Subject 4 articles
Scuba Diving Physics
Scuba diving physics is the reason every rule in diving exists. Pressure, gas volume, buoyancy and light all behave differently underwater, and each one shapes how you breathe, float, see and plan a dive.
Articles in scuba diving physics
- Archimedes' Principle in Diving
The physics of floating: displacement, salt versus fresh water and changing buoyancy.
- Boyle's Law in Scuba Diving
Why gas shrinks on descent, expands on ascent, and why you never hold your breath.
- Light and Color Underwater
Color loss with depth, magnification at the mask and how sound travels underwater.
- Water Pressure at Depth
How fast pressure rises underwater, and absolute versus gauge pressure.
Why physics matters to divers
On land you live under one atmosphere of air pressure and rarely think about it. Underwater, the weight of the water above you adds pressure quickly: every 10 metres (33 feet) of seawater adds as much again as the whole atmosphere. That one fact explains most of what you learn in a dive course, from why you never hold your breath to why your air runs out faster on a deep dive.
The articles in this subject cover the four ideas that matter most. Water pressure at depth explains how pressure is measured and how fast it grows. Boyle's law shows what that pressure does to the air in your lungs, mask, ears and buoyancy device. Archimedes' principle explains why you float, sink or hover. Light and color underwater covers why reds vanish, why fish look closer than they are and why sound seems to come from everywhere.
How the subjects connect
Physics leads straight into the rest of this wiki. Gas absorbed under pressure is the cause of decompression sickness and nitrogen narcosis. The pressure of oxygen in a gas mix sets the depth limits of enriched air nitrox. Buoyancy physics is what you practise when you learn neutral buoyancy. If you understand the physics, the safety rules stop being a list to memorise and start making sense.
Units used in this wiki
Divers use both metric and imperial units, so this wiki gives both. Depth is in metres and feet (1 m is about 3.3 ft). Pressure is in bar and pounds per square inch (1 bar is about 14.5 psi), and an atmosphere (atm) is close enough to 1 bar for dive planning. "Absolute" pressure includes the atmosphere above the water; "gauge" pressure counts only the water. When this wiki says a depth is "3 bar", it means absolute pressure unless it says otherwise.
A quick summary
- Pressure rises by about 1 bar for every 10 m (33 ft) of seawater, and slightly less in fresh water.
- Gas volume shrinks as pressure rises and expands as it falls, with the biggest relative change near the surface.
- You float when you displace more water than you weigh, and the balance changes as your suit compresses and your tank empties.
- Water filters out red light first, bends light at your mask and carries sound about four times faster than air.
These are general explanations for curious divers and students. They support training from a certified instructor; they don't replace it.