Friction is the name given to the force which opposes the relative sliding motion of two surfaces in contact with one another lIt plays a notable part in our daily lives. For example, we are reminded of the importance of friction every time we slip up on
an icy pavement or a polished floor. Walking would be impossible if there were no friction between the ground and the soles of our shoes. If the pavements were perfectly friction less, then one way we could get about would be with the aid of pegs in the soles of our shoes and holes in the pavements to correspond. Otherwise, some simple form of rocket or jet propulsion might be used (Chapter 4) but this is left to the reader’s own imagination. Quite often our lives depend on the force of friction in the
brakes of an automobile or a railway train. There are one or two technical terms used in the study of friction which we hall
illustrate with a few simple experiments.