Diving Physics - Physical Effects of Water For Divers

Physical Effects of Water For Divers

The physical effects of water or the underwater environment are:

• Pressure - the overall pressure on a diver is the sum of the atmospheric pressure and the water pressure.
• Density - of the water, the diver's body and equipment determines the diver's buoyancy and the use of buoyant equipment.

Divers use high density materials such as lead for diving weighting systems and low density materials such as air in buoyancy compensators and lifting bags.

• Thermal conductivity of water is higher than that of air.

As water conducts heat 20 times more than air, divers in cold water must insulate their bodies with diving suits to avoid hypothermia. Gases used in diving have very different thermal conductivity; trimix conducts heat more than air and argon conducts less heat than air hence the reason many trimix divers inflate their drysuits with argon.

• Absorption of light and loss of colour underwater.

The red end of the spectrum of light is absorbed even in shallow water. Divers use artificial light underwater to reveal these absorbed colours. In deeper water no light from the surface penetrates.

• Under pressure, gases are compressible but liquids are not.

Air spaces in the diver's body and gas held in flexible equipment shrink as the diver descends and expand as the diver ascends.

• The absolute (dynamic) viscosity of water is higher (order of 100 times) than that of air. This increases the drag on an object moving through water, and it requires more effort for propulsion in water relative to the speed of movement.