1. Friction
Ff =  . Fnorm
“” is the coefficient of friction…it represents the types of surfaces that are in contact with each other

2. Friction
Ff =  . Fnorm
 is a large value for rough surfaces (0.7 is a high )
 is a small value for smooth surfaces (0.3 is a low )

3. Friction
Ff =  . Fnorm
The coefficient of friction has two classifications:
Static – means stationary
Kinetic – means sliding

4. Friction
Ff =  . Fnorm
It takes a greater amount of force to start an object into motion than it does to keep it in motion. (sounds like an inertia application)

5. Friction Ff =  . Fnorm Fnorm ???
The “Normal Force” is a Supporting Force that is always perpendicular to the surface that the object rest on.

6. Ex. Horizontal Surface Suppose this crate has a mass of 2 kg. 2 kg
If the coefficient of static friction is 0.6, what is the minimum amount of force needed to start this object into motion? Fg
Fnorm
Solve for friction: Fnorm= Fg = m.g
Ff = µ.m.g = N
Ff = µ.m.g = 7.84 N
If the coefficient of KINETIC friction is 0.4, what is the amount of force needed to keep this object moving at a constant velocity?

7. Go to page 128 and complete # 17, 19
Be sure to include diagrams with force vectors labeled!
When done, check your answers in the back of the text book (odd practice problems have solutions in Appendix C)…p. 893