Hot and Cold Water Science Experiment

Hot and Cold Water Science Experiment


  • A large transparent bowl or vase or jar
  • A bottle containing very hot tap water or boiling water
  • A bottle containing very cold water, placed in the refrigerator prior to the experiment
  • Red and blue food colouring


  • Be careful! Hot water can burn you! Do this experiment with an adult’s help.
  • Add a few drops of red food colouring to the bottle containing hot water and a few drops of blue food colouring to the bottle containing cold water.
  • Pour water from the cold water bottle into the vase until it is half full.
  • Gently pour hot water onto the cold water. Watch what happens!

How did the magic happen?

Certain liquids are less dense than others. But water has the same density as other water, right? So why does it stay separated? So understand this! The secret is in the temperature of the water. The molecules in hot water move faster than those in cold water. Hot water molecules bounce around and leave gaps. This makes hot water slightly less dense than cold water. So when you put the cold water on the bottom, the denser cold water stays there. The water particles in the cold water are much closer together and it therefore appears to be heavier. On the other hand, the water particles in the hot water are farther apart making it lighter and therefore allowing it to float on top of the cold water.

By Tapasya Aggarwal,

Class V, Amity International School, Gurugram