weight = ?

19. 10. What is free fall? When the force of gravity alone causes an object to accelerate downward. Causes an object to accelerate downward at 9.8 m/s 2

20. 11. What is air resistance? Type of fluid friction as an object moves through air. Depends on speed and surface area

22. Air resistance

23. Free fall:

24. Gravity Air resistance Net Force accelerate downward Free fall:

25. Terminal velocity:

26. Gravity Air resistance 0 net force Move at constant speed Terminal velocity:

27. Gravity Air resistance Net Force

29. Gravity Fluid friction

31. Gravity Rolling friction Air resistance