Types of Brakes
The Disc brake - a mechanical device used for slowing or stopping the rotation of a wheel. The brake disc, otherwise known as the "rotor", is made of cast iron in most cases, and is connected to the wheel or the axle. It looks like a metal circle.
To stop the wheel from turning, "friction" material, in this case the brake pads, which are mounted in a device called a brake caliper, is then forced, either mechanically, hydraulically or pneumatically, against both sides of the disc.
The friction created by the pad grabbing the discf then causes the disc and the attached wheel to slow down or to stop. Disc brakes have a much greater stopping performance than the older system of drum brakes, and are more reliable. This would be similar in principle to bicycle brakes, but with mechanical assistance added to the force of your foot on the brake pedal.
The Drum brake – this is a brake in which the friction is caused by a set of shoes or curved pads that will press against the inner surface of a rotating drum. The friction part of the brake, in this case called a "brake shoe" instead of a "brake pad", pushes out against the drums interior curve. The drum is connected to the rotating wheel. Drum brakes are sometimes still used in vehicles now days, but not often. The only reason they are still used is because of the weight and the cost advantages.