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Principle of the action of a couple

This animation shows the action of the couple. A couple is two equal and opposite forces that act on an object. In this case the two forces act on a rod and so rotate the rod. You will see that the magnitude of the torque (or moment of the couple) (Fd) changes as the distance between the two forces changes as the rod rotates.

© Keith Gibbs/John Bourne 2012