Melting, boiling and evaporation · 3 parts · syllabus 2.2.3

Why does sweating cool you down?

Wrap two tubes of hot water in paper towels, wet one towel and weigh it as the water evaporates, while a magnifier shows the fastest particles escaping from its surface. Then test how a fan, a smaller surface and a cooler start change the rate of evaporation, and compare evaporation with boiling.

Start learning Explore the experiment

A runner in an orange vest stands with one hand on a hip at the edge of a running track, resting after a run, beside a bench with a water bottle.

Follow the idea

Melting and boiling
Melting and boiling at fixed temperatures; melting and boiling points of water; heating and cooling curves, and condensation and solidification
Not started
Evaporation and cooling
Evaporation: the more energetic particles escape from the surface, so the liquid left cools; how an object in contact with an evaporating liquid cools
Not started
What changes the rate of evaporation
What changes the rate of evaporation: temperature, surface area and moving air; how evaporation differs from boiling
Not started

Two boiling tubes of water on two balances, each closed by a cork with a thermometer through it. The lower half of each tube is wrapped in a paper towel: the left towel is dry, the right one wet. A dropper stands in a small beaker of water in front.

The experiment · Weigh a wet towel · what speeds evaporation

Run it yourself, or project it for the class

Use the apparatus step by step and look closely at what happens. The whole experiment fits one screen, so it works on a projector too.

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Final check

Explain it on your own across all three parts. Hints and keys stay closed until you submit.

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Return and recall

Come back after one to two weeks and answer with the lesson closed.

Recall questions

For teachers

Printable worksheets with their answer keys, the final check and the return questions for this module.

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Scope and sources

Cambridge IGCSE Physics 0625 · 2026–2028 v2 · Original learning materials.

Melting and boiling, with the melting and boiling points of water at standard atmospheric pressure (2.2.3.1, 2.2.3.2); condensation and solidification in terms of particles (2.2.3.3); evaporation as the escape of more energetic particles from the surface of a liquid (2.2.3.4); how evaporation causes cooling of a liquid (2.2.3.5); the differences between boiling and evaporation (2.2.3.6); how temperature, surface area and air movement over a surface affect evaporation (2.2.3.7); how the cooling of an object in contact with an evaporating liquid happens (2.2.3.8). Specific heat capacity is in SHC01; conduction, convection and radiation are in TRANS01.

Apparatus, amounts and times in the experiment are illustrative. Real practical work follows a teacher-approved safety method.

Official Cambridge syllabus

Why does sweating cool you down?

Follow the idea

Melting and boiling

Evaporation and cooling

What changes the rate of evaporation

Run it yourself, or project it for the class