Now that summer has arrived, the boats begin to populate the Spanish beaches. There are many types of boats, but they all have one thing in common: they float. Something that seems so obvious and simple that we have never questioned why ships must fulfill that function, float so as not to sink. But why do ships float?
The boats are able to float in the sea or in river water by a physical law known as Archimedes’ Principle. This law comes to say that there is a force that pushes the boat from the bottom up thanks to a design based on this own law.
We must be clear that ships are denser than the water itself and occupy a large volume, despite being made mostly of metal.
And what is density? Density is the amount of matter that exists per unit volume. This means that, if we make 1 cubic meter of iron, by itself and its density, it will sink into the sea. Now, if we build this same cubic meter with a hollow sphere, its dense volume will be greater than the solid sphere, therefore, the water will push it upwards.
Demonstration of Archimedes
From a very young age, Archimedes grew up in a family environment conducive to the study of science. His father, an astronomer, started his son in science and soon showed a great predisposition for it.
Archimedes’ Principle was demonstrated while Archimedes himself took a bath. There he discovered that the water level in the bathtub rose as his body entered the water. The explanation meant that every body immersed in a fluid experiences a vertical and upward thrust equal to the weight of the dislodged fluid.
This explanation consists of two parts: the study of the forces on a portion of fluid in equilibrium with the rest of the fluid; and a second part where said portion is replaced by a solid body of the same shape and dimensions.
Therefore, although ships are made of materials much denser than water, the density of the ship itself is its total weight divided by the external volume of the hull. This means that the hull must have an outer volume large enough to give the boat a density slightly lower than that of the water where it is submerged. That is why so much of a ship is air.
For this reason, shipbuilding engineers rely on Archimedes’ Principle to make ships since ancient times.
