Sunday 19 May 2013

Archimedes' bath

I rewrote this tonight because I realised it needed updating: some links didn't work and I wanted to update it with new things we've thought up recently.  I have changed the date too as it really is ten times more than it has been.

This one you can include some maths and history, if you want to learn more about Archimedes, as well as science.  This is always a bonus in our house; my girls love when they get several subjects done in one.  Honi when she was 4 year old even tried to join in with this one as I'm 100 percent sure she would now.

We did this experiment at one of the HE groups a quite a while ago now.  That is when I first thought of this I thought: lets make it into a fun project!

For this history part, and literacy, it is a story after all, found this link about Archimedes and the story to the discovery of Archimedes principle.  My girls loved it the first time I read this to them.  They spent the night running round shouting 'Eureka!' and explaining to their dad that Archimedes ran all the way home nudey rudey!  I think they thought that was the best bit!  I loved that this covered history as well as the science last time and I'm looking forward to seeing their faces when we do it again (I'm sure the older ones will join in when I start the project with Honi)!

I made a easy to make homemade Archimedes bath for our HE group nearly 2 years go. 

All you need is:

  • An ice cream tub
  • Some blu tack
  • a straw
  • A jug (preferably a measuring jug)
Use some scissors to make a hole for the straw to just squeeze through about half way up your tub.  (I guess you could use a drill, or a sharp pencil, whatever you method you choose, please be careful). 

Squeeze the straw through the hole so it looks something like in the photo - use the blu tack or modelling clay to seal any gaps between the outside of the straw and the small hole in the ice-cream tub.

The straw will be the overflow so you will need a jug to catch the water that overflows out.  It is best to have a measuring jug then you will see exactly how much water is displaced without the need of maths, apart from reading the measurement of course. 
If you are wanting to measure the volume of something you will want to push it down so it is fully submerged.
Here it is:

Oh and don't forget the jug!  A measuring jug's best as you can then directly measure the exact volume of the object you have submerged in the water!

If you are doing it with very young children you might want to just play with it.  Use a jug but don't worry about exact measurements.  Place a potato in the water, talk about how much water is in the jug. 

You will find that the volume of the water displaced will be the same as the volume of the potato, this is because with Archimedes principle, the volume of water displaced is the same as the volume of the object that displaced it.

Take out the potato, replace the water from the jug into the ice cream tub then put in an orange or an apple, or any object you like that can be fully submerged in your ice-cream tub.  Again measure how much came out, measure the volume of water that was displaced and talk about whether there is more or less or the same amount of weight of water in the jug as there is in the object submerged. 

Repeat this until the child becomes bored or you have to be somewhere just because it is FUN!
Another method is Archimedes' bucket but it is harder to measure the water and compare it to the volume of the object.
To do this you will have to have:
  • a bucket (a cheap kitchen bucket would do)
  • a pen that is a colour that will show up clearly against the colour
  • water
Now all you will need to do is put into your bucket whatever it is you want to find the volume of, your toy dinosaur, an orange, an inflated balloon!  Make sure it is fully submerged and then take the reading of how high the water has raised (this tells us how much water has been displaced), now subtract the reading without the object in the water from the risen water and you will have the volume of the object.
When we say displaced we mean the water that has moved to fit round the object. Archimedes discovered through this that:
buoyancy = weight of displaced fluid
Archimedes' principle is true of both liquids and gases which is why this works.
Have fun.  I hope this is helpful to someone out there.
EXTRA FUN:  A friend of mine, Richard, pointed something out to me.  He said that if we were to submerge the potato we could discover it's volume this way but if we then put the potato in a 'boat' and weighed the water it displaced it would equal the weight of the potato. 
I will be trying this soon, thank you muchly Richard.


  1. My kids and I love the children's picture book 'Mr Archimedes Bath' by Pamela Allen where Mr Archimedes can't work out who - of all the strange animals he is sharing a bath with - is making his bath overflow. Lovely illustrations too :)

  2. Brilliant thanks for sharing that. I will look for it on Amazon now! x