Question

During a marathon race, a runner is very hot. At the end of the race, evaporation and convection cool the runner.

a (i) Explain how evaporation helps the runner to lose energy. Use ideas about molecules in your answer.

(ii) Explain why hot air rises around the runner at the end of the race.
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Answer 1

Explanation:

i) Evaporation is a cooling process because when liquid turns to gas, it needs more energy, and so it has to take that energy from its surroundings. The energy is in the form of heat, and when the heat energy leaves with the evaporating liquid, the surroundings get cooler.

ii) Cool air is more dense than warm air, so the cool air 'falls through' the warm air. The shiny metal blanket which is use to wrap around the runner reflects the heat radiation from the runner back in, this stops the runner getting cold and hot arises around the Runner.