The Cartesian Diver

From TecHKnow Wiki
Jump to navigation Jump to search

The Cartesian Diver

Using a large beaker put the diver into the beaker of water. It should float upright with the open end of the straw at the bottom. When you have got this right, transfer to the 2 litre bottle

This scientific toy is named after the 17th Century Philosopher Rene Descartes. The diver floats or sinks at your command by squeezing or releasing the bottle. The practical is great intro for Science Clubs and should take no more than 30 minutes to set up by students. The technician should trial out the experimetn beforehand. One interesting trick to ensure that it works on the day is to use a "gluegun" to seal with glue the straw at one end. Sometimes the blutak does not do this too well.


  • A 2 Litre Drinks bottle and cap
  • A Plastic drinking straw
  • Blu Tak
  • 600 or 800ml Beaker

Hazards None. But High messy level with water!


  • Fill the drinks bottle with water to the very top
  • To make the diver, cut a piece of straw 5cm long. Plug one end with a small amount of blutak. Roll out another short length of blutak and wrap it around the other end of the straw.
  • Put the Diver into a beaker of water, it should float upright with the open end at the bottom
  • Adjust the amount of blutak until it just floats with only the very top of the straw bobbing out of the water.
  • When the diver is floating properly transfer it to the Drinks bottle. Make sure that the bottle is topped up and put the cap on tight.[/*]
  • Squeeze the bottle and the diver should sink. Release and the diver should rise.

Here comes the Science

This experiment demonstrates the property of buoyancy. An object is buoyant in water due to the amount of water it displaces or 'pushes aside' As you squeeze look carefully at the straw. You should see the water level inside it rise. This is because the bottle is completely full of water. When you squeeze the only gas (bubble) that you can compress is inside the diver. So more water enters the diver, making it heavier so it sinks. Submarines use a similar principle to control their buoyancy, as do some fish

568 4d3972151c93f.jpg Marcus Rowland has suggested the following:

Try a plastic pipette with a nut around the nozzle to weigh it down. Quite easy to adjust the air volume 
(you just squeeze most of it out while the end is  In water) and made very quickly.


It's not strictly making unopened sachet of ketchup works just as well. 

--Ssmith 11:12, 26 September 2012 (BST)