Friction Forces AP Physics C Mrs. Coyle

Outline Static Friction Kinetic Friction Coefficient of Friction (Static and Kinetic)

Friction: the resistance to an object’s motion when it travels against a surface or in a viscous medium. It has a direction parallel and opposite the direction of motion. Static Friction, fs : the frictional force that exists when a force is applied to attempt to move an object across a surface but the object is not yet set in motion; fs counteracts the applied force. Kinetic Friction, fk : the frictional force that exists when an object has been set in motion across a surface.

Active Figure- Static and Kinetic Friction http://www.csupomona.edu/~skboddeker/132/notes/Active%20Figures%20Media/AF_0516.swf

Coefficient of Friction, µ fs ≤ µs N (the equality holds in the case of impending motion). fk= µk N Values of µ depend on the surfaces and are usually between 0.03 and 1.0 µ has no units

Active Figure-Incline Plane With and Without Friction http://www.csupomona.edu/~skboddeker/132/notes/Active%20Figures%20Media/AF_0519.swf

Example 1: Find the coefficient of friction as a function of the angle ɵ, for the inclined plane shown a) for the case where the object is moving at constant velocity b)where the object is moving at a constant acceleration. ɵ m

Example 2: A 1.00kg book is held against a wall by pressing it against the wall with a force of 50.00N. What must be the minimum coefficient of friction between the book and the wall, such that the book does not slide down the wall? F