Physics Flashcards
Water conducts heat more efficiently because it is more _____ than air
Dense
What form of heat transmission most effects divers?
Conduction
Water is able to conduct heat _____ times faster than air.
20
Heat vs temperature
How can two objects of different masses have the same temperature but different amounts of heat
Which is why takes 4 times more energy to what same volume of water as it does air (if it was the same mass of volume as air it would take 3200 times more heat)
Heat is total kinetic energy
Temperature is average molecular motion within the mass
Refraction caused by light traveling from one ____ to another with different ______
Medium. Density
Underwater objects appear ____ by a ratio of ____ (actual to apparent distance)
Closer. 4:3
Underwater objects are magnified by ___%
33
Visual reversal means
Objects appear further than really are
Why does visual reversal occur
Turbidity - leading to a function of human perception because of lack of contrast, hazy objects brain interprets as further away
Light waves contain ______ while sound are compromised of _____
Electromagnetic energy. Mechanical energy
Sounds travels through objects better if they are more _____ which are typically objects that have more ______
Elasticity. Dense
Sounds travels ___ times faster in water
4
Because sound travels faster in water why do divers have difficulty determining direction
Brain can’t distinguish delay between ears or intensity difference
Archimedes principle - any object wholly or partially immersed in fluid is buoyed up by a force _____
Equal to weight of fluid displaced by object
Do you need to know the displacement of an object to calculate its buoyancy or just its weight? What about depth
Depth not matter, but do need displacement to calculate its buoyancy
Then subtract buoyancy from weight to know how more more displacement needed to lift
Specific gravity of pure water is
1.0
If something as a specific gravity of .8 in pure water will it sink or float
Float
What is the formula to figure out how much cubic feet of sea water is needed to be displaced to lift something
Weight of object - (cubic feet of displacement * 64) = Amount needed to be buoyed / 64 = cubic feet of water needed to displace to lift object
What changes in fresh water with buoyancy in regards to a cubic foot
Does depth matter
62.4lbs
No
How much water must you displace to lift an object to surface at 1,457 feet of seawater. It weighs 1000 lbs and displaces 5 cubic feet.
How many hundred pound lift bags
What if it was shallower
1000 - (5 * 64) = 680lbs needed to make buoyant / 64 = 10.625 cubic feet of water to displace to make buoyant
7 bags
Depth not matter in terms of displacement
In freshwater the car displaces 10 cubic feet but weighs 10,000lbs so how many cubic feet of water must you displace to lift it from the bottom
Over 150 cubic feet because you have to lift 9,376 lbs
10,000 - (10 * 62.4) = 9,376 / 62.4 = 150.26
For buoyancy how much does 1 cubic foot of freshwater weigh; how about salt water?
62.4 lbs 64lbs
Is there a difference between absolute and ambient pressure?
What about gauge pressure
What does 1ata equal in psi
What does 1 foot of seawater equal in psi? What if I forget how can I figure this out for seawater; what about freshwater
No
Gauge pressure counts pressure at sea level as 0lbs whereas absolute or ambient includes the 14.7lbs psi of the air
- 7psi
- 7/33 = 0.445
- 7/34 = 0.432
Absolute pressure at a depth of 300 feet seawater in psia vs psig
What is the difference
(300*0.445) +14.7 = 148.2 psia vs 133.5 psig
Psig not included air pressure as 0 at sea level
What is 1 ata of freshwater in feet vs seawater
34 for fresh 33 for sea
How else could you figure out absolute pressure at 300 ft seawater without multiplying by 0.445 psi per foot
300ft / 33 ft = 9.09 ata + 1 ata air pressure = 10.09 ata at 300 ft * 14.7lbs per ata = 148.3 psia
Ambient pressure of 130ft of seawater in psia
(130*0.445)+14.7 =72.55psia
Gauge pressure for 50 feet of seawater
50*0.445= 22.25psig
Freshwater depth of 68’ what is it in psia vs psig vs ambient pressure
68*(14.7/34) = 29.38 psig + 14.7 = 44.08 psia or ambient
A balloon containing 1 cubic foot of air released from 10 ata, if not explode how much air in balloon at surface?
