Archimedes Principle
Some objects, when placed in water, float, while others sink, and still others neither float nor sink. This is a function of buoyancy. The idea of buoyancy was summed up by Archimedes, a Greek mathematician, in what is known as Archimedes Principle: Any object, wholly or partly immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object.
The equation for this force is:
where d is the density of the liquid, V is volume of liquid displaced and g is the gravitational acceleration (9.8 m/s2).
From this principle, we can see that whether an object floats or sinks, is based on not only its weight, but also the amount of water it displaces. That is why a very heavy ocean liner can float. It displaces a large amount of water.