Convective Heating
Energy and Thermal Physics

Hot Water Rising

At home for 5-11 11-14

What you need

  • Two plastic drinks bottles
  • Cold water
  • Hot water
  • Sink
  • Piece of card
  • Red food colouring


  1. Fill one bottle with cold water and the other with hot water from the tap. Add some red food colouring to the hot water
  2. Hold the card firmly over the top of the cold water bottle, turn it upside down and balance it on top of the hot water bottle
  3. Align the bottles and carefully remove the card. Do this in the sink just in case!

Results and Explanation

Hot water is less dense than cold water so it rises into the top bottle while the cold water sinks into the bottom bottle. This convection continues until the water is the same temperature throughout both bottles.

These experiments have not been specifically safety tested for home use but we believe them to be safe if the instructions are followed. Adult supervision or direction is recommended as appropriate. All experiments are carried out at your own risk.

Convective Heating
is a special case of Heating

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