Assumptions - Static and Kinetic Friction

The applet simulates a block on a horizontal surface with friction. Both static and kinetic friction are simulated. An applied force is acting on the block.

1. The simulation assumes the simple model for the friction force that is adopted in all general physics texts. The model assumes that the magnitude of the friction force is proportional to the magnitude of the normal force and that the coefficient of kinetic friction is independent of the velocity.

Specifically, the following equations are used in the simulation.

The maximum value Fstat,max of the magnitude of the static friction force is given by

Fstat,max = μs N space(1)

where μs is the static coefficient of friction and N is the magnitude of the normal force.

The magnitude Fkin of the kinetic friction force is given by

Fkin = μk N space(2)

where μk is the kinetic coefficient of friction.

2. In this applet, μk and μs are related so that μk is in the range

0.5μs less or equal μk less or equal 0.9μs.space(3)

This is a somewhat arbitrary assumption, which applies to many, but not all real situations. In general, kinetic friction is less than static friction, and this assumption reflects this fact.

3. The surface (table) the block is moving on is horizontal.