Eureka science


This activity looks at famous Greek inventor and scientist Archimedes. You can try out one of his experiments as well as having an interesting writing activity

How it works

Read about Archimedes’ bath experiment, which made him famously shout ‘Eureka!’

There are two versions of this experiment you can try. One is more basic and the other slightly more challenging. Try one or both of them and then choose a follow up writing activity.


Archimedes and his famous bath

Archimedes was a famous scientist in Ancient Greece. The king once asked him to help him with a problem. The story goes that the king had given a goldsmith a piece of gold to make him a crown. When he got his crown he suspected the goldsmith of cheating him. He thought the man had stolen some of the gold and mixed in some silver in its place. But he couldn’t prove it, so he asked Archimedes to help.

Archimedes struggled with the problem for a while. One day he got in his bath and as the water level rose. Archimedes had a moment of realisation. He leapt out of the bath and ran down the street (without stopping to put his clothes back on!) shouting ‘Eureka’, which means, ‘I have it’.

What Archimedes realised was that his body displaced (replaced and moved) the same volume of water as the volume of his body. He realised he could do the same thing with the king’s crown, a piece of gold and a piece of silver.

Archimedes did an experiment to find out how much water the silver, gold and the crown displaced. He then used maths to work out if the crown was pure gold or if there had been silver added to it.

Unfortunately for the goldsmith, Archimedes’ experiment worked and it proved the king’s suspicions right. The crown wasn’t pure gold and the goldsmith had mixed in some silver.


Try one of the versions of Archimedes’ experiment by following the instructions below.

When you have finished your experiment write a letter to the king informing him of what you have found out.


  • Write a diary entry as Archimedes

It could be about his Eureka moment in the bath (and embarrassment at running down the street with no clothes on!)

Or about doing the experiment and how you felt when you discovered the truth.

Or include both


  • Make a comic strip or write a short extract about Archimedes doing the experiment. You could write it pretending to be Archimedes.


  • Write the whole story of Archimedes and the golden crown in your own words or make the scenes from Lego, modelling clay or plasticine.



Archimedes’ Golden Crown Experiments

Below there are two experiments. One is a simple experiment to understand more about how water is displaced by an object. The other experiment is more advanced and will help you discover the density of objects.

For these experiments you’ll need to use different objects to Archimedes… unless you happen to have a lump of gold, a lump of silver and a king’s crown!


Simpler experiment

You will need:

  • A container like an empty ice-cream tub
  • Water
  • Various objects that will fit in your container


1. Half-fill a container with water

2. Put an object in the water and see how the level rises

3. Try different sized objects and see the different amounts they push the water level up.


This is what made Archimedes realise he could use this information to work out if the crown was pure gold or not.


Advanced experiment

You will need:

  • Weighing scales

  • Measuring jug

  • Water

  • A variety of objects (they must be small enough to fit in your measuring jug – we found different types of rocks worked well)

  • A calculator


What to do:

  1. Weigh your object on the weighing scales and make a note of how many grams it weighs (you might need to just make a best guess if you don’t have accurate scales). This is the object’s mass.
  1. Fill your measuring jug with enough water so that when you put your object in it is fully submerged. Remember to note where the water starts from – we started at 200ml.
  1. Put your object into the measuring jug. Look at where the water goes up to now. Make a note of the difference – how much the object has pushed the water up. For example if the water line is now at 300ml and you started at 200 ml, the difference is 100ml. This difference is the volume of the object. Make a note of this number. In this example the object’s volume was 100ml.
  1. Now get your calculator. Archimedes’ sum to work out the density of an object is Mass / Volume. Let’s say the object you are looking at weighs 200g and its volume is 100ml. The sum you need to do is 200/100. The answer is 2. We now know the density of the object is 2g/ml.

5. Try this with your different objects and compare their density. Do any surprise you?

Archimedes worked out the density of gold, the density of silver and the density of the king’s crown. He knew the density of gold would be the same whatever the size of the piece of gold. The crown had a different density to the lump of gold and that’s how Archimedes proved it was not made purely of gold, but had some silver sneaked in there.


Confused about density?

All objects are made of molecules.

The more tightly packed together the molecules are, the denser the object is.

Think of a busy city and all the people packed in close together. The people are like molecules and the city is the object. This object would be very dense.

Now think of a big open field with only a few people on it. This is like an object that has a very low density with lots of space between the molecules.

By working out the size of the city and the amount of people in it, you can work out its density. In a similar way by finding out the volume of an object (by working out how much water it displaces) and by knowing how much the object weighs (what its mass is), we can work out the density of the object.


Want to know about more of Archimedes’ discoveries and inventions? Watch this clip on BBC Bitesize: