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Differential (mechanical device)
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<p>A differential is a <a href="/facts/Gear_train/znASyK8H">gear train</a> with three <a href="/facts/Drive_shaft/lHnhqzzT">drive shafts</a> that has the property that the <a href="/facts/Rotational_speed/DAVXQgXj">rotational speed</a> of one shaft is the average of the speeds of the others. A common use of differentials is in <a href="/facts/Motor_vehicle/AaXamA0w">motor vehicles</a>, to allow the wheels at each end of a <a href="/facts/Drive_axle/Eo5jWI3f">drive axle</a> to rotate at different speeds while cornering. Other uses include clocks and <a href="/facts/Analog_computer/3NhYoCML">analogue computers</a>. Differentials can also provide a gear ratio between the input and output shafts (called the "axle ratio" or "diff ratio"). For example, many differentials in motor vehicles provide a gearing reduction by having fewer teeth on the <a href="/facts/Pinion/CVbTozLS">pinion</a> than the <a href="/facts/Ring_gear/FMz8Fjg8">ring gear</a>. </p>