What depth is 10 ata
10 cubic feet
(10 ata * 33) -33 = 297
Boyle’s law - if temperature is constant, the volume of a given mass of gas is _____ proportional to the absolute pressure.
Inversely
10 cubic foot ballon taken to 165 feet what would its volume be
(165/33) + 1 ata for air = 6 ata
10/6 = 1.67 cubic feet
A ballon with 2 cubic feet of air at 100’ seawater what is its approximate volume at 300’
Bring balloon to surface and then down
(99/33) +1 = 4 * 2 = 8 cubic feet at surface
(300/33) +1 = 10 ata
8/10 = .8 cubic feet
Balloon of 10 cubic feet at 25 feet is taken to 85 feet, what is exact volume at 85 feet
P1V1=P2V2
(250.445) + 14.7) * 10)= ((850.445) + 14.7)) * v2
- 25=52.53 * v2
- 25/52.3 = 4.92
A filled scuba cylinder at surface now taken to 66’, the air is 3 times denser? T/F
False - it’s not flexible therefore doesn’t decrease in size as depth (pressure) increases therefore air inside unaffected by increasing water pressure
How full is a gas volume in a flexible container that was full at the surface at 33’, 66’, 99’
1/2, 1/3, 1/4
Does a divers lung volume need to remain constant regardless of depth at which he breathes ? Y/N
Yes
Does the density of the air change in the lung depending on the depth he is breathing at? Y/N
Yes
To be able to breathe the external pressure must be _____ to the air we are breathing. When we breathe we must breathe a _____ breath regardless of the pressure surrounding us.
Equal
Full
Ex) try to breathe from a hose 3 ft underwater it’s super difficult
The air a diver breathes at 165’ seawater is _____ dense as the air on the surface from the same cylinder.
165/33 + 1ata= 6 ata
6
Diver breathing at 25 psig per minute at surface goes to 132’ seawater, assuming nothing else changes at what rate is he breathing per minute
132/33 + 1ata = 5ata
5*25 psig = 125 psig per minute
Consumption rate of 2 cubic feet per minute at 33’ seawater, what will rate be at 99’
33’/33’ +1 = 2ata / 2 cubic feet = 1 cubic feet per minute at surface
99’/33’ +1ata = 4 ata
4ata * 1= 4 cubic foot per minute
3 cubic feet per minute at 66’ of seawater air consumption rate, what is rate at 200’
66/33 + 1 = 3ata
3/3 = 1 cubic foot at surface
200/33 +1 =7.06 ata * 1 cubic foot at surface = 7.06 cubic feet per minute
Air consumption rate 2 cubic feet per minute at 33’ what is rate in psig per minute at 100’
33’= 2 ata 2/2= 1 cubic foot per minute at surface
However you can’t figure out the psig because you are comparing apples to oranges. Without providing a conversion from cubic feet to psig per minute you can only answer in cubic feet.
What happens to a balloon filed with 1 cubic foot of air that you put in the freezer
Balloon shrinks in volume
Charles’ law states the amount of change in volume of gas is ______ proportional to the change in the absolute temperature at a constant pressure.
Directly
If you took a scuba cylinder on an ice dive describe what would happen to the volume and pressure
Volume is unchanged but pressure decrease
An 80 cubic foot scuba cylinder is filled to 3000 psi at ambient temp of 80 degrees is then used in water temp of 40 degrees what would be the APPROXIMATE cylinder pressure
40 degree difference so multiply by 5 psi for each 1 degree
200 psi left so 2800 psi
What if the cylinder was 3225 psi and 78 degrees goes to 44 degrees what is the exact new pressure
(P1 x V1)/T1 = (P2 x V2)/T2
Don’t need V so
(P1/T1)=(P2/T2)
Must convert temp to Rankine as working in absolute terms so add 460 to Fahrenheit
Also must add and later subtract 14.7psi
(((3225+14.7)* (460+44))/(460+78))-14.7=3020psi
In a mixture of air comprised of 20% oxygen and 80% nitrogen at an ambient pressure of 15 psia what is the partial pressure of oxygen in psia
15 psia x .20 = 3psia
Dalton’s law stays the total pressure exerted by a mixture of gases is equal to the _____ of the pressure of each of the different gases maxing up the mixture - each gas acts as it it _____ were present and occupied the total volume
Sum
Alone
A gas with 78% nitrogen at 66’ has what partial pressure of Nitrogen in psia
66’/33’ = 2 ata + 1 ata = 3 ata
(3.78)14.7psia= 34.39psia
Or
66’/33’ = 2ata + 1 ata = 3 ata
3*14.7 = 44.1 44.1*.78 = 34.39
Gas with 21% oxygen at 78’ seawater what is the partial pressure in psia
78/33 + 1 = 3.36ata
3.36ata * .21 = .7056 * 14.7psi = 10.37
Or
78 * .445 + 14.7 = 49.41psia
.21*49.41 = 10.37psia
Scuba cylinder is accidentally filled with 1% CO, if a diver breathes at a depth of 100’ seawater approximately what percentage of CO will he be breathing.
