Heat and Temperature
≈ 18 minTemperature tells you how hot or cold something is. It is measured with a thermometer, in degrees Celsius (°C).
Heat is different. Heat is energy on the move — energy transferred from a hotter object to a cooler one. An object does not "contain heat"; it contains thermal energy, and heat is the name for that energy crossing from one place to another.
The rule never varies: heat flows from hot to cold, and it keeps flowing until both objects reach the same temperature. Scientists call that state thermal equilibrium.
Worked example — a mug of rooibos. You pour tea at 82 °C and stand it on the table in a kitchen at 20 °C. Heat flows out of the tea and into the mug, the table and the air. After half an hour the tea reads 24 °C.
The drop in temperature is
And notice what does not happen: the tea never cools below room temperature. Once the tea and the room are at the same temperature, there is no longer a hot side and a cold side, so the flow stops.
Heat and temperature are not the same measurement. A 2 litre pot of water at 60 °C is cooler than a cup of water at 90 °C — but because there is so much more water in the pot, the pot holds far more thermal energy in total. Temperature answers "how hot?"; thermal energy answers "how much?".
A cold drink is taken out of the fridge and left on the table. After an hour it is no longer cold. What has happened?
What instrument is used to measure temperature?
A mug of rooibos tea is poured at 82 °C. Half an hour later a thermometer reads 24 °C. By how many degrees Celsius has the tea cooled?
A 2 litre pot of water is at 60 °C and a small cup of water is at 90 °C. Which statement is correct?