Key Stage 3 Scientists Create Cartesian Divers

This week saw Key Stage 3 Virtual Science Club students creating cartesian divers in a bottle, using sachets of sauce as the diver - squash the bottle and the diver sinks, release the bottle and the diver floats. 

Dillan 7D tried this experiment:

"At first, I tried to put the mayonnaise sachet in the bottle with some Blu tack, but it didn't work properly, even though it floated. I then added some more Blu tack onto the sachet and it seemed to float in the bottle. When I squeezed the bottle, the sachet dived down. I tried the same amount of water and the same amount of Blu tack for the ketchup and the brown sauce sachets. However, for those it didn't work.  I changed the amount of water to a half, and none of the sachets behaved like submarines. I also tried a water balloon instead of a sachet and that didn't work either."

If you would like to have a go at creating cartesian divers, please watch this YouTube video for instructions:

https://www.youtube.com/watch?v=OM6iC6N12xY 

Why it happens: it is the air in the ketchup sachet (water does not compress, but air does). When the air is compressed (by squeezing the bottle), it becomes denser than the water, causing the sachet to sink. When you release the bottle, the air molecules spread out again and the pack will float to the top.

It is great to see our Key Stage 3 scientists undertaking the basic experiment and developing their ideas.

Dr Thomassen, Science