Science from home: Evaporation and cooling


What you need:

  • Plastic bottle
  • Rag or wash cloth
  • warm/hot water
  • room temperature water
  • thermometer
  • Bowl/ container
  • clip
  • Paper
  • something to write with (pen, pencil, etc)


  1. Fill your bottle with room temperature water
  2. Cap the bottle and take the temperature of the water
  3. Write this number down so you can reference it later
  4. Soak your towel in the warm/hot water
  5. Wrap the towel around the bottle and use a clip to secure it
  6. Keep the thermometer in the bottle so you can reference temperature
  7. Check the temperature hourly and write down that temperature for the next 6 hours

The science and how this applies to our atmosphere:

At first, when you put the warm cloth on the bottle, you will notice the temperature increase. But over time, the temperature inside the bottle drops below where it started (at room temperature). This is because evaporation is a cooling process.

Inside the bottle, the temperature will initially jump a little because of the warmth around it. However, the warm rag eventually starts to dry out as the water in it evaporates (turns from liquid to gas). If you touch the rag, you’ll notice that it’s not only drier by the end of the experiment, but it’s much cooler.

What’s going on here is called evaporative cooling, or the cooling of air due to latent heat absorption of water molecules. More energy is required for water to turn from a a liquid to a gas. As a result, heat is absorbed and colder temperatures are produced.

On a larger scale, we see this happen to our outside temperature after it rains. As the puddles and rain drops start to evaporate, or dry up, we’re surrounded by evaporative cooling, which lowers the temperature.

Other ways you see this every day:

On a hot day, you might notice that you sweat and have probably been told that’s your body’s natural way to cool off.

It’s actually not the sweat droplets that cools you off, but the evaporation of that sweat. Just like evaporating the water from the washcloth in the experiment lowered the temperature of the water, and like rain can lower the outside temperature, those beads of sweat help to cool us on on a hot summer day!

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