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48 Cards in this Set
- Front
- Back
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Principle of Buoyancy
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an object placed in water is buoyed up by a force equal to the weight of the quantity of water it displaces
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An object displaces an amount of water weighing _______ than its own weight it will float. What is this called?
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more: Positive buoyant
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An object displaces an amount of water weighing less than its own weight it will ______. What is this called?
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sink: Negatively buoyant
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An object displaces an amount of water equal to its own weight it will _____. What is this called?
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remain suspended in the water: Neutrally buoyant
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What skill allows you to control where you are in the water?
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Buoyancy control; on of the most important skills to master
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_________ buoyancy at the surface helps save energy.
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positive
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Advantages of being neutrally buoyant under water
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swim effortlessly and move freely in all directions; keeps you off the bottom
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Equipment used to control buoyancy
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lead weights and buoyancy control device (BCD)
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An object is more buoyant in salt water than _____ water.
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fresh
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What happens to lung volume when you exhale?
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Lung volume decreases when you exhale making you less buoyant. (sink)
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How do you fine-tune your buoyancy?
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by breathing more deeply or more shallowly you can fine-tune your buoyancy
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Why don't you usually feel pressure?
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the body is mostly liquid distributing pressure equally; the air spaces have air pressure inside equal to air pressure outside
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Why are pressure changes more significant in water for a given ascent or descent than the same distance ascent or descent in air?
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Water is more dense and heavy than air
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Depth = 33ft Pressure = _____ Air Density = ______
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2 bar/ata X2
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Depth = 132ft Pressure = _____ Air volume = ____
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5 bar/ata 1/5
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Depth = _____ Pressure = 3 bar/ata Air Density = ______
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66ft X3
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Depth = ____ Pressure = _____ Air volume = 1/4
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99ft 4 bar/ata
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As you ascend air will ______ because pressure ________.
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air will expand and pressure will decrease
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What are the two major air spaces within your body most noticeably affected by increasing pressure?
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ears and sinuses
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What is the major artificial air space most affected by increasing pressure?
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mask
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What is a squeeze? Where can they occur?
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A squeeze is a pressure imbalance in which pressure outside an air space exceeds pressure inside an air space, resulting in pain or discomfort. A squeeze can be in the ears, sinuses, mask, lungs, teeth, or any other air space
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How do you prevent a squeeze?
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keep the volume normal by adding air during descent (equalization) Lungs: breathe continuously Ears: pinch nose and blow against in with mouth closed, swallow, wiggle jaw from side to side Mask: exhale through nose
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What is equalization?
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keep the volume normal by adding air during descent
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When should you equalize?
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every few feet you should equalize before discomfort
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What should you do if you can not equalize?
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ascend until you relieve the discomfort, if you can't equalize discontinue the dive. After equalization continue a slow descent equalizing more frequently
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What is the most important rule in scuba diving?
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Breathe continuously and never hold your breath
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What causes lung over expansion injuries?
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Ascending while holding your breath
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What is a reverse block?
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pain and discomfort caused by expanding air trapped inside an air space during ascent
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If you feel reverse block discomfort during ascent what should you do?
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slow or stop you ascent, descend a few feet and give the trapped air time to work its way out
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You consume (faster/slower) air as you go deeper.
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faster
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How should you breathe in dense air?
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deep and slow
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As you go deeper what happens to the density of the air?
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air becomes more dense as you go deeper making in harder to inhale and exhale. It takes about four times the effort to breathe twice as fast. You should take deep, slow breaths and save energy
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What should your rate of accent be?
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no faster than 60 feet per minute
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In cold water you should add how many feet when planning a dive?
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10 feet
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When should you plan deeper dives when doing multiple dives?
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first
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What is the maximum depth for open water divers?
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60feet; advanced: 100 feet; never exceed 130 feet
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When should you make a safety stop?
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after any dive 100 feet or greater and any time you surface within 3 pressure groups of a no-decopression limit (NDL)
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How is a safety stop performed?
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stop for 3 minutes at 15 feet
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What do you do if you dive deeper than 130 feet?
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Immediately ascend at normal rate to 15 feet and make an emergency decompression stop for 8 minutes followed by a surface interval of at least 6 hours.
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What is Risidual Nitrogen Time (RNT)?
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An amount of nitrogen, expresed in minutes for a specific depth, that you add to the actural bottom time of a dive to account for residual nitrogen from a previous dive
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How do you figure Total Bottom Time (TBT)?
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It is the sum of Residual Nitrogen Time and Actural Bottom Time after a repetive dive, used on Table 1 to detrmine the pressure group
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What is a Pressure Goup?
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A letter used on the Recreational Dive Planner to designate the amount of theoretical residual nitrogen in your body
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What is a no-stop dive?
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a dive made within no decompression limits doesn't require emergency decompression stops
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What is No Decompression Limit (NDL)?
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the maximum time that can be spent at a depth before decompressin stops are required. Also called "no-stop time"
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What is a Dive Profile?
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a drawing of your dive plan, used to avoid confusion and omissions when using the dive tables
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What is Actual Bottom Time?
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In repetivie diving, the total time actually spent under water from the beginning of descent until leaving the bottom for a direct continuous ascent to the surface or safety stop
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What is Adjusted NO Decompression Limit?
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the time limit for a repetive dive that accounts for residual nitrogen, found on Table 3. Actual Bottom Time should never exceed the adjusted no decompression limit
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What is Bottom Time?
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time from the beginning of descent until the beginning of a direct, continous ascent to the surface or safety stop
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