Today’s activity is super simple, but very impressive and a great little salt water science density trick to show your friends!

coloured water science density trick - density trick for kids

What you need

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

Salt Water Density Trick Instructions

Density trick for kids
  • 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.

density trick for kids

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.

Density trick - science for kids

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

Cool science for kids - density trick

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.

More density examples

Make a creepy density jar for Halloween.

Find out how to make a water balloon sink

Discover why apple bobbing works

Try an easy floating and density trick.

Finally, try some sinking and floating to learn about density.

What’s your favourite density trick?

Salt and water density trick for kids - why doesn't salty water and normal water mix? #scienceforkids #scienceexperiments  #densityforkids

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Originally posted at Science Sparks