1. Chapter 10 Section 2
Friction

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

3. The Causes of Friction
The strength of the force of friction depends upon:
how hard the surfaces push together and the type of surfaces involved.
(Smooth surfaces produce less friction)

4. Smooth surfaces produce less friction
Greater force produces more friction

5. Types of Friction Static:
The friction that acts on objects that are not moving

6. Must use extra force to start the motion of stationary objects

7. Once object starts to move, there is no static friction

8. Sliding
Occurs when two solid surfaces slide over each other.

9. Can be useful, Sand on ice to gain traction, brakes

10. Can be harmful: Fall off bike and skin knee, heat produced

11. Rolling
When an object rolls across a surface
Easy to overcome

12. Example Ball bearings help reduce the friction between the wheels and the rest of the unit

13. Fluid Friction Occurs when a solid object moves through a fluid
Easy to overcome

14. Fluids are used between 2 solid moving parts, the solids move through the fluid, not against each other

15. Occurs between you and the air when you ride a bike

16. Gravity Gravity is a force that pulls objects toward each other.
Gravity is everywhere in the universe

17. Law of Universal Gravitation: the force of gravity acts between all objects in the universe

18. Factors that affecting Gravity
Mass: The amount of matter in an object
The more mass an object has, the greater its gravity

19. The Distance between the objects
The greater the distance between the objects, the less gravitational force between them

20. Weight and Mass
Is the measure of the amount of gravitational force exerted on an object

21. Weight varies with the gravitational pull, mass does not