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In physics, a pair of equal parallel forces that are opposite in direction. Couples produce or prevent the turning of a body. The forces used to turn the steering wheel of a car constitute a couple; each hand exerts a force, parallel but opposite in direction, yet they work together to achieve the same goal. A couple is also used to turn a screwdriver or a doorknob, and the pair of forces acting on the opposite poles of a compass needle as it points somewhere between north and south are a couple.
This entry comes from Encyclopædia Britannica Concise. For the full entry on couple, visit Britannica.com.