Homemade Thermometer

We use thermometers all the time.  We measure the temperature outside so we know whether or not to wear a jacket, the temperature in our oven as we bake, and our own body temperature when we think we might be getting sick.  They are simple devices, but incredibly useful ones.  You can make a model homemade thermometer to show how thermometers work.  All you need are a few everyday household items.

You’ll need:

  • a clean, clear, empty water bottle
  • a clear straw
  • play-doh or clay
  • rubbing alcohol
  • water
  • a hair dryer (or tubs of very hot and very cold water)
  • red food coloring (optional, but it makes the liquid level more visible)

Supplies for making a homemade thermometer Here’s what you do:

Start by filling the bottle halfway with water.  Fill the remaining half with rubbing alcohol.  We added red food dye at this point to dye the water and alcohol red so it would be more visible as the liquid level changed.

Building a homemade thermometer Use the clay to surround the straw and then press the clay on to the top of the bottle, completely sealing it so it’s airtight.  Make sure the bottom of the straw is about an inch from the bottom of the bottle, allowing the red liquid to rise up it.

Now your thermometer is ready.  We’ll apply heat to the liquid and watch the “mercury” (we don’t have mercury of course, just red dyed alcohol water, but it is acting as our mercury in this experiment).   To apply heat you can just turn on your blow dryer and let it blow on the bottle for a few minutes, warming the liquid inside.


Alternately, you can place your water bottle thermometer into a tub of very hot water to heat it.  (Afterwards you can put it into cold water to watch the liquid come back down the straw.)

As you heat the liquid, you will be able to watch it climb higher and higher up the straw with the increase in temperature.

The temperature is rising on our Homemade Thermometer

Of course, as it cools off, it will go back down the straw, lower and lower.

The Science Behind Thermometers:

Galileo thermometer
Galileo Thermometer, public domain

The first thermometer was invented by Galileo sometime around 1593.  He made it based on the premise that hot air expands and cold air contracts.  His thermometer was quite different from our current model.  He used a thermoscope, which had bulbs of liquids floating in an outer tube.  The more heat it was exposed to, the more bulbs would rise within it.

In 1714 Gabriel Fahrenheit invented the reliable version of a thermometer that we currently use.  It is based on that same premise – as the alcohol in your thermometer increases in temperature, it expands, forcing the liquid up the straw.  As it cools, the molecules contract and you see it go back down the straw.  Early thermometers used water, but that meant we couldn’t measure anything below the freezing point of water.  Alcohol has a lower freezing point, so it’s more suitable.  Fahrenheit arbitrarily decided there should be 180 degrees between the freezing and boiling points of water and set the freezing point of water  at 32 degrees and the boiling point of water at 212 degrees.

The red line inside of a thermometer goes up when it gets hotter because the liquid inside (either alcohol or mercury usually) is expanding as it gets hot.  The liquid has nowhere to go but up, so it goes up.  As it gets colder and contracts, the little red line goes back down.  That’s exactly the same thing you are seeing happen in your water bottle and straw homemade thermometer.


Additional Layers:

  • Find out about other temperature scales.  Fahrenheit decided on his own scale, but later Anders Celsius created another scale with the freezing point of water at zero degrees and the boiling point at 100 degrees.  Lord Kelvin created the Kelvin scale even later than that, and also introduced the idea of absolute zero, or the point at which there is no heat present at all.
  • Make a scale for your homemade thermometer by using an index card behind it and marking off evenly spaced increments.
  • Set up a weather station outside.  You can start with the other weather experiments from the earth science section on Layers of Learning.  We record the weather every morning as part of our morning calendar routine.  We graph the temperatures and kinds of weather we’re experiencing, make predictions, and compare the weather forecast with the actual weather.
  • Write weather poems.  Choose a weather phenomenon to vividly describe.  You could also write one about the sky and expound on all the things that fall from the sky.
  • Learn the root words that make up the word thermometer.  “Thermo” means heat and “meter” means measure.

More From Layers of Learning:

Check out these five units from our catalog.  Each one has a weather-centered science section filled with projects and experiments to make your weather study fun and memorable.

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