Work (W = Fd cos θ)

Also known as W = Fd · work done by a force

W=FdcosθW = F d \cos\theta

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In physics, work is force applied through a distance — and only the component of force along the motion counts, which is where the cos θ comes from. Pull a sled with 100 N on a rope angled 30° above the snow for 20 m, and you do W = 100 × 20 × cos 30° ≈ 1732 J, not the full 2000 J. The term itself was coined by the French engineer Gaspard-Gustave de Coriolis in 1826, precisely to compare what steam engines and horses could deliver.

Two useful edge cases: a force perpendicular to the motion (θ = 90°) does no work at all — the Moon's orbit costs gravity nothing — and a force opposing the motion, like friction, does negative work, showing up as cos θ below zero. Solving for θ uses the arccos principal branch, 0° to 180°, which conveniently covers the entire physical range of angles between two directions.

Work (W = Fd cos θ)
W=FdcosθW = F d \cos\theta
Where
  • WW= Work
  • FF= Force
  • dd= Displacement
  • θ\theta= Angle between force and motion