Diving Physics - Laws of Physics For Diving

Laws of Physics For Diving

The main laws of physics that govern the physics of the SCUBA diver and of diving equipment are:

• Archimedes' Principle (Buoyancy) - Ignoring the minor effect of surface tensions, an object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object. Thus, when in water (a fluid), the weight of the volume of water displaced as compared to the weight of the materials in the diver's body and in the diver's equipment, determine whether the diver floats or sinks.

Buoyancy control, and being able to maintain neutral buoyancy in particular, is an important safety skill. The diver needs to understand buoyancy to be able to effectively and safely operate drysuits, buoyancy compensators, diving weighting systems and lifting bags.

• Boyle's law - as pressure changes, the volume of gases in the diver's body and soft equipment changes too.

The volume of air in a non-rigid container (such as a diver's lungs or buoyancy compensation device), decreases as external pressure increases while the diver descends in the water. Likewise, the volume of air in such non-rigid containers increases on the ascent. Changes in the volume of gases in the diver and the diver's equipment affect buoyancy. This creates a positive feedback loop on both ascent and descent.

The quantity of open circuit gas breathed by a diver increases with pressure and depth.

• Gay-Lussac's second law – as temperature increases the pressure in a diving cylinder increases (originally described by Guillaume Amontons).

This is why a diver who enters cold water with a warm diving cylinder, for instance after a recent quick fill, finds the gas pressure of the cylinder drops by an unexpectedly large amount.

• Dalton's law - in mixtures of breathing gases the concentration of the individual components of the gas mix is measured by partial pressure

Partial pressure is a useful measure for expressing limits for avoiding nitrogen narcosis and oxygen toxicity.

• Henry's law - as pressure increases the quantity of gas adsorbed by the tissues of the human body increases.

This helps explain nitrogen narcosis, oxygen toxicity and decompression sickness.

• Snell's law - the index of refraction of water is similar to that of the cornea of the eye—30% greater than air.

This is the reason a diver cannot see clearly underwater without a diving mask with an internal airspace.