science and Technology

What is Density?


Density can be a tricky concept to grasp. Density refers to how much mass there is in a particular space. Imagine a drawer full of socks. It has a specific density. Suppose 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 greater the density of an object, the heavier it feels.

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Solid substances are denser than their liquid and gas counterparts as the particles in a solid are much more closely packed together.

What is Density?

The density of an object is found by dividing the mass of the object by its volume.

Density Formula

Density = Mass divided by volume

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

If the mass is 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.

What is mass?

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.

You can do lots of very cool demonstrations to demonstrate density in a fun, hands-on way.  

Density Demonstrations for Kids

These easy density 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 nifty tricks too!

How to make a Density Jar

honey, golden syrup ( or corn syrup ), washing up liquid ( dish soap ), water and food colouring, vegetable oil

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

First, make a very simple version using just oil and water.

Pour some water carefully into a glass or jar.

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

Carefully drop a 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 the jar? You should find that the oil and water mix up and then separate again.

Simple density column

To make 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, and vegetable oil, in that order.

Density Column Instructions

Density of Liquids

Each of the liquids has a different mass of molecules or different numbers of parts squashed into the same volume of liquid; this makes them have different densities. 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 falls 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 Density Experiments

Homemade Lava Lamp

Homemade Lava lamps are a fun activity demonstrating that oil and water don’t mix.

Density Trick using Salt and Water

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

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

Density and Floating Activities

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

You can also use the same logic to make a lemon sink or an egg float!

Science Concepts






More Awesome Science Experiments 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 you might like!

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 excellent rocket ships, paper spinners and mobile rocket launch pads, all while learning about the scientific concepts behind space travel.

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, finding the perfect ketchup and even creating their own super sour candy powder. It’s colourful, inviting and just brilliant fun.

Last Updated on January 5, 2023 by Emma VanstoneThe post What is Density? appeared first on Science Experiments for Kids.