2.  Friction is a resistive force caused by two surfaces sliding across each other.  Always acts opposite the direction of motion

3.  Static Friction - F s  Friction force between two stationary surfaces.  Kinetic Friction – F k  Friction force between two sliding surfaces.  F s is always greater than F k  Harder to start moving than to keep moving

4.  Coefficient of friction describes how rough the surface is. Higher is rougher.  Denoted by the Greek letter mu (μ)  pronounced “mew”  μ s = coefficient of static friction  μ k = coefficient of kinetic friction  μ is always positive, usually between 0 and 1.

5.  Regardless of type (static or kinetic)  To find static friction, use μ s  To find kinetic friction, use μ k