The ancient Greek scientist Archimedes was the first to discover the principle of buoyancy. He observed that an object immersed in a fluid (water in the case of divers) would be pushed up by a force equal to the weight of the fluid it displaced. In other words, buoyancy is of significant importance to you as a diver because you will witness its effects whenever you dive.
Buoyance is broken down into three types.
When an object weighs less than the weight of the water it displaces, this generally means the object will float on the surface. If the object were held underwater and if it were to be released, it would head straight for the surface.
Divers achieve positive buoyancy by inflating their buoyancy control devices (BCDs) while on the surface to keep them floating, and they save energy because they do not need to swim to keep afloat.
The diver’s goal while underwater is to neither sink nor float. So, according to the rules of buoyancy, the amount of water displaced is equal to the combined weight of the diver and the equipment used. Neutral buoyancy—holding position in the water column without moving your arms or feet—is important when you swim over a reef because you do not want to touch or damage marine organisms, such as corals. Neutral buoyancy also prevents you from crashing into the bottom, especially important if the bottom is silty. Imagine the mess that can make. And being neutral will allow you to complete your safety stop at a fixed depth.
This feeling of weightlessness and the sensation of flying through the water in complete control is a fun part of the dive experience. This skill takes some time to master but is well worth the effort.
This is when the object sinks. The weight of the object is more than the weight of water it displaces. A diver achieves this by deflating the BCD and sinking.