Continuing our kid-friendly, STEM-supplementing series of easy to make weather instruments, Stormtracker 18 has how to make a homemade thermometer.
Here's what you'll need: 1) an empty soda or water bottle of any size, but 20 or 24 ounce bottle probably works best when compared to the size of 2) a clear straw, 3) food coloring, 4) modeling clay or Play-Doh, 5) an index card, and 6) clear tape. Optional: a real thermometer for reference.
Step one: Fill the bottle up about 80% with room-temperature water and food coloring. (not all the way up). Let sit an hour or so to make sure water has matched the air temperature.
Step two: Have modeling clay or Play-Doh ready and drop the straw into the bottle, but make sure it doesn't completely fall in. You want the water to have a couple inches to move up as temperature increases.
Step three: Place a finger on the top of the straw to seal it, and then lift the straw so the bottom is about 1/2 to 3/4 way into the water. Secure it in place with the modeling clay or Play-Doh. Make sure the clay or Play-Doh also seals the top of the bottle so no air can enter bottle. When you take finger off, the water should stay in place in straw.
Step four: Mark a line on the index card, and tape it behind the straw. Use another thermometer to check air temperature near your new thermometer. Record the temperature on the index card with the line matching the top of the water. Keep checking thermometer in slightly different temperatures (though readings from any thermometer in direct sunlight will not be accurate and will read too warm). You can add more lines and labels on the index card as the temperature changes.
We have more make-at-home experiments and will have them all in one place HERE, so check back often as we continue to add them.