Work
Work is done when a force causes a displacement. W = F·s·cos θ. Unit: joule (J). Zero work when force is perpendicular to displacement.
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Definition of work
Work is done when a force acts on an object and the object moves in the direction of the force (or has a component of displacement along the force). W = F·s = F s cos θ, where F is the force, s is the displacement, and θ is the angle between the force and the displacement. The SI unit of work is the joule (J): 1 J = 1 N·m.
When is work zero?
No work is done when the force is perpendicular to the displacement (cos 90° = 0). For example, carrying a bag horizontally does no work against gravity. Work can be positive (force and displacement in the same direction) or negative (e.g. friction opposing motion).
Why does holding a heavy box at rest not do work on the box?