The Cartesian Diver experiment involves a bottle of water (preferably plastic!) and a glass test tube. It demonstrates simple principles of pressure.
- Fill your bottle completely with water.
- Fill the test tube partway with water.
- Carefully submerge the test tube into the bottle (opening face down).
- Make sure the bottle is completely filled and then secure the cap.
- You may now 'operate' the experiment by squeezing the bottle with varying degrees of force.
- When you do so the pressure inside the bottle will increase (as its volume decreases).
- The water is incompressible, and the only substance less dense that the water is the air inside the test tube.
- Hence it is this water that is compressed into a smaller volume.
- Less of the test tube is filled with air, and more of it is filled with water!
From here we have two ways of consideing the situation:
Consider the test-tube and air as your system.
- Weight stays the same.
- As you squeeze the bottole, the volume of water displaced decreases.
- Thus upthrust decreases.
- Take into account that: Resultant force = Weight - Upthrust
- Weight is constant as mentioned above.
- Therefore the (downward) resultant force increases!
- BING: Your diver sinks lower!
Consider the entire test-tube (with air and water) as your system.