272 NAUI Master Scuba Diver GLOSSARY Glossary A Absolute pressure: The total pressure, including atmospheric and hydrostatic pressures, exerted at any point. Absolute zero: The lowest temperature that could possibly be reached (-273° C or -459.72° F). Absorption: The taking up of nitrogen in tissues. Algae: Non-flowering aquatic plants. Altitude dive: One that is conducted at an altitude greater than 305 m (1,000 ft). Ambient pressure: The pressure of the fluid surrounding an object. Amonton’s Law: For any gas at a constant volume, the pressure of the gas will vary directly with the absolute temperature. Analog depth gauge: An instrument with hands that point to numbers as a direct result of mechanical force. Angle of attack: The angle between a diver’s longitudinal axis and his or her trim. Anoxia: Lacking oxygen. Anxiety: Fear or apprehension which one experiences in the face of real or imagined danger. Archimedes Principle: Any object wholly or partly immersed in a fluid is buoyed up by a force equal to the weight of the fluid displaced by the object. Asphyxiate: Impairing or ceasing breathing that can lead to death from a lack of oxygen and excessive carbon dioxide in the blood. B Backrush: The return flow of water from waves rushing onto a shore. Sometimes mistakenly referred to as “undertow.” Balanced valve: A valve that controls pressure in such a way that the pressure does not affect the force needed to open and close the valve. Bearing: The angular direction to an object expressed in terms of compass degrees from north, e.g., a bearing of 270°. Benthic: Pertaining to life found in or at the bottom of the oceans. Bends: See Decompression Sickness. Bezel: A rotating ring on a compass or watch that can be set as a reference. Bloom: A condition of poor visibility resulting from excessive algae or plankton. Bottom timer: A device which automatically records a diver’s bottom time. Bourdon movement gauge: An instrument that uses a curved metal tube as a pressure detector. Boyle’s Law: For any gas at a constant temperature, the volume will vary inversely with the absolute pressure while the density will vary directly with the absolute pressure. Buoyancy: The upward force exerted on an immersed or floating body by a fluid. Buoyant ascent: Emergency ascent made by dropping weight belt or retaining expanding air in the BC. Burst disc: A thin metal disc found in cylinder valves as a safety feature and designed to rupture and relieve excessive pressure in a cylinder. C Capillary depth gauge: An instrument that indicates depth via the compression of air in a transparent tube. Ceiling: A depth indicated by a dive computer above which one may not safely ascend.
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