How do heavy things float?

We decided that only light things float, but then we thought about boats. How do they float?

To investigate we made our own boats out of play dough and changed the shape to see if certain shapes helped it to float. We found that if we made the play dough into a curved shape, it floated but a big lump of play dough sank. We found out that this was because of air. If you add air into a material it is more likely to float than a dense material with no air it in. Changing the shape of the play dough to a curved boat shape allowed more air into the material so it floated!

Here are some pictures of us investigating: