2. Braking problems

2.1 Problem definition

To bring a moving body back to rest, we have to absorb the mechanical energy it has stored and transform it into heat by friction in the brake.

Friction work is due to :

• the action of gravity on the mass being manoeuvred, which produces a torque, called the torque of gravity; this torque acts positively on descent and negatively on ascent. Transmission efficiency reduces the effect of the torque of gravity on descent, and increases it on ascent;

• the action of passive resistances, resulting from friction at various points, which give a passive resistance torque; this torque always assists the braking torque (for road vehicles, it is introduced by rolling resistance,...