While people may think that the physics behind scuba diving is pretty simple, with just a steady supply of oxygen all that is necessary to breath underwater, this is not at all the case. When diving deep underwater, several factors must be accounted for in order for the diver to make a safe journey down and back. The most important of these are the gas laws. Water has different characteristics than air, so gases will tend act differently as well. Water, unlike air, is uncompressible, and also happens to be denser than air. In order to account for these differences, divers make use of several gas laws to insure their safety.
The first of these is Boyle’s Law, which relates the volume and pressure of a gas at held at a constant temperature. The equation for Boyle’s Law looks like this:
PV = k
Where P=pressure of gas, V=volume of gas, and k is a constant. Basically, Boyle’s Law states that when you increase the pressure on a gas, the volume decreases, and visa versa. As a diver descends, the pressure of the water on himself and the oxygen he is breathing increasing, decreasing the total volume. The opposite holds for while he is coming up. This is why it is important to breathe out as you are rising, so your lungs to not over-inflate. Here’s a video demonstrating Boyle’s Law as it relates to scuba diving.
Another important gas law when looking at scuba diving is Henry’s Law, which states that the mass of a gas that dissolves in a volume of liquid is proportional to the pressure of the gas. The equation goes as follows:
P = KC
Where P=partial pressure of gas, C=concentration of gas, and K= Henry’s Law constant. This law is important to divers because it means that at a higher pressure, a diver’s body will absorb more gasses. This law relates to decompression sickness, when a diver swims deep and then rises too quickly, causes gas bubbles to form in the tissue. A video showing Henry’s Law as it relates to scuba diving can be found here: