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PADI Divemaster Course Chapter 9 Study Objectives/Self Assessments
Questions and Answers with Solutions
Why do you need a solid understanding of dive theory? -
ANSWER The more fluent you are with dive theory, the more
easily you can diagnose a problem, because you better grasp
the underlying causes.
A solid understanding of dive theory helps you: - ANSWER
Answer diver's questions, solve problems that aren't easily
predicted or predefined, understand relationships/causes and
effects in diving, function as a dive leader.
Why does water dissipate body heat faster than air does, and at
what rate does it do so? - ANSWER - Heat energy is the motion
of molecules, a denser substance has more molecules that must
be put into motion, so it absorbs more heat for a given volume
*Denser than air = more mass (molecules) for a given volume
*Water absorbs more heat than the same mass of air and most
other natural substances as it forms polar (weak) bonds
between its molecules that require energy to overcome, so
water requires more heat energy to raise a given temperature
*20 times faster than air does
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What affect does water's ability to dissipate heat have on a
diver? - ANSWER *Conduction: transmission of heat through
contact
*Convection: transmission assisted by the flow of a fluid; the
fluid in contact with the body becomes warmer, making it less
dense causing the water to rise, so cooler water flows in to
replace it, creating a continuos cooling cycle
-Contributes to cooling when you sit still in water when you're
not wearing an exposure suit.
-Average diver will be dangerously cold in half an hour in
16C/60F water and only survive an hour in 4C/40F water -
27C/80F is an enjoyable dive temperature without insulation
(you can stay in this indefinitely with a dry suit and thick
undergarment) even in exposure suits you continue to cool
What does light do when is passes from air into water, or vice-
versa, and how does this affect a diver? - ANSWER It refracts
(bending of light), the speed of light travels changes, causing it
to alter direction slightly unless its path is perpendicular to the
surface
-Magnifies by a ratio of 4:3 (fish thats 4 meters away appears to
be 3 meters away) 25% closer or 33% larger
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-Most affected when light passes from water to the air space in
your mask or camera housing
-Visual reversal: particles in water that resembles the haze we
see in air over long distances, so it looks farther away than it is
(lol i cant see that far anyways)
Why does sound travel faster in water than air, and
approximately how much faster is it in water? - ANSWER Sound
travels slightly 4x faster in water than in air
-Its a mechanical energy (pressure wave or p-wave) that moves
through matter
-The denser a material the better sound travels through it -
elasticity of a substance that determines how well sound travels
through it - more dense = better elasticity (except carbon and
lead)
-Water has more elasticity than air, which is why sound travels
faster through it
How does the speed of sound in water affect hearing? -
ANSWER The brain interprets sound direction based on the
slight differences in intensity and time of the sound that
reaches the ear
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-Underwater these differences are indiscernible, so you
perceive sounds as being directly overhead
Water dissipates body heat faster than air does, because it
absorbs heat approximately ______ times faster than air does. -
ANSWER 20
Because water dissipates body heat faster than air does, a
temperature that is comfortable and warm for an unprotected
diver in air will, for an unprotected diver, - ANSWER Quickly
become uncomfortable and cool in water.
Light _________ when it passes through a substance of one
density into a substance of a different density. - ANSWER
Changes speed, changes direction. (a. and b. but not c.)
Due to refraction, underwater objects appear to be magnified
by a factor of _______. - ANSWER 4/3
Sound travels faster in water than in air, because water is
denser (has more elasticity, to be more precise) than air does: -
ANSWER True
PADI Divemaster Course Chapter 9 Study Objectives/Self Assessments
Questions and Answers with Solutions
Why do you need a solid understanding of dive theory? -
ANSWER The more fluent you are with dive theory, the more
easily you can diagnose a problem, because you better grasp
the underlying causes.
A solid understanding of dive theory helps you: - ANSWER
Answer diver's questions, solve problems that aren't easily
predicted or predefined, understand relationships/causes and
effects in diving, function as a dive leader.
Why does water dissipate body heat faster than air does, and at
what rate does it do so? - ANSWER - Heat energy is the motion
of molecules, a denser substance has more molecules that must
be put into motion, so it absorbs more heat for a given volume
*Denser than air = more mass (molecules) for a given volume
*Water absorbs more heat than the same mass of air and most
other natural substances as it forms polar (weak) bonds
between its molecules that require energy to overcome, so
water requires more heat energy to raise a given temperature
*20 times faster than air does
, Page |2
What affect does water's ability to dissipate heat have on a
diver? - ANSWER *Conduction: transmission of heat through
contact
*Convection: transmission assisted by the flow of a fluid; the
fluid in contact with the body becomes warmer, making it less
dense causing the water to rise, so cooler water flows in to
replace it, creating a continuos cooling cycle
-Contributes to cooling when you sit still in water when you're
not wearing an exposure suit.
-Average diver will be dangerously cold in half an hour in
16C/60F water and only survive an hour in 4C/40F water -
27C/80F is an enjoyable dive temperature without insulation
(you can stay in this indefinitely with a dry suit and thick
undergarment) even in exposure suits you continue to cool
What does light do when is passes from air into water, or vice-
versa, and how does this affect a diver? - ANSWER It refracts
(bending of light), the speed of light travels changes, causing it
to alter direction slightly unless its path is perpendicular to the
surface
-Magnifies by a ratio of 4:3 (fish thats 4 meters away appears to
be 3 meters away) 25% closer or 33% larger
, Page |3
-Most affected when light passes from water to the air space in
your mask or camera housing
-Visual reversal: particles in water that resembles the haze we
see in air over long distances, so it looks farther away than it is
(lol i cant see that far anyways)
Why does sound travel faster in water than air, and
approximately how much faster is it in water? - ANSWER Sound
travels slightly 4x faster in water than in air
-Its a mechanical energy (pressure wave or p-wave) that moves
through matter
-The denser a material the better sound travels through it -
elasticity of a substance that determines how well sound travels
through it - more dense = better elasticity (except carbon and
lead)
-Water has more elasticity than air, which is why sound travels
faster through it
How does the speed of sound in water affect hearing? -
ANSWER The brain interprets sound direction based on the
slight differences in intensity and time of the sound that
reaches the ear
, Page |4
-Underwater these differences are indiscernible, so you
perceive sounds as being directly overhead
Water dissipates body heat faster than air does, because it
absorbs heat approximately ______ times faster than air does. -
ANSWER 20
Because water dissipates body heat faster than air does, a
temperature that is comfortable and warm for an unprotected
diver in air will, for an unprotected diver, - ANSWER Quickly
become uncomfortable and cool in water.
Light _________ when it passes through a substance of one
density into a substance of a different density. - ANSWER
Changes speed, changes direction. (a. and b. but not c.)
Due to refraction, underwater objects appear to be magnified
by a factor of _______. - ANSWER 4/3
Sound travels faster in water than in air, because water is
denser (has more elasticity, to be more precise) than air does: -
ANSWER True
