Build a Cartesian diver.
How does it work?
This is all about density. When the diver floats, there is a volume of air trapped inside, when the bottle is squeezed, the air is compressed but the water is not. The volume of air trapped decreases, and the displaced water reduces. The diver loses buoyancy, and sinks. When the pressure on the bottle is released, the air expands, displaces the water and the diver floats.
Design icons
Submarines are surrounded by ballast tanks, which help control their buoyancy. When filled with water, the tanks increase the density of the submarine and it sinks. When the submarine needs to rise, the water in the ballast tanks is replaced with compressed air.
Ingredients:
- Drinking straw cut to 1in in length
- Modeling clay
- A two liter bottle
- A drinking glass and water
STEP 1
Put a small ball of modeling clay on the top of the straw to seal it.
STEP 2
Roll the modeling clay out into a log and wrap it around the bottom of the straw, leaving the bottom open. This is your diver.
STEP 3
Now attempt to balance the diver so that it stays upright.
STEP 4
Place the diver vertically in the drinking glass. Add or remove weight from the base or top so that when you push it down, it just about bobs back up to the surface (and stays upright).
STEP 5
Once you are happy, place the completed diver in the two liter bottle filled to the top with water. Screw on the lid. Squeeze the bottle, and the diver will drop down to the bottom of the bottle. Release it and it floats back to the surface.
