Transcript The Physics of Water

The Physics of Water
Seawater’s chemical properties affect how
life functions in the oceans. Water’s physical
properties not only affect life processes of
marine organisms, but of human beings in
the water.
Heat and Heat Capacity
 Heat is the kinetic energy in the random movement, or
vibration, of individual atoms and molecules in a substance.
 The faster molecules move, the more heat there is. Total heat
energy is measured based on both the quantity and speed of
vibrating molecules.
 Temperature measures only how fast the molecules vibrate.
 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.
Heat and Heat Capacity (continued)
 Heat capacity of a substance is the amount of heat
energy required to raise a given amount of a substance
by a given temperature.
 Scientists express heat capacity in terms of the amount
of heat energy it takes to 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.
 Therefore water can absorb or release a
lot of heat with little temperature change.
 Water’s heat capacity affects the
world’s climate and weather.
 Heat is carried to areas that would otherwise
be cooler, and heat is absorbed in
areas that would otherwise be hotter.
Water Temperature and Density


As water cools it becomes denser. At 3.98°C (39.16°F) it reaches maximum density. Below
this point, it crystallizes into ice. As water moves into a solid state* it becomes less dense.
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.



This produces non-sensible heat – a change in heat energy that cannot be sensed with a
thermometer.
The non-sensible heat lost when water goes from liquid to solid state is called the latent heat of
fusion.
Sensible heat is that which you can sense with a thermometer.
* State is an expression of a substance’s form as it changes from solid, to liquid, to gas with the addition of heat.
Latent Heat of Vaporization

Latent heat of vaporization is the heat required to vaporize a substance.


It takes more latent heat to vaporize water than to freeze it because when water freezes only some of
the hydrogen bonds break.
When it vaporizes, all the hydrogen bonds must break, which requires more energy.
Thermal Inertia
 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.
 Temperature changes would
be drastic between night and day
and between summer and winter.
 Without the thermal inertia,
many – perhaps most – of the
organisms on Earth could not
survive the drastic temperature changes that would occur each night.
Ocean Water Density
 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:



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.
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.
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.
Light
 Water scatters 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.
 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.
 Euphotic Zone – the upper shallow portion where most biological production
occurs – comprises about 1%
of the oceans.
 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.
Temperature
 Compared to land-based climates, marine organisms live in a much less
challenging environment with respect to temperature range.
 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.
 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.
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.
 Because sound travels so well in water, marine
mammals use echolocation to sense an object’s
size,
distance, density, and position underwater.
Pressure
 Pressure exerted by
water is called
hydrostatic pressure.
It’s simply the weight of
the water.
 At 10 meters (33 feet)
hydrostatic pressure is equal to
atmospheric pressure – 1
bar/ata.
 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).
 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.
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.
 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.
 This is why large organisms are multicellular rather than a giant single
cell.
Buoyancy
•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.
•It allows entire communities to
exist simply by drifting. It
allows organisms to grow larger
than those on land. It allows
many swimming creatures to live
without ever actually coming into
contact with the bottom.
Movement and Drag
 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.
Currents
 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.