What process causes heat of friction to occur?

The process that causes heat of friction to occur is when two surfaces in contact move against each other. This interaction generates friction because of the microscopic irregularities and interlocking present between the surfaces. When the surfaces slide, they resist motion, and this resistance converts kinetic energy into thermal energy, resulting in an increase in temperature, or heat.

In this scenario, as the surfaces rub together, the energy expended in overcoming resistance manifests as heat of friction, which is why proper lubrication and maintenance are essential in mechanical systems to minimize overheating and wear.

The other scenarios do not contribute to frictional heating: when two surfaces move apart, there is no contact to create friction; if surfaces remain static, there is no movement to generate heat; and cooling down does not involve movement but rather a reduction in thermal energy. Therefore, understanding the dynamics of moving contact surfaces is critical for comprehending how heat of friction develops.