BASIC DIVING PHYSICS Flashcards
Pressure in diving is the result of what two factors?
- Weight of the water (hydrostatic pressure)
- Weight of the atmosphere over water (atmospheric pressure)
Forces affecting any diver at any depth must be in __________ with the force at that depth.
Pressure balance
The body can only function correctly when the pressure difference in and outside the body is very ______.
Small
Atmospheric pressure is usually expressed as _____ pounds per square inch (psi) or ____ atmosphere absolute (__ ata) at sea level.
- 14.7 psi
- 1 atmosphere absolute (1 ata)
What indicates the difference between atmospheric pressure and the pressure being measured, the reading you actually see on a gauge?
Guage pressure
What is the pressure surrounding the diver at all times?
Ambient pressure
What is the total pressure being exerted?
I.e. gauge plus atmospheric pressure
Absolute pressure
What is the weight of the atmosphere (Atmospheric pressure) at sea level?
14.7 psi
What is the weight of the water (hydrostatic pressure) measured in?
Pounds per square inch gauge (psig)
What is the formula for psig? (Pounds per square inch gauge)
Depth in feet of saltwater (fsw)
(Fsw) x .445= psig
(Round up to the next whole number)
Ex. 33 fsw
33 x .445 = 14.68 = 15 psig
What is the equation for absolute pressure (ata)?
(D + 33)/ 33 = ata
D=depth in feet of saltwater=fsw
What is the psig to ata formula?
(Psig + 14.7)/ 14.7 =ata
What is buoyancy?
The force that makes an object float.
What is 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.
What is Archimedes principle used for, and how do you find buoyancy?
Used to determine if an object or body will be negative, positive, or neutral when immersed in water. Buoyancy is weight displaced minus weight of object.
What are natural factors that affect a divers buoyancy?
- Air in lungs
- Bone structure
- Obesity/Leanness
What factors can a diver change to adjust buoyancy?
- add or remove weight
- put air in buoyancy compensator/life vest
- put air in dry suit
- put air in lungs
- vary thickness of wetsuit
What is the equation for buoyancy?
Displaced liquid weight - submerged body weight = the buoyant force
What are the water weights for fresh and saltwater?
Salt: 64 lbs/cubic foot
Fresh: 62.4 lbs/cubic foot
Oxygen (O2)
- ____% in air
- metabolized by ____
- the only gas that the body actually uses
- breathing 100% O2 under pressure can be toxic at partial pressures of ___ to ___ ata
- 21% in air
- metabolized by the body
- 1.3 to 1.6 ata
Partial Pressure
In a mixture of gases, each gas contributes to the total pressure of the mixture. This contribution is the partial pressure. The partial pressure is the pressure of the gas if the gas were in the same volume and temperature by itself.
Nitrogen (N2)
- ___% in air
- used to dilute ___ (essentially a carrier for___)
- Inert gas
- the body does not metabolize
- dissolves in the tissues
- 79% in air
- used to dilute O2 (O2)
What is an inert gas?
One that the body does not use or metabolize.
What disorder can result from breathing nitrogen under pressure? (Creating anesthetic-like properties)
At what depths does this occur?
- Nitrogen narcosis
- Usually begins at depths deeper than 100 fsw
Carbon Dioxide (CO2)
- by-product of ______ or metabolized O2 in the body
- Can be extremely toxic when breathed at _________ or ________
- respiration
- high partial pressures (PP) or high concentrations
What are the concerns involved with CO2 in diving?
- control of the quantity in the breathing supply
- removal of the exhaust after breathing
- produced by incomplete combustion of fuels
- can contaminate the diver’s air supply by placing the compressed air intake too close to the exhaust of an engine
- seriously inhibits normal bodily function
Carbon Monoxide (CO)
Humidity/Condensation
-moisture in the air/gas
-moistens body tissue, aiding diver
comfort.
-condensation can freeze and block air passages, fog diver’s faceplate, and corrode equipment
Boyle’s Law
States that at constant temperature, the absolute pressure and the volume of gas are inversely proportional.
