Investigating what makes water evaporate fastest
Chemistry · Key Stage 2 · The School
Three things that might matter
Heat, surface area and moving air can all change how fast water evaporates. To find out which matters most, you must test one thing at a time. Change two things together and you cannot say which one caused the difference.
Planning the surface-area test
Pour the same amount of water into a narrow cup and a wide, shallow tray. Put both in the same room, at the same temperature, with no draught. Measure the water level, or weigh each container, once every hour. Everything is the same except the shape of the container.
Reading the results
The wide, shallow tray usually empties fastest. More of its water is exposed to the air at once, so more particles can escape at the same time. The narrow cup has far less surface touching the air, so it evaporates more slowly, even though it holds the same amount of water.
Doing it for real
Pour 100 ml of water into a saucer and 100 ml into a mug. Leave both on the same windowsill overnight. In the morning, the saucer is nearly dry and the mug has barely changed. Same water, same room, same time — the only difference was surface area, and the result shows it plainly.