For example, as the temperature then the appropriate term is weight. If direc- lowers during a humid evening, the dew point tion is not a factor, as in a gas law problem, is reached and fog forms. As long as the then mass is the proper term.
Epub Bove And Davis Diving Medicine Fourth Edition
VOLUME With diving, it is desirable to have the humidity of the breathing gas as low as pos- Volume is the term used to describe capac- sible to prevent the formation of ice within ity. It is measured in units of length cubed.
If the humidity of the gas is high, urement system during the entire calcula- then water vapor can condense and freeze. It tion. For example, the formula relating depth is possible to freeze the regulator in either an in feet and pressure in atmospheres: open or a shut position. Because demand regulator. When one is diving gauges calibrated in standards other than in extreme cold conditions, it is best not to feet in seawater one major American manu- exhale through a regulator until after it is facturer has a series of depth gauges cali- beneath the surface of the water and allowed brated in feet of fresh water , or in locations to equilibrate to ambient temperature.
Air is a mixture of gases that primarily includes nitrogen and oxygen. It also con- Water tains water vapor, varying concentrations of trace gases e. The amount carbon dioxide, industrial pollutants, hydro- of water that air can hold is proportional to carbons and nitrous oxides from internal the temperature; the higher the temperature, combustion engines, and particulate matter the more water vapor the air can hold.
The Table 2—3. The amount of water vapor present Table 2—3. Typical Concentration divided by the maximum possible water of Dry Air vapor concentration at a given temperature is called the relative humidity. Another mea- Nitrogen Density, particularly of liquids and gases, changes with temperature.
Relation of buoyancy upward arrows to gravity is a ratio and has no units. The against the force of weight. This Archimedes, the Greek mathematician, scheme allows for no positive or negative. Objects these factors can be used to determine the that sink are frequently called negatively third. This is best illustrated by example: buoyant.
Objects that remain station- ary at depth are said to be neutrally buoyant. Buoyancy is best understood by the appli- cation of force vectors. Vectors are mathe- matical constructs that have magnitude What is the buoyancy in seawater of a and direction. Determine forces involved: Determine forces involved: a. To sink, the object would have to weigh more than an additional lb without changing volume. A fully geared diver in a wet suit weighs Although the object is buoyant i.
In fresh water, this diver with a force of lb is pushing up on this log , scuba cylinder containing psig needs it will not be completely out of the water. How much lead will The density of the log can then be used this diver need when diving in a wet suit to determine how much of the log will be in seawater? The amount of the volume that is submerged will be deter- To hover, the volume of water dis- mined by the ratio between the density placed by the diver must exert a buoyant of the log and the density of the seawa- force upward equal to the total weight of ter.
In general: the diver plus gear downward force.
Density of liquid. This diver displaces a volume of 3. When moving from seawater to less dense fresh water, divers should remove weight. A fully geared diver in a wet suit weighs lb. In seawater, this diver needs 18 lb Divers wearing wet or dry suits have an of lead to hover. How much lead will this additional factor to consider. Within the wet diver need when diving in a wet suit in suit are trapped bubbles of gas; a dry suit fresh water?
As a diver descends, the volume To hover, the volume of water dis- decreases as ambient pressure increases, placed by the diver must exert an less water is displaced, and the diver upward buoyant force equal to the total becomes less buoyant and sinks. On ascent, weight of the diver plus gear downward the gas expands and occupies a larger force. This is the upward buoyant force volume, more water is displaced, and the exerted by the displaced volume of sea- buoyant upward force increases.
Apply force arrows: Lift a lb anchor from the bottom of a lake bed. Energy vents. How many 55 gal drums will it take that can be derived by a future change in to lift the anchor? Determine forces involved: Consider a pile driver. This giant hammer device utilizes the kinetic energy of a large Determine weight of water displaced: mass to drive construction supports into the earth. Here, while motionless, it possesses only potential energy.
During the entire movement, the large falling mass has 0. This is known as the Conservation of Energy princi- ple. Energy can be changed in form, however. The kinetic energy of the falling water cient to lift the lb anchor. In practice, turns a turbine mechanical energy that large lifting objects like a 55 gal drum have drives a generator, producing electricity a large surface area and generate consider- electric energy.
The electricity lights a light able drag, which decreases lifting capacity. Weight is the diver is subject to a number of forces. In the most commonly encountered force. It has a vertical plane, gravity weight tends to magnitude how much push and a direction make the diver descend and buoyancy from too little weight or too much air in the buoy- ancy compensator makes the diver ascend.
In the horizontal plane, the diver moves Table 2—4. The Six Forms of Energy forward, propelled by the force of the kick. The thrust, or forward motion, must over- Mechanical The sum of potential and kinetic come drag or friction that the diver and energies derived from the equipment present to the water. The over- movement of a body Heat Energy derived from molecular motion weighted diver must continually expend Radiant Energy in the form of energy to overcome gravity and remain at electromagnetic waves such as constant depth, and the underweighted light, x-rays, or radio waves diver must continually expend energy in an Chemical Energy released from chemical attempt to overcome buoyancy with leg reactions Electrical Energy derived from moving electrons power.
A more horizontal position presents a Nuclear Energy derived from atomic forces smaller area to the path of movement and within the atom thus lessens resistance. A body will remain at rest or in a state of uniform motion along a straight line unless Work done acted upon by some outside force.
Force acting on a mass produces an accel- eration. It is convenient to measure the newtons, i. The amount of heat neces- then force is in dynes. If mass is in slugs sary to raise 1 g of pure water from One thousand pounds. The corre- 3.
For every action, there is an equal and sponding English measurement is the opposite reaction. One BTU is equivalent to calories. WORK Matter may be thought of as a heat reser- voir. Because of their molecular makeup, dif- Work is the application of a force over a ferent substances are capable of holding distance. Work requires energy. If no move- different amounts of heat. The amount of ment occurs, no work is accomplished. The higher the heat capacity, the more done when 1 newton of force moves an heat a substance can absorb and store.
Bove & Davis: Diving Medicine, 4th Edition
Heat capacities of gases are commonly forces of weight and buoyancy. In addition, overweighted divers gen- erally are not horizontal in the water. More drag means Argon 0. Units of work are provided in Oxygen 0.
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Chapter 2 Diving Physics This is why respira- ary to measure thermal properties of a gas at tory heat loss while one is breathing constant pressure Cp or constant volume helium is much less than would be Cv. Values for thermal properties of mater- expected solely according to heat capac- ials can be found in a number of standard ity. Respiratory heat loss at depth from references.
Gas density values 1. For dry air:. For water: of the breathing gas and environment in which the diver is operating.
Thermal conductivity is expressed as the amount of heat that can be transmitted c. Thermal The amount of heat required to raise the temperature of g of helium is larger Table 2—6. Thermal Conductivity than for an equal mass of air. However, the Air 2. Wool 8. The precise ratio depends on environment. This heat loss occurs primarily temperature, pressure, amount of particulate via direct contact with the environment matter present, and humidity of the air, as immersion in water or a heliox atmosphere well as the temperature and purity of the contained within a diving habitat.