Hot vs Cold Water Experiment

We have a super cool water experiment that’ll teach your child about temperatures! Parental help may be required.

What you’ll need:

  • Two wide-mouthed jars must be identical (we recommend baby food jars)
  • Water
  • Spoon
  • Food colouring (the experiment uses red and blue but any two colours will work)
  • Index cards or squares of wax paper (must be about 3x3inches)
  • Sink or baking pan 

Step 1

Fill one of the jars with very hot water. Add a drop or two of red food colouring. Give it a quick stir with a spoon then set it in the sink.

Step 2

Fill the other jar with very cold water and add a drop or two of blue food colouring. Give it a quick stir with a spoon. Make sure this jar is completely full. It needs to be at the point where the water bulges on the rim of the jar.

Step 3

Lay a 3x3inch square card over the top of the blue jar. Tap the card around the rim of the jar. This should create a seal with the water and jar. 

Step 4

This step can be tricky! Pick up the blue jar and flip it up-side down over the sink. You have to do this very quickly or else the water will spill out! The car should be suctioned to the jar so you won’t need to hold it with your hand.

Step 5

Put the up-side down jar right on top of the red jar. Make sure they are perfectly lined up!

Step 6

With a parent holding the top and bottom jars steadily, pull out the card slowly. Observe the changes that you begin to see! What are the colours doing? Why do you think this is happening?

Step 7

Repeat steps 1-6 again but this time put the red jar on top of the blue jar instead. When you pull the card what happens? Do you notice anything that’s different?

The STEM Behind the Fun!

You may have noticed that the hot red water moves when it is on the bottom opposed to when it is on the top. It moves to the very top because heat rises! When water is heated the molecules start to move fast and bounce around creating more space between them all. Due to there being more space, hot water weighs less than cold water! The water turns purple quickly because as the heated molecules travel up above the cold, it pushes some of the blue around with it.



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