Rainbow Magic – Science Investigation

This is a firm favourite at our after-school clubs but works well as a primary science investigation! We layer liquids in a test tube but a plastic cup will do just as well.

  1. To start, put the same volume of coloured water, oil and washing up liquid into 3 separate cups. As an extra layer, put golden syrup into a fourth cup.
  2. Predict then test different objects to see whether they float or sink, e.g. marble, a small piece of foam, plastic jewel.
  3. Explain that the liquids have different densities.
  4. Test this by weighing the cups, or even better placing them on a balance to compare them. The washing up liquid is heavier than the water, which is heavier than the oil, even though the volume is the same.
  5. What do the children think would happen if we carefully poured the liquids into the same cup? Clear layers will form: golden syrup, washing up liquid, water and oil.
  6. Give each child a small plastic jewel and ask them what will happen if they drop it into their test tube or cup. Depending on its weight and size (density), it should float on top of the washing up liquid or the syrup but sink in the water.
  7. Children can look around for objects to experiment further. What would sink in oil but float in water? What would float in syrup but sink in washing up liquid? Predict then test!

What’s the science behind this?

The density of an object depends on the mass of the molecules and how tightly packed together the atoms are.

  • Low density e.g. cork – the molecules do not have a lot of mass. The atoms are loosely packed with lots of air in between.
  • High density e.g. metal – the molecules have more mass and the atoms are tightly packed together.