Nicholas Academy

Science | Science Experiment of the Week 6 | 264 - A Cool Experiment

Evaporation, Air Humidity, Bathtub - Why you feel cool when you get out of the tub.

This Week's Experiment - #264 A Cool Experiment

These experiments are from Robert Krampf - The Happy Scientist

This week's experiment comes from a book I am writing on Household Science. At least, that is the working title for now. I have been researching the chapter on Science in the Bathtub, which means spending hours in the tub trying out different things. One of the things that I wanted to explore was why you always feel cool or cold when you get out of the tub. To try this, you will need:

some warm water
a washcloth or paper towel

Actually, there is more than one reason that you could feel chilled when you get out of the tub. If the water was very warm, then the air will feel cooler by comparison, but even if the water was cool and the air was warm, you could still feel a chill. To see why, dip the washcloth into some warm water. Squeeze out the excess and place the washcloth on your face. It should feel nice and warm.

To cool the cloth, hold it by one edge and swing it back and forth a few times. Then place it back on your face. You should notice that it is now quite cool.

Why would waving the cloth in the air make it cooler? This will work even if the air in the room is quite hot, so the air itself is not cooling the cloth. Instead, it is being cooled by evaporation. When liquids evaporate, they soak up quite a bit of heat. As you swing the wet cloth through the air, some of the water evaporates. This removes quite a bit of heat from the cloth, leaving it nice and cool.

This is the idea behind sweating. When you get hot, you sweat. The sweat evaporates and cools your skin. It is also the principle used in the mist cooling systems that are becoming popular. They spray a very fine mist of water into the air. The water evaporates and cools the air, making you more comfortable on a hot day.

One way to cut down on the post-bath chill is to keep the bathroom nice and steamy until you are dry. If the air is already very humid then the water will not evaporate from your skin and you stay warmer.

I am almost finished with the bathtub chapter. Next comes Science in Your Closet. I am not sure if spending hours in a dark closet will be as much fun, but at least it will give Lisa something new to laugh about.

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