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Cool It!

Experiment with evaporation to keep an object cool on a hot day.

Goal: To recognize that the evaporation of water can be used to cool something.

Time: 30 minutes to an hour

Space: Desk or table


  • timer
  • 2 chocolate-covered peppermint candies in foil wrappers
  • desk lamp with adjustable height and 60 Watt bulb
  • water
  • paper towels, 5-10 sheets
  • Optional Material: 2 thermometers


  • Before starting, tear paper towel sheets into strips about 1 ½” wide. Set up a work space for your child that includes:
  • desk lamp
  • bowl of water (at room temperature)
  • 2 paper towel strips
  • 2 chocolate-covered peppermint candies in foil wrappers
  • Optional: Include paper for your child to make a paper fan and 2 thermometers.
  • Optional:  Preview the episode or clip, and if using them with your child, cue up the videos via the links above.


  1. Ask your child to share her favorite ways to cool down on a hot day (go swimming, go under a sprinkler, etc.).
  2. Invite her to dip one fingertip into some water that is at room temperature, then hold it up with the rest of the fingers on one hand. Ask: How does the wet fingertip feel compared with your other fingertips? (Cooler.) Say: Now wave the wet fingertip. How does that feel? (Even cooler.)
  3. Explain that our bodies have built-in coolers! Our sweat cools our bodies as the water in it evaporates from our skin.
  4. Optional: Use the episode or clip to further explore this idea.
  5. Ask: Do you think we can use the evaporation of water to keep a chocolate-covered patty cool so it doesn’t melt? Begin the experiment to find out.
  6. Review how your child will do the experiment. Keeping the peppermint patties in their foil wrappers, she should wrap one in a dry paper towel and the other in a wet paper towel. (To wet it, dip it into the water and wring it out.) Next, she should place the candies side-by-side under the lamp, and bend the lamp down until the bulb is 1-2 inches from the candy. Using the timer, she will time her patties for ten minutes and then check to see what happened.
  7. Optional: Have your child wrap the bulb end of a thermometer against each patty using the dry and wet paper towels. Note the temperature on each before placing under the lamp.
  8. After ten minutes, have your child remove the paper towels, open the wrappers, and compare what happened to the candies under the different conditions (wet vs. dry). If using thermometers, have her also note the temperatures on both thermometers after ten minutes.
  9. Discuss what your child observed. Ask: How did the candies compare when you opened them? (The dry one was more melted than the wet one.) If she used thermometers, ask her to describe the difference in the temperature at the end of the experiment.
  10. Ask your child if she can now think of new ways to cool down on a hot day. (For example, wrap a wet cloth around the neck or forehead!)

Take It Further

Share this activity’s Science, Technology, Engineering, Math (STEM) connections and invite your child’s comments:

In places with hot weather, engineers design misters—machines that spray a fine water mist—for use in public places to help people keep cool.

Talk About It

Ask: What did you learn today that you didn’t know before?

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Produced by: Funding is provided by:
WNET logo
Additional funding is provided by Lynne and Marc Benioff, the Tiger Baron Foundation, Shailaja and Umesh Nagarkatte and Ellen Marcus.
The JPB Foundation NSF Heising-Simons Foundation EY

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