Work-energy theorem

Definition

Work-energy theorem in plain English

The work-energy theorem says the total work done on an object exactly equals the change in its motion energy — speed it up and you've added energy; slow it down and you've removed it. 'Work' here just means a force acting over a distance, written W = F × d × cos(θ), where the cos(θ) part accounts for whether the push lines up with the motion (a full push counts fully; a sideways push does nothing). So W_net = Δ KE means: add up all the pushing and dragging along the path, and that's how much the object's kinetic (moving) energy changed. Power, P = W/t = Fv, is just how FAST you deliver that energy — like the difference between carrying groceries upstairs slowly versus sprinting them up in half the time.

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