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Science Fun:
How to Make a Homemade Thermometer

This project is really interesting and fun; however, it does need close adult supervision to complete it. This is a really fun addition to a homemade weather station!

Project Supplies:

Tap water
Rubbing alcohol (do not drink this)
Clear, narrow-necked plastic bottle (11-ounce water bottles work well)
Food coloring
Clear plastic drinking straw
Modeling clay

Project Directions:

1. Pour equal parts of tap water and rubbing alcohol into the bottle, filling about 1/8 to a 1/4 of the bottle.

2. Add a couple of drops of food coloring and mix.

3. Put the straw in the bottle, (DO NOT DRINK MIXTURE) but don't let the straw touch the bottom.

4. Use the modeling clay to seal the neck of the bottle, so the straw stays in place.

5. Now hold your hands on the bottle and watch what happens to the mixture in the bottle.

Project Explanations:

Just like any thermometer, the mixture expands when it is warmed. This makes the liquid no longer fit in the bottom of the bottle. As the alcohol expands the colored mixture moves up through the straw. If the bottle were to get very hot, the liquid would have come through the top of the straw.

You can watch the thermometer and see how the liquid changes throughout the day. What happens if your thermometer is in shadow or in sunlight? What happens when it gets colder? How does wind affect the thermometer?

In order to accurately read the temperature, you will need to buy a real thermometer that is carefully calibrated for temperature changes. This one is to see how a thermometer works -- just for fun.

Important Safety Note: After you're done with your thermometer, dispose of the liquid properly and rinse the bottle well. Cut it in half, or have a parent cut it in half, so the bottle can't be reused. The used bottle could have some left over alcohol in it, and you don't want anyone to reuse the bottle for drinking water.


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