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

• Buoyancy - when in water, the density of the materials in the diver's body and in the diver's equipment determine whether the diver floats or sinks
• Boyle's law - as pressure increases the volume of gases in the diver's body and equipment decreases
• Dalton's law - in mixtures of breathing gases the concentration of the individual components of the gas mix is measured by partial pressure
• Henry's law - as pressure increases the quantity of gas adsorbed by the tissues of the human body increases, increasing the risk of decompression sickness

Physical effects of water or the underwater environment:

• Pressure - the overall pressure on a diver is the sum of the atmospheric pressure and the water pressure
• Density - common materials found in body and in the diver's equipment such as air, water, steel and lead have widely differing densities.
• Increase thermal conductivity in water, compared to air
• Absorption of light and loss of colour underwater
• Under pressure, gases compress but liquids do not
• gravitational forces and the rotation of the earth cause tidal currents
• Effects of weather such as wind, which causes waves, and temperature.