Editing Differential (mechanical device) (section)

=== Purpose ===
[[File:Around the Corner (1937) 24fps selection.webm|thumb|1937 film about how differentials function]]

During cornering, the outer wheels of a vehicle must travel further than the inner wheels (since they are on a larger radius). This is easily accommodated when [[stub axle|the wheels are not connected]], however it becomes more difficult for the [[drive wheel]]s, since both wheels are connected to the engine (usually via a transmission). Some vehicles (for example [[go-kart]]s and [[tram]]s) use axles without a differential, thus relying on wheel slip when cornering. However, for improved cornering abilities, many vehicles use a differential, which allows the two wheels to rotate at different speeds.

The purpose of a differential is to transfer the engine's power to the wheels while still allowing the wheels to rotate at different speeds when required. An illustration of the operating principle for a ring-and-pinion differential is shown below.

{{gallery |mode=nolines |width=400 |align= left | File:Differential free.png |'''Differential operation while driving in a straight line:'''<br />Input torque is applied to the ring gear (purple), which rotates the carrier (purple) at the same speed. When the resistance from both wheels is the same, the planet gear (green) doesn't rotate on its axis (although the gear and its pin are orbiting due to being attached to the carrier). This causes the sun gears (red and yellow) to rotate at the same speed, resulting in the car's wheels also rotating at the same speed.

| File:Differential locked-2.png |'''Differential operation while turning left:'''<br />Input torque is applied to the ring gear (purple), which rotates the carrier (purple) at the same speed. The left sun gear (red) provides more resistance than the right sun gear (yellow), which causes the planet gear (green) to rotate anti-clockwise. This produces slower rotation in the left sun gear and faster rotation in the right sun gear, resulting in the car's right wheel turning faster (and thus travelling farther) than the left wheel.}}
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