Why do things float or sink?

We have just completed an experiment investigating why things float or sink. Students filled film canisters with various weights. The students found the mass when the film canister sunk, floated, and was at neutral buoyancy. They used water displacement to find the volume of the film canister. Here's the data from 15 of the groups.


Averaging the data we got a mean mass for the sinking items as 50.6. For floating items it was 16.8. For neutral items the mass was 40.5. The average volume we found was 40.2

Students then created a rule based on the data. It appeared that the objects where their mass was greater than their volume, they would float. If the mass was less, it would sink. If it was the same, it would be neutral.

The relationship between mass and volume is called density. It is the key topic we will be studying for the next two weeks.