What percentage would the effect be at 100’
Still 1%
4% surface equivalency
If 1% of CO has 500,000 molecules at surface how many at 100’ of seawater
2,000,000 molecules
1.5% CO at surface would have same effect at 300’ as what %
300/33 +1 = 10ata
10* 1.5 = 15%
15%
Glass of water in a vacuum for several days so it no longer has any dissolved gas in it, it is then placed in a pressure pot and pressurized to 2ata for several days, what will be the gas pressure
2ata because there is a tendency of equilibrium to exist between the pressure within a liquid (gas tension) and the pressure of the gas in contact with that liquid
Henry’s law states the amount of gas that will dissolve into a liquid is almost ____ proportional to the _____ pressure of the gas.
Directly
Partial
If a glass of water placed in a pressure pot to 2 ata is then increased, the pressure of the gas within the liquid will
Pressure increases
Think of opening bottle of soda when open the pressure of the carbon dioxide decreases because the pressure of the gas in contact with the soda decreased, eventually it will reach equilibrium and go flat
Henry’s law is a direct relationship
Vacuum created in pressure pot the pressure of the gas within the liquid will
Decrease
80% nitrogen has a partial pressure at sea level in ata?
What is the total gas partial pressure in ata?
.80 x 1 = .8ata
0.8ata
1ata
When our tissues can’t hold any more gas pressure at sea level our body is ______
Saturated
______ is when there is no more gas exchange with a liquid
Saturation
When the gas in contact with tissue decreases the gas tension within the tissues also decrease which is called
Decompression
When breathing at depth the tissues of a diver begin to take in additional gas pressure, if the diver stays long enough his tissues will equalize with the ambient pressure? T/F
True
Water conducts heat more easily than air because its ______ are closer together which makes it easier for heat (energy) to be conducted
molecules
Why can water absorb more heat than other liquids
The polar nature of the water molecule resulting from the hydrogen bond
The change of speed from light traveling through different densities causes the light wave to ____ or _____
Bend
Refract
Why are water molecules better at transmitting sound than air
They are closer together making it easier to transmit vibrations
Why can’t humans talk underwater
Because human vocal cords must initially produce sounds in air and are unable to initially produce sounds while underwater
In air sound travels _____ feet per second whereas in water it’s _____ feet per second
1100
4800
Why can depth be ignored when calculating buoyancy
Water is for all practical purposes incompressible
_______ pressure is synonymous with _____ pressure
Ambient
Absolute
By knowing the displacement of an object and using a constant density you can easily find out the buoyant force on any object immersed in fresh or salt water? T/F
True
Air consumption is a function of density? T/F
True
What two variables is the partial pressure of a gas dependent
The absolute pressure
Percentage of gas in question
Colors are not as bright at depth due to
Absorption
Light travels in ______, the length of the light waves is determined by their _____. Colors on the ___ spectrum have more/less energy than colors on the ____ end. Wavelengths with with more/less energy are absorbed more easily and therefore are the first/last to fade.
Wavelengths Energy Red Less Blue Less First
Water has a much higher heat ____ than air
Capacity
Henry’s law states that the amount of gas that will dissolve into a solution is ____ proportional to the partial pressure of that gas and ____ proportional to the absolute temperature
Directly
Inversely
