Density tower

posted in: Skill Based, STEM! | 0


15-20 minutes

Estimated Cost:

Under £5

Focus object floating in liquids of different densities

Shock and delight your kids with the wonders of liquid density.

Things you’ll need

Tall glass or small vase


Food colouring

Cooking oil


Small items from around the house. We recommend peas, a coin and a ping pong ball for the best results, but you can add any other items you like!



Prepare your liquids! Bear in mind that measurements will vary depending on the size of your glass – don’t forget to leave a bit of space at the top so it doesn’t overflow when you start adding things.

  • Mix food colouring into water.
  • Dissolve a teaspoon of sugar (honey or syrup work too) into hot water and allow it to cool.
  • Measure out 50-75ml of oil.


Pour all three liquids into your tall glass, starting with the sugar syrup, then the water and finally the oil. Pour slowly to avoid the liquids mixing and you should see three clear layers.


Try dropping items in one by one. Where do they rest? You should see that different items stay in different layers of the liquid.

Items to try in addition to your pea, coin and ping pong ball could be a pumpkin seed, a bottle cap, a rubber, a dice or some beads. Anything goes as long as you don’t mind it being covered in the liquids!


The taller your glass, the more liquids you could try adding. You could experiment with washing up liquid, milk or undiluted honey.


The science at play here is that if an item is less dense that a liquid, it will float. We see this all the time with rubber ducks in the bath.

However, liquids have density too. Here, some of the liquids are more dense than the others, creating the layers. The most heavy liquid is on the bottom and the least is on top.

Some of the items are heavier than some of the liquids, but not others. This is why some sink all the way, some sink only part way, and others float on top!

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