Application of Friction
Brakes
Friction can be used to use up energy.
Brakes are a great example of how friction can be useful.
There are several types of brakes including:
Drum brakes
A drum brake usually consists of two brake shoes (pads) installed inside a rotating cylinder (Drum). To brake, the shoes are forced apart so that they make contact with the inside surface of the drum. The subsequent friction converts the kinetic energy of the rotating drum into heat, slowing it down.
Disc brakes
A disc brake is used to stop a disc that is attached to a rotating shaft.
Callipers are attached to a frame that is stationary relative to the moving shaft. An actuator causes the callipers to squeeze pads against the metal disc. This converts the driving force into heat making the disc, and whatever it is attached to, slow down.
A disc sometimes has holes in it. When the pads press hard up against the disc a lot of friction is produced, generating heat. This heat causes a plasma (hot gas) to form between the pad and the disc allowing the disc to slip, reducing its efficiency. The holes are intended to allow the plasma to escape so that, when braking, the pad makes contact with the disc at all times.
Power transmission
Friction can be used to transmit power from an engine in a controlled way.
A clutch is a device that is used to connect or disconnect the driving force from the wheels. It is used when the a vehicle is stopped or when it is neccessary to change gears.
Pressure is applied to hold two plates together. The touching surfaces of the plates are rough to ensure a good grip.
As one plate is moved away from the other, the pressure is reduced allowing the two plates to slip across each other, lowering the amount of force trasmitted to the driven shaft, slowing it down. Eventually, when the driven plate is held away from the driving plate, the speed of the driven shaft becomes zero.
Press the pedal to disengage the clutch plates.
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