Why do some objects float and others don't?

Clay

A bowl with water

Various other things

1. Fill the bowl with water.

 2. Use clay to make a ball and put it in water

 3.Use clay to make a boat and put it also in water.

 4. Add various objects on the boat.

 

The ball is going down.

The boat floats.

If we put various objects in water, they will float.

Boat is concave and contains air. Since the displaced water weighs more than the tray, it floats. If the bowl exceeds the weight of water displaced, it sinks. Ships, even if they are made of iron, not sink, because there are areas of air inside them.