When a boat floats in the water, there is a very important principle involved. It called the Archimedes' principle .It is named after a famous mathematician who lived over 2,000 years ago. This principle states that when an object is placed into water (or any other liquid), there is an automatic change. The object put into the water must remove an amount of liquid equal the object's weight.When a 1,000 kilograms boat is put into water. It will move more than 1,000 kilograms of water around it. The boat floats because it displaces more water than the actual boat weight. But how do we know if an object will float or sink?