Ancient Greek scientist Archimedes was the first to discover the principle of buoyancy. He observed that an object immersed in water would be pushed up by a force equal to the weight of the fluid it displaced. In other words, the object had the ability to float in water. The principle of buoyancy is of significant importance to divers because they apply it whenever they dive. Divers break this down into three types of buoyancy.
The object displaces more water than it weighs. Generally, this would mean the object is floating on the surface. If the object were held underwater and if it were to be released, it would head straight for the surface. Divers use this positive buoyancy by inflating their buoyancy compensation devices (BCDs) while on the surface to keep them floating, saving energy by not fighting to keep afloat.
The diver’s goal while underwater is to neither sink nor float. The amount of water displaced is equal to the body weight and the equipment used. Neutral buoyancy is important for swimming over a reef without touching or damaging corals and for the ability to hold a depth at 5 meters/15 feet while completing a safety stop. This feeling of weightlessness is a fun part of the dive experience. This skill takes some time to master.
This is when the object sinks. The weight of the object is more than the water displaced by it. The diver can achieve this by deflating the BCD and sinking.