Your assignment is to listen to the three recordings, one at a time, and read this webpage as you listen. You are also supposed to copy the notes at the end of each recording. When you finish copying the notes, go back over the reading material and study the pictures and charts so that you understand what you have read. You may also want to listen to the recording again.
The Physics of the Ocean
If you have ever been to the ocean it
seemed to be constantly in motion. Waves
rush across its surface and crashes against the land. “Rivers” of cold or warm water snake along its
surface. Twice a day, the ocean creeps
up the beach and twice a day it creeps backward. Lets’ learn what causes these constant
changes.
Hey!
Remember when we discussed that the SUN is the source of all energy here on
Earth? Well, here is more evidence. The Sun is directly responsible for waves and
currents, and a little involved in the tides. Pay attention and see how.
CURRENTS
Ocean water is never still. It is constantly moving in
enormous “rivers” called currents. These currents circulate throughout the
oceans of our world like the blood that moves through our body. Even though the
oceans are broken up by continental landmasses, a drop of ocean water could
travel from one end of the Earth to the other. Ocean water is mixed by the
currents into one huge planetary ocean.
Two great forces create ocean currents. The Prevailing
Winds and the Coriolis effect. The Prevailing Winds are like a breath over the ocean. They move continuously
in the same general direction and move the water. The two most predictable
Prevailing Winds are the Trade Winds,
which blow from east to west toward the equator, and the Westerlies, which blow from west to east in the middle
latitudes of the Earth. . The Westerlies are found
approximately 45 degrees north and south of the equator. Early explorers like Columbus and Magellan
were able to travel from continent to continent because they had a true
understanding of the location of the prevailing winds of the world. These winds
blow almost daily in the same direction and can be found at specific locations
on our planet. Remember, early explorers knew that the trade winds blow near
the equator in both the Northern and Southern Hemispheres and the Westerlies are found approximately 45 degrees north and
south of the equator.
The Coriolis effect is
caused by the rotation of the Earth. This force directs the flow of the ocean
currents. Water north of the equator moves in a clockwise direction, while water
south of the equator moves in a counter-clockwise direction. Global winds
blowing in opposite directions in combination with the rotation of the Earth
cause a powerful system of rotating currents called gyres. One of
the most well known gyres in the world is the
Let’s make sure we understand gyres. A gyre is a giant current that is traveling
in a circle. The gyre is pushed along by
the Trade Winds, the Westerlies, and is being spun in
a circle by the coriolis effect.
There are two basic types of ocean currents: surface
currents and density currents. Surface currents are wind driven currents. These
currents can be more than 50 miles wide and can flow at speeds of about 136
miles per day. The maximum depth of surface currents is not more than 100 – 200
meters. The water temperature of surface currents may
range from a low of 30° F to a high of 86° F. Surface currents are important because they regulate the water
temperature throughout the world. They distribute the sun’s heat so that the
Tropics don’t get too hot and the
Density currents flow in the deep water of the ocean below
the surface currents. Density currents are affected by temperature and
salinity. Cold water is denser than warm water because the molecules are packed
more closely together in a given volume. Greater salinity also increases
density, so water that is cold and salty sinks under warmer, less salty water.
This sinking is a major triggering force of ocean currents. Cold water at the
poles sinks and slowly moves toward the equator. Warm water currents travel out
from the equator along the surface, flowing toward the poles to replace the
sinking cold water.
One final fact about the
currents, we have learned that they are caused by the wind and by differences
in density. We have learned that their
direction is affected by the prevailing winds and by the corioilis effect. There is one more major factor
in current direction and that is continental deflection. Continental deflection occurs when a current
flows up against a continent. Obviously
the current cannot go through the continent, so it gets its direction changed
or “deflected” by the continent. Sort of
like spraying a water hose on the side of a building, the water bounces off.
2. current is a stream of
water flowing like a river in the ocean.
3. ocean currents can carry
warm water towards cold climates and can carry cold water towards warm climates
4. surface currents are
caused by the wind.
5. coriolis effect-the curving of winds and ocean currents caused by the Earth's rotation.
6. Gulf Stream-100 km wide surface current in the Atlantic Ocean that carries warm water up from the equator.
7. drift bottle- bottle containing a message that is dropped into a current to track its movement.
8.
Gyre: Surface currents that are wind
driven and move in large circular patterns
9.
North Atlantic Current is a gyre that takes warm water up to
10. continental deflection-when a current changes direction because it flowing towards a continent
11. density current-caused by
the differences in cold and hot water and/or salty and fresh water.