How does Boyle’s law relate to diving? (SPAM)
- Squeeze
- Pulmonary Over Inflation Syndromes (POIS)
- Air consumption (standard cubic feet (scf) to actual cubic feet (acf): 12 scf to get 6 acf at 33 fsw)
- Minimum Manifold Pressure (MMP)
Define Minimum Manifold Pressure (MMP)
The supply pressure that will ensure that the gas supply will be delivered at a sufficient pressure to overcome the ambient seawater pressure and allow the equipment to supply the required amount of air to ventilate the rig being used.
Charles/Gay-Lussac’s Law
States that at a constant pressure, the volume of a gas is directly proportional to the change in the absolute temperature.
How does the Charles/Gay-Lussac law relate to diving? (CAR)
- Charging rates
- Air in stowage
- Recompression chamber ops
What is Dalton’s Law? (The law of partial pressure (pp))
Dalton’s law states that the total pressure exerted by a mixture of gases is equal to the sum of the pressures of each of the different gases making up the mixture, with each gas acting as if it alone was present and occupied the total volume.
The ____ is equal to the ____ of its parts.
Whole
Sum
What is the ppO2 in ata’s while breathing standard air at a depth of 60 fsw?
0.59 ata
(60+33)/33= 2.8181818181…
2.81 x .21 (% of O2 in standard air)= 0.59 ata
What two forms of gas toxicity at depth relate to Dalton’s Law?
Nitrogen narcosis
O2 toxicity
What is Henry’s Law? (Law of absorption)
The amount of any given gas that will dissolve in a liquid at a given temperature is directly proportional to the partial pressure of that gas.
What about our body, specifically in relation to our tissues, makes it so that as a diver descends deeper, more gas dissolves in the body tissues, and on ascent, the dissolved gas must be released? What law states this?
- A large percentage of the body is made up of water
- Henry’s Law
What about gases increases during the descent of a dive, causing gases to be absorbed by the tissues of the body?
Partial pressure
What controls the rate of release of inert gases during the ascent of a dive?
Ascent rates
Decompression stops
What factors affect gas absorption, and how?
Depth- the deeper the depth, the higher pp of gas
Time at depth- the longer you spend at that depth the more you will on-gas
Condition of body to off gas- (temp, work load, diver physical condition)
What are the variables associated with the condition of the body to off-gas, and how do they affect the off-gas process?
Temperature- the solubility of a gas is affected by temperature, the lower the temperature the higher the solubility.
Work load- as the body cools it will cause vasoconstriction and inhibit proper off-gassing.
Divers physical condition- fatty tissues hold more inert gas and take longer to off-gas than watery tissues.
Inert gas is ___ times more soluble in fat than in water.
5
What is gas diffusion?
The process of intermingling or mixing gas molecules.
True/False:
If two gases are placed together in a container, they will eventually mix completely regardless of the difference in weight.
True
The amount of an individual gas that will pass through a permeable membrane depends upon the ___________ of the gas on both sides of the membrane.
Partial pressure
If the pp of a gas is higher on one side of a membrane than the other, then the gas molecules will diffuse through the membrane to what side, and until what?
Diffuse to the lower pp side until the pp is equalized.
Inert gas is absorbed during descent and on the bottom (on-gassing) due to the increase in ____________.
Partial pressure (pp)
Inert gas is eliminated during ______ (off-gassing) because the ____ decreases.
Ascent Partial pressure (pp)
What are three types of energy encountered in diving?
Light
Mechanical (Sound)
Heat
Light travels ______ in air than in water.
Faster
Light is affected by what (4) factors underwater?
Salinity
Turbidity
Size of particles in water
Pollution
What is the order of colors that you lose first as depth increases underwater?
ROYGBIV
Colder water is ______ than warm water.
Denser
Why does sound travel farther and faster under water?
Because water is more dense than air.
Sound is ___ times faster in water than in air.
4 (ex. Sonar)
What term describes temperature changes in layers of large bodies of water?
Thermocline
Water is a much ______ conductor of heat than air.
Better
At what water temp will a diver lose heat to the water faster than his body can replace it (without protection)?
80 degrees F
Body heat is lost ___ times faster in water.
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