Every number in a physics problem arrives wearing its units, and the units tell you what kind of thing it is before you do any math at all. A bare $\mathrm{m}$ is ground covered. A bare $\mathrm{s}$ is time passing. Put a slash between them — $\mathrm{m/s}$ — and you have a speed: distance per time. Stack a second time unit on — $\mathrm{m/s^2}$ — and the speed itself is changing every second: acceleration.

This lesson has no calculating in it. It is the skill underneath every other skill: read the sentence, find the numbers, and let the units point at what they are.

A teacher once put it best: a number without units is meaningless — unless, of course, it’s dimensionless. Everything in this room is built on that sentence.