1. Force of friction depends on the surfaces in contact and the Normal Force between them

2.  Ff = μ Fn  Ff = force of friction, Fn = normal force  μ = coefficent of friction which is a property of the materials involved.  μ is a number without units and is typically has a value between 0.1 and 1.

3.  Values for the coefficient of friction, μ Coefficient of frictionMaterials in contact 0.8Rubber on concrete 0.2Wood on wood 0.1Ice on ice

4.  Use the Frictional Force equation whenever there is a force = mass x accel problem (F = ma_) involving friction

5.  Solving problems with friction  Draw force diagram  Write Fnet = ma for both x- and y- axis  Solve

6.  Block of wood pulled across table  Mass = 5kg, Fpull = 60N, μ = 0.4  Find acceleration of block