More Density and Some Science Magic

Today’s activity is super simple, but very impressive.

Science density

What you need

  • 2 glasses the same
  • A piece of card
  • Food colouring
  • Salt
  • Water


  • Fill both glasses with water, right up to the brim.
  • Add food colouring and salt to one glass. I didn’t measure the salt, but added a generous amount.
  • Place the card over the glass containing just water and carefully place it over the glass of coloured water and salt.
  • Even more carefully remove the cardboard.


Why doesn’t the water mix?

The salt water has a higher density than the plain water, and so stays at the bottom.

You can see here what happens if you don’t add the salt. The plain water mixes with the coloured water.



If you put the salt water on top, it all mixes, this is because the more dense salt water tries to move down to the bottom.


I would recommend doing this over a sink, or somewhere you don’t mind getting wet.

Density activity

Mom to Posh Little Divas did an activity last week with water and card where you can lift a glass of water up and the card stays stuck to it. This is a demonstration of air pressure, and would be great to do at the same time as this activity.

Other density posts.

Summer Density

Creepy Density

Make a water balloon sink

Apple Bobbing

Floating and density

Sinking and Floating

You can see the first two weeks of Spectacular Summer Science here.

There are 7 comments

  1. Pinkoddy

    Oh I shall do this with my boys – they will be very impressed I think. But need a time when youngest isn’t about I think. Thank you for sharing, not only the idea, but the science behind it.

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