Every quantity in this chapter is priced in one currency: the joule. $1\ \mathrm{J} = 1\ \mathrm{N \cdot m}$ — one newton pushed through one metre. Unpack the newton and it is $\mathrm{kg \cdot m^2/s^2}$, but N·m is the form to carry: a force, times the distance it acts through.

Two machines open the account. $W = Fd$ (read aloud: W equals F d) prices work — energy spent pushing — where $W$ is the work in joules, $F$ the force in newtons, and $d$ the distance it acts through, in metres. $E_k = \tfrac{1}{2}mv^2$ (E-k equals one-half m v-squared — the subscript k is said “k”, for kinetic) prices motion, with $E_k$ the kinetic energy in joules, $m$ the mass in kilograms and $v$ the speed in m/s. Watch the units in every scenario: a bare N is a force waiting to act, a J is energy banked, and a W — a watt, one joule per second — is energy on the move.

Yes, the letter W does double duty this chapter: symbol for work, unit of power. The exam knows. Read carefully.