The Diver Experiment

We did this fun experiment in school to-day!
We had to figure out how to get the diver (on the end of the paper clip) to go to the bottom of the bottle and back up to the top.
We tried lots of ideas - shaking it around, shaking it up and down, rolling it across the classroom, turning it upside down - but even though the diver went down, he wouldn't come back up. We had to rescue him a lot :)

In the end we saw that if you simply squeeze the bottle the diver will fall to the bottom. When you let go he floats up to the top again. This is because there is air in the pen cap and air is lighter than water so it floats! But when we squeeze the bottle it causes water up into the pen cap, it gets heavier and sinks to the bottom !