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KS1 Science at Home: Week 10

Key Stage 1 Experiment of the Week – Which travels faster, hot water or cold water?

How does it work?

This experiment is great for testing if hot water molecules really move faster than cold ones. Pour some water, drop in some food colouring and compare results. If you watch closely you will notice that the food colouring spreads faster throughout the hot water than in the cold. The molecules in the hot water move at a faster rate, spreading the food colouring faster than the cold water molecules which move slower.

Materials you need

  • A clear glass filled with hot water
  • A clear glass filled with cold water
  • Food colouring
  • An eye dropper


  1. Fill the glasses with the same amount of water, one cold and one hot.
  1. Put one drop of food colouring into both glasses as quickly as possible.
  1. Watch what happens to the food colouring.