You’ll need

  • 2 clear drinking glasses
  • Hot and cold water (hot and cold tap water are okay, but boiling and refrigerated water work best!)
  • Red and blue food colouring
  • An eye-dropper (optional, but makes it easier)

What to do

Warning!

Boiling hot water can burn your skin. Ask an adult for help.

  1. Gather your materials on a flat surface.
  2. Fill one glass with cold water and the other with hot water.
  3. Without stirring or moving the glasses, gently add a few drops of red food colouring to the hot water. Add a few drops of blue food colouring to the cold water.
  4. Watch the movement of the colour in the 2 glasses.

Questions to ask

Did the colour move in the same way in each glass?

Try using warm tap water. Does the colour move differently than in the glass with boiling water?

Why do you think temperature affects the movement of the colour?

What's happening

Heat is a type of energy. The hotter something is, the faster its particles (atoms and molecules) are moving.

The molecules in hot water move faster than the molecules in cold water. This means the food dye molecules spread out faster in the hot water.