What does Density mean? – Floating and Density

Science sparks are very excited to share another fun science activity today, this time it’s a fun and super simple demonstration of density.

What does density mean?

We’ve made a rainbow glass before, but today we are doing a much more simple version and adding a bit of LEGO. This is a really cool demonstration to explain the concept of density.

What you need

Vegetable oil


LEGO or other small objects.


Pour some water carefully into a glass or jar.

Very carefully add about the same volume of cooking oil on top.

Then drop a couple of small objects into the mixture and observe what happens. Can you find something to float on each layer?

What happens if you shake it?


The science bit

Each of the liquids have a different mass of molecules or different numbers of parts squashed into the same volume of liquid, this makes them have different densities and therefore one can sit on top of the other – the more dense a liquid is the heavier it is.

Objects and liquids float on liquids of a higher density and sink through liquids of lower density. The LEGO brick  sinks through the oil but floats on the water, while the coin sinks through both. The coin is therefore more dense than both the oil and the water. The plastic bug floating on the oil is less dense than both.

Other density activities on Science Sparks

Summer Density

Some density magic


Author: Emma Vanstone

Science Sparks, is a site dedicated to making Science fun for kids. I’d love you to follow me on my Google Profile+.

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  1. Fabulous. I love the easy way you’ve explained it. Pinning to my science board :)

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    • do let us know if you do it. x

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  2. So cool!! I love it. Thank you for sharing on Sharing Saturday!!

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  3. Another great demo for teaching density would be with pop. What you need is a fish tank full of water, a diet coke, and a regular coke. When you put the two cans in the water, the diet coke will float and the regular coke will sink. Explain to the kids that since the diet coke does not have as much mass, it is less dense so it floats.

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