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Inside or out, how do we know what the temperature is? We use a thermometer. The word “thermometer” comes from the Greek “therme” for heat and the Latin word “metrum”, meaning to measure. And that’s just what a thermometer does, it measures the heat. Hot or cold, here’s a project you can do to see just how a thermometer works.

• a 16-ounce plastic bottle
• warm water
• food coloring
• a clear plastic straw
• some clay
• a bowl of ice
• a marker

1. Fill the bottle to the top with warm water and add a few drops of the food coloring.
2. Insert 1/3 of the length of the staw into the bottle. Seal the bottle closed with the clay so that the straw is sticking straight up. Watch when you do this and see some of the water go up the straw.
3. With the marker, mark the water level right on the straw so that you know where the water was when you started.
4. Put the bottle in the bowl of ice and observe what happens to the water level in the straw.

Experiments:

• What happens if you put the bottle in a bowl of hot water?
• What would happen if you used different sized items?