Many people have a misconception that it is the ‘air in our lungs’ that keeps us buoyant. It is the change of volume of our lungs that determines whether we are positively, negatively or naturally buoyant. We can conclude that a ‘floating body’ displaces its own weight of water. The volume of water displaced by a floating body is also known as upthrust acting on the body. ‘A body wholly or partly immersed in a liquid appears to suffer a loss of weight equal to the weight of the liquid displaced’ This decrease in volume of our lungs has an influence on our buoyancy and in comes Archimedes Principle Archimedes Principle As we noted before, the greatest change in pressure happens in the first ten metres (by 50%) so it’s very important to constantly equalise these air spaces as injury can occur! This has an almost immediate effect and the first thing we’ll need to do is equalise to compensate the pressure.
The first place we feel the change in pressure is on our ears and sinus. When freediving, the 4 air spaces that need to be equalised are the mask, ears, sinus and lungs. All this means is that the product of the two variables (in this case pressure and volume) should always be equal to the same number – in this case 1. As pressure increases, volume decreases and vice versa. This is basically saying that an increase or decrease in pressure will have a direct and opposite effect on the volume. ‘As long as the temperature remains constant, the volume of a gas is inversely proportional to the absolute pressure’. For every 10 metres that we descend the pressure increases by 1 bar, therefore exerting another 1 bar of pressure on the body’s air spaces – and this is where Boyle’s law comes in to play. It’s very important that in freediving we learn to deal with this pressure slowly, have an understanding of what is happening to our body’s physiology and have an adaptive mentality towards depth.Īs you can see from the table, at surface level we have 1 bar – usually called atmospheric pressure. This pressure is far greater than the one acting on our bodies in our day to day lives because water is a lot denser than air. In fact it’s the first 10 metres which has the greatest change in pressure – take a look at the table below. This article is going to cover a few topics in physics what happens to our body during a freedive as we descend/ascend and how it effects our diving.Īs you start descending to only just a few meters, pressure immediately starts acting on our body. If you do have any question please contact me in the form on the homepage. Below is a simple explantation on what happens with a few diagrams to illustrate. Sometimes, when advancing in free-diving the physics can be a little daunting – especially for those who find physics a little challenging.
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