Work Done by a Torque or Couple - QS Study
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Suppose two equal and opposite forces F act tangentially to a wheel W, and rotate it through an angle θ (Figure).

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Then, the work done by each force = Force x distance = F x r

(since r θ is the distance moved by a point on the rim)

Total work done W = F r θ +F r θ = 2 Fr θ

but torque τ = F x 2r = 2 F r

so, work done by the couple, W = τθ

 

Examples of couple are

  1. Forces applied to the handle of a screw press,
  2. Opening or closing a water tap.
  3. Turning the cap of a pen.
  4. Steering a car.