Friction and frictional heat generation

This normal force leads to a friction force $F_f$ which equals

$$F_f = \nu \: F_n$$

where $\nu$ is the friction coefficient (see contact_friction. The friction force causes heat generation rate $Q$:

$$Q = \eta \: F_f \: v_f$$

where $v_f$ is the slip velocity, and the factor $\eta$ is a user specified factor which determines which part of the frictional energy loss is transformed into heat ($\eta$ is between 0 and 1; see contact_heatgeneration).