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The Physics of Water
Chapter 7 Pages 7-3 to 7-5
The Physics of Water
Heat and Heat Capacity
 HEAT is simply the transfer of energy from a hot object to a colder
object.
 Thermal energy is measured based on both the quantity and speed of
vibrating molecules.
 Temperature is a number that is related to the average kinetic energy
of the molecules of a substance.The two most common temperature
systems are Fahrenheit and Celsius. Celsius is most used in
science because it is based on water’s physical properties.
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7-3
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7-4
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7-5
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Chapter 7 Page 7-6
The Physics of Water
Heat and Heat Capacity (continued)
n Heat capacity of a substance is the amount of heat energy required to
raise change one gram of a substance by 1°C.
 It’s expressed as the number of calories required.
 It takes more heat energy to raise water’s temperature than that of
most substances.
 Water’s heat capacity affects the world’s climate and weather.
n Heat is carried to areas that would otherwise be cooler, and
heat is carried away from areas that would otherwise be hotter.
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Chapter 7 Pages 7-7 to 7-11
The Physics of Water
Water Temperature and Density
n As water cools it becomes denser down to 3.98°C (39.16°F) Below this
point, it crystallizes into ice. As water moves into a solid state* it
becomes less dense.
n Ice does not form all at once at the freezing point of 0°C (32°F), but
crystallizes continuously until all liquid turns solid. Temperature does
not drop any further until all the liquid water freezes, even though heat
continues to leave.
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Water Temperature and Density
Chapter 7 Pages 7-7 to 7-11
The Physics of Water
Latent Heat of Vaporization
n Latent heat of vaporization is the heat required to change water to a
liquid from a gas or a gas to a liquid.
n Latent Heat of Fusion is the energy required when water melts from ice
to liquid or freezes from liquid back to ice
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HEAT vs TEMPERATURE
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7 - 11
1 -How much energy to change 1g water from solid to water?
2 - How much energy to change 1 g water from liq to gas?
3 - How much energy to change 1g ice at 0 deg to 100 deg gas? Assume 100% ice
to 100% gas
4 – How much energy to change #3 back to 100% ice?
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Chapter 7 Pages 7-11 & 7-12
The Physics of Water
Thermal Inertia
n
n
n
The tendency of water to resist temperature change is called thermal inertia.
Thermal equilibrium means water cools at about the same rate as it heats.
These concepts are important to life and Earth’s climate because:
 Seawater acts as a global thermostat, preventing broad temperature
swings.
n Temperature changes would be drastic between night and day and
between summer and winter.
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Ocean Water Density
n
n
Seawater density varies with salinity and temperature.
 This causes seawater to stratify, or form layers.
Dense water is heavy and sinks below less dense layers. The three
commonly found density layers are:
 2. Thermocline – separates the surface zone from the deep zone. It only
needs a temperature or salinity difference to exist. This zone makes up
about 18% of the ocean’s volume.
Chapter 7 Pages 7-13 & 7-14
The Physics of Water
 1. Surface zone – varies in places from absent to 500 meters (1,640
feet). In general it extends from the top to about 100 meters (328 feet).
This zone accounts for about only 2% of the ocean’s volume.
 3. Deep zone – lies below the thermocline. It is a very stable region of
cold water beginning deeper than 1,000 meters (3,280 feet) in the middle
latitudes, but is shallower in the polar regions. The deep zone makes up
about 80% of the ocean’s volume.
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Chapter 7 Pages 7-16 to 7-20
How Water Physics Affect Marine Life
Light
n Water scatters, reflects and absorbs light. When light reaches the
water’s surface, some light penetrates, but, depending on the sun’s
angle, much may simply reflect back out of the water.
 Within the water, light reflects off light-colored suspended particles.
 Dark colored suspended particles and algae absorb some of the
light.
 Water molecules absorb the energy, converting light into heat.
 Water absorbs colors at the red end of the spectrum more easily
than at the blue end, this is why the water looks blue.
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Chapter 7 Pages 7-16 to 7-20
How Water Physics Affect Marine Life
Light
n Two zones exist with respect to light penetration:
 1. Photic Zone – where light reaches (can be as deep as 200
meters (656 feet). The photic zone has two subzones.
n Euphotic Zone – the upper shallow portion where most
biological production occurs – comprises about 1% of the
oceans.
n Dysphotic Zone – where light reaches, but not enough for
photosynthetic life.
 2. Aphotic Zone – it makes up the vast majority of the oceans.
Where light does not reach and only a fraction of marine organisms
live.
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n
Chapter 7 Pages 7-21 & 7-22
How Water Physics Affect Marine Life
Temperature
Compared to land-based climates, marine organisms live in a much less
challenging environment with respect to temperature range.(Why?)
