Question: How do heavy ships float?

Mark Burnley answered on 18 Jun 2011:

The size of a ship is often measured in terms of “displacement”. Submerging something in water results in a “hole” in the water, and the water tries to fill the hole, which creates a force all around the object you have submerged. However, because the pressure of the water increases with depth, the force is greatest at the bottom of the object and so the overall effect is to push the object up. If this force (called bouyancy) is bigger than the force of gravity (that is, the weight of the object), then the object floats. So, provided a ship displaces enough water, the bouyant force will be greater than the gravitational force and it will float, even if it weighs thousands of tons. Humans usually displace a bit more water than their weight, and this is why it is (only just) possible to float with your head above water.