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

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 )

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

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)

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

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 = 11.76 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?

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