Experiment: Build your own thermometer!

Warm water needs more space than cold water — check it out in this experiment!

You will need:

  • 1 small plastic bottle
  • 1 drinking straw
  • modelling clay / play dough
  • Food dye (not strictly necessary, but more fun)
  • A large, high container in which the small plastic bottle can stand
  • cold and warm water

Fill the bottle with cold water (and add a couple of food dye if you like). The bottle should be completely full, so full that it is almost overflowing.

Place the straw in the bottle and lock the bottle with modelling clay. At least 10 cm of the straw should be left above the lock! Test that the lock is water tight by slightly pressing on the bottle. Water should now be rising in the straw, but not spilling out of the lock! It is not easy to get the lock completely watertight, you might need several attempts.

Now place the bottle in the larger container and fill the container with hot water (careful – don’t hurt yourself!). Wait a couple of minutes and observe what is happening. How high is the water rising in the straw?

Now put really cold water in the larger container instead of the hot water. What happens?

Try this for different water temperatures – lukewarm, really hot, medium hot, cold, etc. What happens now?

Researchers have found out that the water in the deep ocean is slowly warming. What do you think the consequences will be?