Cartesian diver

Using an ignition tube and a plastic bottle you can create a simple toy that will have your friends puzzled.
Fill the bottle with water and insert the inverted ignition tube with trapped air inside it. Seal the bottle and squeeze the sides. You will see the water level inside the ignition tube rise. As the water level rises the ignition tube sinks.

You can decorate the ignition tube to make it look like a diver.
You can finely tune the cartesian diver by adjusting the amount of air in it. You can do this by feeling the tube with water and then emptying small amounts of water by flicking the tube with your fingers, as shown on the right.

 

 

A slight squeeze on the side of the bottle should set the tube sinking view the video on the right to see how this works. Squeezing the bottle compresses the air in the ignition tube but not the water. Water does not compress. Click for more information on the states of matter.
Why does water not compress but air does?
What happens to the volume of air in the diver when the pressure is increased?
When the volume of air in the diver decreases the diver will
What happens to the volume of water inside the diver when you squeeze the bottle?
Stephen's diver, when placed in the bottle, slowly sinks to the bottom. Discuss two ways that Stephen can make his diver float to the surface. Explain why.
From your observations discuss the relationship between pressure of a gas and its volume.
Activities with your diver.
Measure the distance from the top to the bottom of the bottle, allowing for the length of the diver. As quickly as possible perform ten laps. One lap is when the diver starts at the top, touches the bottom and returns to the top again. Using a stop-watch time this and calculate the average speed of the diver over the ten laps.
Fine control of the diver. On the outside of the bottle mark lines at 2cm intervals. Label the lines from 1 to 6. Take it in turns to see who has the est control of the diver.
Starting at the top the diver descends to a specified numbered line and remains there for 2 seconds. The diver then ascends or descends to the next specified line and holds for two seconds. Finally the diver ascends or descends to the last line and holds for two seconds.
How does the temperature of the water influence the control you have over the diver? Prepare your diver with warm water and test it. Place the diver in the fridge and repeat when the water is cold. Do you notice any change? Explain.
Does temperature affect the pressure needed to make your diver descend? Explain.
Modify the diver so that it can hook a small object from the bottom and bring it to the surface.
Synchronized diving- Introduce a second diver to the bottle that is slightly different. One diver should descend soon after the other with a small modification in pressure.
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