Easy, Fun Science Activity: How to Make an Air Thermometer

Inventions: Where would society be without them? Galileo, one of the great masterminds of the 16th century, came up with an important invention: the air thermometer. What is an ‘air thermometer’? An air thermometer is an amount of air enclosed in by water in a tube. This article will teach you how to make an air thermometer, which will allow you to study the action of the trapped air when it is cooled or warmed.
You will need the following materials: a small container; a soda straw; a paper clip; an ice cube; water, and pencil and paper for notes.
Pour water into the container until it is 1/2 full. Put one end of the soda straw inside of the water. Make sure that it is resting on the bottom of the container. Water should rise up inside of the straw to the level of the container. Fold the top part of the straw. Secure it with the paper clip. This will enable some of the water to be trapped at the bottom of the straw, leaving an air pocket at the top of the straw. You have just created your very own air thermometer. Now for the experiment. Lift the straw straight up and out of the water. Keep it hanging over the container. Hold it just under the paper clip, and don’t squeeze the straw. Top of the straw should be air-tight. Ask yourself this question: Is water dripping out of the bottom of the straw? If yes, is it dripping fast or slow? Test: Check out water drop as it forms at the bottom of your air thermometer. Before the water drops, take your air thermometer and with the top part, touch the ice cube. The results will depend on how air tight your air thermometer is, so make sure it isn’t leaking. Take away the ice cube. Position the air thermometer by cupping your hand around it. Do not squeeze it! Ask yourself these questions: How will warming the air thermometer affect the trapped air? Will a drop of water start to form again? What result will occur regarding the trapped air after the warming? Note that if the trapped air begins to expand, it is most likely because of the heat from your hand. This is why water consistently drips, even when it is air tight. That same expanding air pushes the water out of the air thermometer. Grasp the air thermometer between two fingers of your left hand. Create heat within the trapped air of the air thermometer with your right hand. Right before the water drips, remove your right hand. Don’t force the drip, let it happen on it’s own. Note the condition of the drop as the water begins to cool. Ask yourself these questions: What will happen to the water drop as it cools? How does cooling affect the trapped air?
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Ramsey, William L., et al. Holt General Science. New York: Holt, Rinehart and Winston. 1979.

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