The Effect Surface Temperature Has on Kinetic Friction

Friction is a common force that significantly affects the motion of nearly every moving object we see in everyday life. It is routinely studied and used in the analysis of motion in all levels of high school and college physics classes. In particular, static and kinetic frictions are two types of friction that are defined in commonly used textbooks as: where $fs,k$ is either the static or kinetic friction force, respectively, $μs,k$ is the coefficient of static/kinetic friction, and $FN$ is the normal force. Students are therefore taught that the only quantities that affect static and kinetic friction are the nature of the two materials that are in contact with each other and the force at which the two surfaces press against one another. In this paper we describe a relatively simple experiment that can be done to test the effect surface temperature has on kinetic friction, and that depending on the materials being used, the coefficient of kinetic friction does indeed increase as the surface temperature of one of the materials increases. Because such effects are not normally discussed in standard introductory physics textbooks, this experiment could be used as a nice inquiry activity in introductory physics courses.