Floating and sinking is all about density. We usually think about solid things floating or sinking in water. For example, a football will float on a pond as it is less dense than water and a bowling ball will sink as it more dense than the water. Using these same ideas about density you can make liquids float on top of each other with some very colourful results!

You need

  • a glass or clear plastic beaker
  • golden syrup (squeezy bottle is best)
  • washing up liquid
  • coloured water (use food colouring or fruit squash)
  • cooking oil
  • a spoon

What to do

First, pour about 1cm of golden syrup in the bottom. Try to avoid getting any on the sides of the glass. Next, carefully pour washing up liquid on top (try to pour it very slowly down the side of the glass). Do the same with some coloured water, even slower this time. Finally pour vegetable oil slowly onto the top, it’s easier if you run it over the back of a spoon. Hey presto, you’ve made a liquid rainbow, isn’t it pretty?

Think like a scientist:

  • What happens if you carefully pour a few drops of coloured water on top of your rainbow? (watch from the side)
  • Can you experiment with other liquids?
  • You can try making your own liquids of different densities by adding different amount of salt or sugar to water.
  • Which liquids are best for floating? Try floating the same thing in different liquids such as water, oil, juice, washing up liquid, golden syrup. Do some things float in one but not the other? Can we link this to the density of the liquid (think back to the rainbows)? This is a messy one but does you thinking about density! Good things to try are peas, small beads, marbles and sweets.

Don’t forget to show us your rainbows on the Fab Science Facebook group…we’d love to see what you have been up to!