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"Under Pressure" Experiments

Air Pressure 2 - "The Cartesian Diver"

Experiment: To make a Cartesian Diver

Materials:

You will need:

Clear 1 ¹/₂  - 2 litre bottle.
Small clear plastic cup
About 6 cm of plastic tube (available from aquarium shops)
Water
Ketchup Sachet
Paper clips
Elastic Band

Method:

What you have to do: 

1) Fill up your bottle with water - almost to the top.

2) Fold your tube in half and tie the two ends together tightly with the elastic band.

3) Attach about 2-3 paper clips to the elastic band on the tube.

4) Drop your tube (diver) into the bottle. It should be a tiny bit above the surface of the water. If too heavy or too light, adjust the number of paper clips.

5) Screw the lid tightly on the bottle and then squeeze the sides of the bottle and see what happens.

6) Do the same thing with the ketchup sachet - don't puncture it - just add weight by attaching paper clips.

Result: When you squeeze the bottle, the diver (or ketchup sachet) sinks to the bottom and when you let go, it floats back up to the surface.

Conclusion: Squeezing the bottle forces water into the tube (diver), which adds more weight and causes it to sink.

If you use a ketchup sachet, squeezing the bottle compresses the air in the sachet. The air takes up less space and therefore the weight of the ketchup pulls the sachet down.

Sixth Class Experiments