INCREASING TRACK FRICTION
The difference between sliding and rolling friction is well illustrated in a locomotive. The driving wheels are turned around by steam power. They must either roll or slide on the track and the load they will pull without slipping is a measure of the excess of sliding friction over rolling friction. To increase the traction or the adhesion of the locomotive to the track it is provided with a number of driving wheels. In some of our largest locomotives driving wheels are placed under the tender so as to obtain a maximum of traction.