Ever wonder how thermometers work? The science of thermometers is simple. Higher temperatures produce greater levels of energy, which allow molecules to move faster. You can see this in action by placing a straw inside a bottle filled with liquid. When the liquid gets hotter, it is sucked up farther and farther into the straw. Using a digital thermometer you can then measure how hot it is by determining where the liquid sits inside the straw.

It’s a super simple science activity, but you can learn a lot!


  • Bottle
  • Straw
  • Clay (play dough also works)
  • Rubbing alcohol
  • Water
  • Food coloring
  • Permanent marker
  • Digital thermometer

Making A DIY Thermometer

  1. Fill a third of the bottle full of a mixture of 50% alcohol and 50% water. Dye the liquid red or another fun color so you can easily see the level inside the straw.
  2. Suspend the straw inside the bottle with clay, leaving a small amount in the water, but don’t allow it to touch the bottom of the bottle.
  3. Make sure the top of the bottle is sealed with clay.
  4. Set the bottle outside and track its temperature with a digital thermometer.
  5. The hotter the bottle gets, the farther up the liquid reaches inside the straw.
  6. After examining how high the liquid reaches at each temperature reading, mark the lines of each temperature on the bottle with a permanent marker.