 Ectotherm – An organism who's internal temperature changes with
seawater temperature. Commonly called “cold-blooded.”
 Endotherm – Organisms that have an internal temperature that varies, but
remains 9°-16°C (48.2°- 60.8°F) warmer than the surrounding water.
 Homeotherm – Have an internal temperature that is relatively stable. They
are called “warm-blooded”; marine mammals and birds are in this category.
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n
Chapter 7 Pages 7-21 & 7-22
How Water Physics Affect Marine Life
Temperature
n
Temperature affects metabolism – the higher the temperature within an
organism the more energy-releasing chemical processes (metabolism) happen.
 Endotherms and homeotherms can tolerate a wide range of external
temperatures.
Internal heat regulation allows endotherms an advantage.
 Their metabolic rate remains the same regardless of external
temperature allowing them to live in a variety of habitats.
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n
Chapter 7 Pages 7-22 to 7-24
How Water Physics Affect Marine Life
Sound
Sound travels five times faster in water than in air.
 It travels through warm water faster than cool… but it travels faster in deep water due
to pressure.
 Sound bounces off suspended particles, water layers, the bottom and other obstacles.
 Sound travels much farther through water than light does.
 Sound is eventually absorbed by water as heat.
n
Because sound travels so well in water, marine mammals use echolocation to
sense an object’s size, distance, density, and position underwater.
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Chapter 7 Pages 7-25 to 7-27
How Water Physics Affect Marine Life
Pressure
Pressure exerted by water is called hydrostatic pressure. It’s simply the weight
of the water.
 For each 10 meters (33 feet) hydrostatic pressure is equal to atmospheric
pressure – 1 bar/atmosphere
 At 10 meters (33 feet) the total pressure is 2 bar – 1 bar from atmospheric
pressure plus 1 bar from hydrostatic pressure.
 A marine organism living at 10 meters (33 feet) experiences twice the
pressure present at sea level. Pressure increases 1 bar for each additional
10 meters (33 feet).
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n
Chapter 7 Pages 7-25 to 7-27
How Water Physics Affect Marine Life
Pressure
Hydrostatic pressure doesn’t affect marine organisms because it is the same
inside the organism as outside.
 Living tissue is made primarily of water, which (within limits) transmits
pressure evenly. Since it’s in balance, pressure doesn’t crush or harm
marine organisms.
 Hydrostatic pressure is primarily an issue only for organisms that have gas
spaces in their bodies.
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n
Chapter 7 Pages 7-28 to 7-31
How Water Physics Affect Marine Life
Size and Volume
Using a sphere to substitute for a cell:
 The volume of a sphere increases with the cube of its radius and the
surface area increases with the square of its radius.
n If a cell were to increase diameter 24 times original size, the volume would
increase 64 times, but the surface area would increase only 16 times.
 High surface-to-volume ratio is important for cell function. The bigger the cell,
the lower the surface-to-volume ratio, which means that there’s less relative
area through which to exchange gases, nutrients, and waste.
n This is why large organisms are multicellular rather than a giant single cell.
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n Buoyancy
n
Chapter 7 Pages 7-28 to 7-31
How Water Physics Affect Marine Life
Size and Volume
Archimedes’ Principle states that an object immersed in a gas or liquid is
buoyed up by a force equal to the weight of the gas or liquid displaced.
 This means marine organisms don’t have to expend much energy
to offset their own weight compared to a land-based existence.
n It allows entire communities to exist simply by drifting.
n It allows organisms to grow larger than those on land.
n It allows many swimming creatures to live without ever actually coming
into contact with the bottom.
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Movement and Drag
n
Chapter 7 Pages 7-31 & 7-32
How Water Physics Affect Marine Life
n
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Marine organisms avoid sinking by:
 Plumes, hairs, ribbons, spines, and other protrusions that increase their
drag and help them resist sinking.
 Others have buoyancy adaptations that help them remain suspended in the
water column.
Some marine organisms need to overcome drag as they swim. Adaptations
that help them overcome drag:
 Moving or swimming very slowly.
 Excreting mucus or oil that actually lubricates them to “slip” through the
water.
 The most common is to have a shape that reduces drag – streamlining.
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Currents
Chapter 7 Pages 7-31 & 7-32
How Water Physics Affect Marine Life
Movement and Drag
n
It is speculated that drifting provides several advantages.
 1. Drifting disperses organisms into new habitats, ensuring survival should
something happen to the original community.
 2. May take organisms into nutrient-rich areas, preventing too many
offspring from competing for the same resources in the original community.
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