1. Friction

2. A World Without Friction…

3. Friction A force that resists motion Occurs due to the attraction between particles

4. Two Types of Friction Kinetic Friction Occurs when the object is in motion Resists movement

5. Two Types of Friction Static Friction Occurs when the object is stationary Resists being put in motion

6. How do we measure friction? Weigh an object with a force scale Pull an object with a force scale Divide the two values We call the result the coefficient of friction

7. Coefficient of Friction (  ) Ratio of the magnitude of the frictional force to the normal force (how much force is pushing up from the surface) Coefficients of friction can be found in the text – Page Depends on the two surfaces in contact

8. http://www.engineeringtoolbox.com/friction- coefficients-d_778.htmlhttp://www.engineeringtoolbox.com/friction- coefficients-d_778.html Pick one!

9. The Math  - Coefficient of Friction (no units) F fr – Force of Friction (N) F N – Normal Force (N)

10. Example # 1 The coefficient of static friction between ___ and ___ is _____. Find the minimum force required to start an 8.0 kg mass moving.

11. Example # 2 An 8.0kg teflon pot is on a steel table. If it takes 9.4N of force to keep the pot moving at a constant speed. What is the coefficient of friction between the pot and table?

12. Controlling Friction How can we reduce friction? Why do we need to reduce friction?

13. Controlling Friction What is used to increase friction? Why do we need to increase friction?

14. Industrial Applications Inertial Friction Welding ▫Video Creating a Friction Fire http://www.youtube.com/watch?v=VOmwLxgI06c