Each vehicle of an air braked train will have a cylinder with pressurized air on both the `train pipe' and `reservoir' sides of the piston while the brakes are off. The brakes are applied by releasing the pressure in the train pipe side, the resulting pressure differential will put the brakes on. The pressure is originally supplied from the locomotive via the train pipe and a one-way valve ensures that the reservoirs on each vehicle are pressurized. The train pipe runs the length of the train thus providing a fail-safe system should the train part.
A predominantly flat surface which when introduced into the airflow disturbs an otherwise smooth airflow and creates a large amount of drag thereby slowing the airframe.
Heavy trucks use air brakes exclusively to stop the rig. When the brakes are applied, air enters the brake chamber. The air forces a push rod out, turning a slack adjuster that rotates an "S" cam. This in turn forces the brake shoes against the drum, applying the friction required to slow down or stop the truck.