Buoyancy changes with depth. During a descent, as ambient pressure increases, the air in your body compresses in particular in your lungs, and you slowly become less buoyant.
There are three types of buoyancy. At the surface, you are positively buoyant i.e. the buoyant force exceeds your weight. As you descend, you slowly become neutrally buoyant. If you descend further, you become negatively buoyant i.e. your weight exceeds the buoyant force. As negative buoyancy increases with depth during a freedive, a point is reached where gravity overcomes the buoyancy of your body and you enter a state called free fall. When this happens, you can stop finning and allow yourself to fall effortlessly.
Your buoyancy depends upon the composition of your body. Fatty tissues are positively buoyant in water, whereas muscles are negatively buoyant. The proportions of these different tissues in your body affect your buoyancy in the water and determine your personal weighting requirements. To note, your weighting can be very different from your buddy.
Photo: Sandy Orka
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