When you think of a thermometer, you might imagine a thin glass tube with mercury, but it turns out we can make our own thermometer with items that are mostly found just around the house.

Our thermometer is going to be liquid based as thermometers have been for hundreds of years. The liquids that we’ll use are water and rubbing alcohol. You want to use the same amount of each, such as a half cup. Make sure a parent is around for this part.

Add some food coloring. Red is an obvious choice because most thermometers use red liquid. Just a couple of drops will do it.

Next, we need a clear straw and some mold in clay or Play-Doh. We want to shape our Play-Doh around the straw to close the opening over the bottle. Seal the Play-Doh over the opening tightly. We want the only air moving in and out of the bottle to have to travel through this straw. The clay also holds the straw in place. We want it in the liquid, but we don’t want it to touch the bottom.

Now, we’re at the point for what this thermometer is all about. The level will change with the temperature. As the temperature rises, the air expands, and that’s going to push the liquid up the straw. When it gets colder, it contracts, which leads to a lower level on our thermometer.

We’ll use ice cubes to get the temperature near freezing. Set the thermometer in a bowl and add water and ice cubes. This will take a bit, so you’ll have to wait a couple of minutes. You can use an actual thermometer to confirm the temperature and mark it on your bottle. This is called calibrating our thermometer.

Do the same thing with warm water. Once the level is no longer rising, mark that on your thermometer. You can calculate the full scale by measuring the distance between the two marks. In my case, my thermometer bottomed out around 46°F and topped out at 91°F. There were 6 centimeters between the two points. This means my thermometer rises 7.5 degrees rise per centimeter.

Now you have your own thermometer! You can take it around the house, and the cool spots are where the thermometer falls. The warm spots are where it rises.

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