Method:

What you have to do:: 1) Our pen cap had a hole at the top, so we had too plug this with some white tack.

2) Stick some white tack for weight on to the pointy end of the pen cap.

3) Make sure that the plastic bottle is filled to the very top with water and that the 'diver' just floats.

4) Put on the bottle cap and squeeze the bottle hard.

5) Observe.

Result: When you squeeze the bottle, you should find that the 'diver' sinks to the bottom of the bottle. When you release the bottle, the 'diver' floats back to the top.

Conclusion: Air is trapped in the lid of the pen, so when you put pressure on the bottle, you force water into the biro lid. This compresses the air, and the extra water makes the 'diver' or pen lid heavier - it sinks. Let go of the bottle and the lid floats again.

Sixth Class Experiments