Sliding Friction Review

Sliding Friction Review

To visualize sliding friction, imagine a steel block lying on a steel table. Initially a force F (action) is applied horizontally in an attempt to move the block. If the applied force F is not high enough, the block will not move because the friction between the block and table resists movement. If the applied force is increased, eventually it will be sufficient to overcome the frictional resistance force f and the block will begin to move. At this precise instant, the applied force F is equal to the resisting friction force f and is referred to as the force of friction.

In mathematical terms, the relation between the normal load L (weight of the block) and the friction force f is given by the coefficient of friction denoted by the Greek symbol . Note that in the present context, normal has a different connotation than commonly used. When discussing friction problems, the normal load refers to a load that is perpendicular to the contacting surfaces. For the example used here, the normal load is equal to the weight of the block because the block is resting on a horizontal table. However, if the block were resting on an inclined plane or ramp, the normal load would not equal the weight of the block, but would depend on the angle of the ramp. Since the intent here is to provide a means of visualizing friction, the example has been simplified to avoid confusing readers not familiar with statics.