Gainor

Meet Gainor, a cart who speeds up as work is done on him.

Work is done when a force moves an object through a distance. The work-energy theorem says that the net work done on an object, by all the forces acting on it, equals the change in its kinetic energy, W_net = ΔK.

Push a 10 kg cart from rest with a net force of 20 N over 5 m, on a smooth floor where friction can be ignored. The net work is 20 × 5 = 100 J, so the cart gains 100 J of kinetic energy. From ½mv² = 100 J, its final speed is √(2 × 100 / 10) ≈ 4.5 m/s.

If friction or another force pushes the other way, it does negative work and the gain in kinetic energy is smaller. When the net work is negative, the object slows down.

The theorem lets you find a final speed without tracking the motion moment by moment, and it is the starting point for the wider idea of conservation of energy.