1. Friction  Friction results from relative motion between objects.  Frictional forces are forces that resist or oppose motion.

2. Coefficient of friction (  ) —Feet on rocks = large  —Polar bear on ice = small 

3. Friction (A Fun Formula) F f =  F n fun get it?

4. Friction (A Fun Formula) F f =  F n Normal force (N) Coefficient of friction No units! Friction force (N)

5. Friction F f =  F n  =  F f  F n F n = F f /  To solve for frictional force To solve for normal force To solve for coefficient of friction

6. Calculate force of friction  A box weighs 100 N (F n ).  As the box is pushed horizontally, the coefficient of sliding friction is 0.25.  Determine the force of friction resisting the motion.

7. To solve for frictional force: F f =  F n  F n = 100 N F f = (0.25)(100 N) F f = 25 N