Keep Your Candy Cool With the Power of Evaporation!
Key Concepts
Water, heat, temperature, water cycle
IntroductionHave you ever wondered how sweating helps keep you cool on a hot summer day? Sweat, which is mostly water, cools us down when it evaporates. When water evaporates, it changes from a liquid to a gas. The gas carries away heat with it, helping to remove heat from your skin.Not only can evaporation cool down your body, it can also cool down other things, such as chocolate. Heat on a hot summer day can turn your solid candy bar into a gooey, melted mess, but how well can evaporation keep your chocolate from melting?
This activity is not appropriate for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.
BackgroundWhen water is heated enough, it turns into a gas. You see this when water is boiled. The gas phase of water is called water vapor, or steam, and it is hotter than liquid water. Consequently, as water evaporates, the vapor carries heat away from the water.Materials
Preparation
Procedure
Extra: You can repeat this procedure using thermometers to determine the starting temperature of each candy before putting them underneath the lamp, and the final temperature of each candy after it has been under the lamp for 10 minutes.
Extra: A gust of wind or a fan can feel very refreshing when you are sweating on a hot day. Is it refreshing for the chocolate candies as well? You can repeat this procedure to see how circulating air affects the candies by having a fan blow over them while they are under the lamp for 10 minutes—or fanning them yourself with a sturdy piece of paper. Does a fan affect how the candies melt? Does it affect their final temperatures?
Observations and ResultsWere you able to see the effect of evaporation on the chocolate candies? Did the candy wrapped in the wet paper towel show fewer signs of melting than the one wrapped in the dry towel?Just as sweating cools you on a hot day, when water is evaporated from the wet paper towel strip, it keeps the chocolate candy cooler compared with the candy wrapped in a dry towel. When the lightbulb heats the water on the wet strip, the liquid evaporates and turns into a gas, called water vapor. This vapor carries heat away, removing it from the area surrounding the candy, and keeps the candy cooler than it would be if there were no water to evaporate. This will probably not completely prevent the candy from melting but, overall, it should be visibly obvious that the candy in the wet paper towel strip melted less than the candy in the dry strip. If you tried fanning the chocolate candies while they were under the lamp, the breeze should have helped to increase the rate of evaporation. Because water vapor is less dense than dry air, it tends to stay around the object it evaporated from, making the surrounding air more and more humid and thereby difficult for additional evaporation to continue over time, because it has nowhere to go. The wind disperses the existing water vapor, making room for more water vapor to be made, which allows more evaporation—and thus cooling—to take place. Putting additional water on your skin or an object can also help increase the evaporation rate, which is why some people put wet bandanas around their necks when exercising. Cleanup
More to Explore"Digit's B-Day Surprise," CYBERCHASE from Thirteen/WNET, Educational Broadcasting Corporation, New YorkThe Water Cycle: Evaporation, from USGS "What's Sweat?" from KidsHealth "Keep Your Candy Cool with the Power of Evaporation!" from Science Buddies CreditsTeisha Rowland, PhD, Science Buddies
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Key Concepts
Water, heat, temperature, water cycle
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