Density can be a tough concept to grasp. Density refers to how much mass there is in a particular space. Imagine a drawer full of socks. It has a certain density. If you take a sock out, the density of the drawer changes. This is because the mass of the socks has changed, but the volume of the drawer has stayed the same.

Generally the more dense an object is, the heavier it feels.

What is Density?

Density Formula

Density = Mass divided by volume

The units used vary depending on the units of the mass and volume used for the calculation.

If the mass was measured in kg and volume in cm³ the units for density would be in kg/cm³

Something else that can be confusing is mass. People often talk about weight when they mean mass and vice versa.

Mass is a measure of how much matter an object is made up of. The mass of an object remains constant unless you add to or remove part of it.

The weight of an object depends on gravity. Your weight would be less on the moon as there is less gravity, but your mass would stay the same.

There are lots of very cool demonstrations you can do to demonstrate density in a fun, hands on way.  

Density Demonstrations

These easy demonstrations are super simple and brilliant fun ways to show kids ( and grown ups ) this tricky concept in action. There are also a couple of cool tricks too!

How to make a Density Jar

Liquids layered on top of each other to make a colourful density column #densityjar #densitytower #densitycolumn #densitydemonstration

Image taken from This IS Rocket Science

What you need to make a density column

Vegetable or sunflower oil


Food Colouring

Washing up liquid


Golden Syrup

LEGO or other small objects.

How to make a density column

Pour some water carefully into a glass or jar.

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

Carefully drop couple of small objects into the mixture and observe what happens. Can you find an object to float on each layer?

What happens if you shake it the jar? You should find that the oil and water mix up and then separate again.

To make a a density column with more layers like the one above, you need lots of different liquids of different densities.

We used: honey, golden syrup ( or corn syrup ), washing up liquid ( dish soap ), water and food colouring, vegetable oil in that order.

Density of Liquids

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.

More Experiments

Homemade Lava Lamp

Homemade Lava lamps are a fun experiment to demonstrate the fact that oil and water don’t mix.

Homemade lava lamp to demonstrate density.

Density Trick using Salt and Water

Show your friends a science magic trick and fantastic density demonstration. This uses salt to change the density of one colour of water.

Two glasses on top of each other filled with water, food colouring and different amount of salt. One colour floats on top of the other.  Salt and water density trick

We also have a pirate themed density bottle. Pirate treasure is perfect for hiding in the layers.

underwater themed density bottle - amde with blue water and oil

Density and Floating

Did you know that if you reduce the density of an object that sinks in water it will float? We did this with a heavy ball and used bubble wrap to make it less dense.

You can also use the same logic to make a lemon sink….

Easy Density demonstrations for kids. Make a density column, change density with salt and more. What is density? #density #densitydemonstrations #densityexperiments
Easy Density Demonstrations for Kids

Don’t forget we have 100s more fun and exciting science experiments for kids on Science Sparks.

Some of my favourites are our Fairy Tale Activities where you can make a raft for the Billy Goats and a Zip Line for Jack and the Beanstalk. The infamous coke and mento explosion is always great fun to watch and our water science experiments will keep you busy for weeks!

Wherever your interests lie, you’re sure to find something you like in our vast collection of science experiments and investigations.

Science Books from Science Sparks

I also have a couple of science books available.

This IS Rocket Science

This Is Rocket Science includes 70 fun experiments for kids (and adults ) showing  you how to use everyday items like bottles, cardboard, glue and tape to build awesome rocket ships, paper spinners and mobile rocket launch pads, all while learning about the scientific concepts behind space travel.

Image of This Is Rocket Science book
This IS Rocket Science

Snackable Science

Snackable Science contains 60 edible experiments allowing kids to investigate their way around the kitchen making magical mixtures, edible Jenga and Tetris, find the perfect ketchup and even create their own super sour candy powder. It’s colourful, inviting and just brilliant fun.

Snackable Science Experiments for kids - edible science book

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Originally posted at Science Sparks