Abstract

Objective

Introduction

Click here to watch a video clip from "Digit's B-Day Surprise," the CYBERCHASE episode that inspired this science fair project idea. Presented by pbskidsgo.org.

You've probably noticed that when you're outside on a hot summer day, your body starts to sweat. But did you know that sweat, or perspiration, is actually your body's way of cooling down? Sweat, which is mostly water, cools us down when it evaporates.

Evaporation is the process that occurs when water changes from a liquid into a gas (in this case, the gas is water vapor). When your sweat evaporates, it carries heat energy from your body with it. The faster your sweat evaporates, the more heat is carried away, and the more the skin surface from which it evaporates is cooled.

As water evaporates from an object, it makes the air above the object more humid, (filled with more water vapor) which, in turn, slows down the evaporation process. This is because once the air is already full of water vapor, there is nowhere for the water on your skin to evaporate. But if you fan the moist, humid air away, then the water can evaporate more quickly. That's why you feel cooler if you fan yourself or if there's a gust of wind.

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. These misters help out your body's natural sweat cooling system by providing more water to evaporate and carry away heat energy from your body. Another way that you can keep cool on a hot day is by dipping a bandana in water and wearing it around your neck. The extra water from the bandana causes more evaporation, which keeps your body even cooler than it would be with only sweat.

You can apply the same process of evaporative cooling that your body uses in order to cool down objects. In the CYBERCHASE episode, "Digit's B-Day Surprise," the CyberSquad must use evaporative cooling to keep Digit's chocolate sculpture birthday present from melting while traveling through the desert. Click on the video box above to watch the CyberSquad use the power of evaporative cooling to save Digit's birthday present.

You can also watch this video clip from CYBERCHASE For Real to see how Harry uses evaporative cooling to cool down on the tennis court: http://pbskids.org/cyberchase/forreal/for_real_hi.html?episode=601

How can you use evaporative cooling to keep chocolate candies from melting? This science fair project will help you find out!

Terms, Concepts, and Questions to Start Background Research

• Perspiration
• Evaporation
• Gas
• Water vapor
• Humidity
• Evaporative cooling

Questions

• How does sweat cool your body down?
• What are some ways people use evaporation to keep cool?
• How do engineers use evaporation to keep objects cool?

Bibliography

This science fair project is based on the following episode from CYBERCHASE on PBS KIDS GO!:

• Thirteen/WNET New York. (2008). CYBERCHASE: Episode 601: Digit's B-Day Surprise. Educational Broadcasting Corporation, New York. Retrieved February 13, 2009, from http://pbskids.org/cyberchase/parentsteachers/show/episodes/601.html

Check out this website to learn more about evaporation and the water cycle:

• USGS. (2008). The Water Cycle: Evaporation. Retrieved February 13, 2009, from http://ga.water.usgs.gov/edu/watercycleevaporation.html

Learn more about sweat from this website:

• Gavin, Mary L. (2006, May). What's sweat? Retrieved February 13, 2009, from http://kidshealth.org/kid/talk/yucky/sweat.html

This website offers help with creating graphs:

• National Center for Education Statistics. (n.d.). Create a Graph. Retrieved February 22, 2009, from http://nces.ed.gov/nceskids/CreateAGraph/default.aspx

Materials and Equipment

• Paper towel (3 sheets)
• Scissors
• Small bowl of room-temperature water
• Chocolate-covered peppermint candies in foil wrappers (6)
• Ruler
• Desk lamp with adjustable height and 60-watt (W) lightbulb. Note: If you don't have an adjustable-height lamp, a normal desk lamp and a pile of books can be used instead.
• Timer
• Lab notebook

Experimental Procedure

1. Cut your paper towel sheet into strips that are about 1 1/2 inches wide.
2. Take one paper towel strip and wet it by dipping it into the bowl of water and carefully wringing it out.
3. Keeping the candies in their foil wrappers, wrap one of the candies in the wet paper towel strip and wrap another candy in a dry paper towel strip.
4. Place the two candies side-by-side beneath the lamp. Bend the lamp down until the lightbulb is 1–2 inches away from the candy.
   1. If you don't have an adjustable-height lamp, prop the candies up on a pile of books until they are within 1–2 inches of a 60-W lightbulb in a normal desk lamp.
5. Using your timer, time the candies for 10 minutes.
6. After 10 minutes, take the candies out from beneath the lamp. Remove the paper towel strips and open the foil wrappers.
7. In your lab notebook, record your observations about what happened to the candy wrapped in the wet paper towel versus the candy wrapped in the dry paper towel.
8. Repeat steps 1–7 two more times with new candies and paper towel strips. Are your observations consistent between trials? Can you use the information you learned from the Introduction and your background reading to explain your observations?
9. To gain an even deeper understanding of evaporative cooling, try the Variations below.

Variations

• Try the experiment again, using thermometers to determine the starting temperature, and the final temperature that each candy reaches after 10 minutes beneath the lamp. Graph your results. Note: for help creating graphs, try the Create a Graph website.
• What happens if you use a paper fan to fan the paper towel-wrapped candies while they are underneath the lamp? How does this affect the melting of the candies? What about the final temperature of the candies?

• For more science project ideas in this area of science, see Chemistry Project Ideas.

Credits

Kelsey Woods, Cyberchase Intern

Edited by Sandra Slutz, PhD, Science Buddies

The inspiration for this science fair project is the episode "Digit's B-Day Surprise" from CYBERCHASE on PBS KIDS GO!:

• Thirteen/WNET New York. (2008). CYBERCHASE: Episode 601: Digit's B-Day Surprise. Educational Broadcasting Corporation, New York. Retrieved February 13, 2009, from http://pbskids.org/cyberchase/parentsteachers/show/episodes/601.html

Watch CYBERCHASE on PBS KIDS GO! Check local listings or visit www.pbskidsgo.org/cyberchase. CYBERCHASE is produced by THIRTEEN in association with WNET. All rights reserved. CYBERCHASE is a trademark of THIRTEEN. The PBS KIDS GO! logo is a registered mark of PBS and is used with permission.

Last edit date: 2011-10-24 23:39:00