WATCH: A fun and easy way to explain density by creating a seascape in a jar


When we talk about density, we refer to the amount of space an object or substance takes up (volume) in relation to the amount of matter in that object or substance (mass). We work it out by dividing the mass of an object by its volume (ρ = m/v).

This tells us that a heavy and compact object is high in density, or a light and big object is low in density.

This is a scientific concept that seems difficult to explain, but we can simplify comparisons of density by measuring which substances sink (because they are heavier, and therefore denser) and which float (because they are lighter and less dense). Visualising it may make it a little easier to understand.

We’ve put together a little something to do just that. Using a beautiful seascape and liquids of different densities, watch the video above for a quick and easy science experiment and scroll down for how best to explain the concept to the kids.

Here’s how:

  • Jar
  • Sand
  • Water
  • Blue food colouring
  • Oil
  • Shaving cream
  • Ocean toys (we used little fish)

Add blue food colouring to the water. Slowly layer your jar in the following order: Sand, blue water, and oil; add shaving cream to the top, and then drop in the plastic or rubber toys one by one. Let the kids watch how the substances mix at first before settling in layers.

science experiment explaining density

Here’s how to explain it:

The denser an object or liquid, that is the heavier and more compact it is, the more likely it is to sink when compared to an object or liquid that is less dense. 

In our experiment, the sand was the most dense, then the water, oil, and finally the shaving cream. Although they mixed when first added together, they eventually separated because they have different densities.

When we added the fish, we could also see how dense they were in relation to the other layers be seeing how far they sank or floated.

Are there any other simple and easy experiments you've tried at home to teach your kids particular concepts? Send us your ideas to

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