Video: Submarine

In 1775, the American David Bushnell invented one of the first submarines. Because of its unusual shape, it was baptized “the turtle”.

Just like any modern-day submarine, the turtle operates thanks to ballast … and a propeller

A submarine is a perfect application of Archimedes’ principle of buoyancy.

«  Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object”

This new force is known as buoyant force. It depends on the immersed volume.

There is another force that we all know: weight.

If the downward weight is greater than the upward buoyant force, the object sinks.

A compact mass displaces very little water whereas a ship, given its shape, displaces a lot of water

When the buoyant force is equal to the weight, the ship floats.

Floating or sinking is just a question of balance between these two opposing forces : weight and buoyant force.

A submarine is designed to be able to modify its own weight. That is the role of the ballast tanks.

They are big tanks which fill up with water to weigh down the ship…

Or fill up with air to make it lighter.

When diving, the submarine balances both forces equally.

It can then move around and adjust its depth by moving the diving plane.

There are over 500 submarines in use today in the world, primarily for military use. Like the Buschnell turtle…