1. A Force that Opposes Motion http://www.youtube.com/watch?v=AX_lCOj LCTo Myth busters http://app.discoveryeducation.com/search? Ntt=friction Head Rush - MB

2. Friction  A force that opposes motion between two surfaces that are in contact.

3. The Source of Friction  Friction occurs because the surface of any object is rough.  The amount of friction depends on the force pushing the surfaces together and the roughness of the surfaces.

4. The effect of Forces on Friction  The greater the force (more weight), the greater the friction.  The less the force (less weight), the less the friction.

5. vs.

6. The Effect of Rougher Surfaces on Friction  Rougher surfaces have more hills and valleys that are in contact and stick to one another.

7. Types of Friction  Kinetic friction ○ Friction between moving surfaces; surfaces can slide or roll past one another.  Static Friction ○ Friction that occurs when a force is applied to an object, but the object does not move. Static frictions goes away as soon as the object starts moving.

8. Kinetic Friction Static Friction

9. Friction: Harmful and Helpful  Helpful: walking, bike riding, writing with pencil, brakes in a car  Harmful: wear down gears in a machine, skinned knee, soil erosion

10. Ways to reduce friction  Lubricants: motor oil, wax, grease  Ball Bearings  Smoothing down a surface

11. Ways to increase friction  Make surfaces rougher by scattering sand on an icy road