Final answer:
Friction between the brake pads and brake drum and other factors such as deformation of the tire and friction in the axle cause a brake drum to go concave.
Step-by-step explanation:
When a car applies brakes and comes to a stop, the process of converting kinetic energy into heat causes the brake pads and rotors to heat up.
The friction between the brake pads and the brake drum produces this heat. Additionally, the constant deformation of the tire and friction in the axle and bearings also contribute to the heating of the brakes.