Work: the energy a force transfers when it moves something

Holding a heavy box still feels like hard work, but in physics you have done no work on it: you have not moved it.

In physics, work is energy transferred by a force when the force moves its point of application — the place where the force acts.

Push a trolley along a corridor and you have done work on it: the push moved with the trolley, and energy has been transferred to it.

• $F$ is the force doing the work, in newtons (N).
• $s$ is how far the object moves while that force acts, in metres (m) — measured along the force, not sideways.
• $W$ is the energy transferred, in joules (J).

Work is a way of counting energy: do $120\ \text{J}$ of work on a trolley and you have transferred $120\ \text{J}$ of energy to it.

The unit $1\ \text{N m}$ is given its own name, $1\ \text{J}$, because work is an energy transfer.