Dip a spoon in your hot chocolate and dip a spoon in a hot bath. The hot chocolate is hotter — but the bath could melt a whole snowman, and the mug could not. Those are two different questions. Temperature is where the thermometer sits — a reading, in °C. Heat is energy on the move, and it is counted in joules — the same joules food labels count. Degrees describe; joules flow.

This chapter runs on four characters, so meet them properly. $Q$ is the heat — joules (or kilojoules, kJ, a thousand at a time). $m$ is the mass being warmed, in kilograms. $\Delta T$ is the temperature change — $\Delta$ is the Greek letter delta, and $\Delta T$ is said delta-T: final reading minus starting reading, the little word by wearing a symbol. And $c$ is the specific heat capacity — each material's price tag for warming up, which the next lesson puts to work in $Q = mc\,\Delta T$ (read aloud: Q equals m c delta-T). For now, the game is just telling the four apart — and their units do it for you.