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Home » Science Experiments for Kids » Density Trick with Water

Density Trick with Water

Modified: Nov 20, 2022 · Published: Jul 16, 2020 by Emma Vanstone · This post may contain affiliate links · 7 Comments

This activity is a bit tricky and possibly very messy, but also a fun way to learn about density.

Adding salt to water increases its density, so the less dense plain water sits on top. The two don’t mix.

coloured water science density trick - density trick for kids

What you need

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

Salt Water Density Trick Instructions

Two glasses filled with liquid. The bottom one contains blue food colouring, water and salt. The top glass is plain water. The water glass is on top of the blue water glass with a piece of card in between them.
  • Fill both glasses with water right up to the brim.
  • Add food colouring and salt to one glass and stir well. I didn’t measure the salt but added a generous amount.
  • Put 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 salty 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 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 a card where you can lift a glass of water up and the card stays stuck to it. This is a brilliant 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

Last Updated on November 20, 2022 by Emma Vanstone

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Safety Notice

Science Sparks ( Wild Sparks Enterprises Ltd ) are not liable for the actions of activity of any person who uses the information in this resource or in any of the suggested further resources. Science Sparks assume no liability with regard to injuries or damage to property that may occur as a result of using the information and carrying out the practical activities contained in this resource or in any of the suggested further resources.

These activities are designed to be carried out by children working with a parent, guardian or other appropriate adult. The adult involved is fully responsible for ensuring that the activities are carried out safely.

Reader Interactions

Comments

  1. Pinkoddy

    August 08, 2013 at 1:15 pm

    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.

    Reply

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