12. salt water is more dense
than fresh water so salt water will sink down below fresh water
13. cold water is more dense
than warm water so cold water will sink down below warm water.
14. density will cause the movement of water just as surely as wind will cause movement.
15. upwelling-the vertical circulation in the ocean that brings deep, cold water to the surface.
16. upwelling brings nutrients up from the ocean floor which creates rich fishing grounds.
17. as seawater freezes, the salt is left behind causing the remaining water to be extra salty. The extra salty water is more dense and will sink, creating a density current.
18. rapid evaporation also causes density currents. When ocean water evaporates, the salt is left behind, making the remaining water salty and more dense.
To learn more about currents, go here and do a
little research. You may prepare a
foldable for extra credit it you want to.
http://www.oar.noaa.gov/k12/html/oceancurrents2.html
WAVES
A wave can be a
friendly gesture to a passing friend, it can be a movement through a crowd at a
football game, and most of us think of the ocean. But, what is a wave really? A wave
is a disturbance that transfers energy through matter or space. In other words, a wave carries energy.
Standing in the sand
on the beach, you watch as the waves roll to the shore and crash one after
another, in an endless rhythm. Something has transferred energy into the sea to
produce the waves. In most cases, that
something is the wind. But wind is air
that has been made to move by energy from the SUN. SOOOO, indirectly, most waves are produced by
the sun’s energy. Waves moving across
the ocean carry the energy of the wind, but the ocean water does not move along
with the wave. As the energy of a wave moves toward the shore, the particles of
water move up and down in a complete circle. Only the energy of the waves moves
forward. A wave is simply a pulse of energy that moves from one particle of
water to the next. When a wave passes through the water, the water simply rises
up, and then comes down again in the same place. In one complete wavelength, a
molecule of water moves through a complete circular path and ends up at the
same place that it started. Think about it, have you ever watched a seagull
sitting on a wave bobbing up and down?
The seagull will bob up and down because only the energy is moving
forward, not the actual water itself. Only the wave itself travels forward. You can
demonstrate this by tying a rope to a tree. Pull the rope tight and shake it up
and down. A wave is created that moves forward until it strikes the tree, but
the rope itself does not move forward. The energy of the wave simply moves
forward through the particles of the rope.
Most waves are formed by the wind blowing across the
surface of the water. The moving air
particles rub against particles of water creating friction. The wind is actually dragging the water
along. The harder and longer the wind
blows, the higher the wave. The waves
will gradually get bigger and bigger.
)
All waves possess
certain characteristics. The wave crest is the top or highest
point of the wave. Conversely, the trough is the lowest point of the wave. The distance from the crest of one wave to the crest of the next wave is
the wavelength. The
wavelength can vary from a few feet to a few hundred yards. The vertical distance from the crest to the
trough of the wave is the wave
height. The distance the wind blows, the speed of the wind, and
the length of the time the wind blows determines the height of a surface wave
on the ocean. It is interesting to note that in deep water, there is virtually
no wave action.
Another
characteristic is wave period, which is the time it takes for
successive wave crests to pass a certain point. Wave period is often confused
with wave frequency, the
number of waves that pass a certain point in a given amount of time. Think
of it this way, period is how long and frequency is how many, so 1st
period science lasts 60 minutes that is the period and you have science 5 times
a week, that is the frequency.
In open water waves
can travel for thousands of miles. When a wave approaches the shore and passes
through more shallow water the energy of the wave slows down. The waves become
closer together. The wave height increases and the wavelength decreases. The
lower part of the wave starts to drag and the top part keeps going so the wave
curls over itself and breaks crashing into the shore. The wave is actually
falling forward. We call these falling waves, breaker waves. Think about it, if you have ever been body
surfing at the beach, if you go out a little too far, all you do is bob up and
down. If you are too close in, you just
get splashed. BUT, if you catch the wave
just as it breaks, you get pushed ashore by the “falling wave”. Breaker waves are lower in areas that have a
wide Continental Shelf and higher in areas with a narrow Continental Shelf. Remember our map of the ocean floor, the
continental shelf off the coast of
The
constant wave breaking action is known as surf. Over time, the ceaseless
breaking action of the surf wears away large rocks and breaks them down into
smaller and smaller rocks. Eventually, these rocks will be broken down into
particles of sand. This process takes hundreds or thousands of years depending
upon the type of rocks and minerals. The surf also moves sand on the beach from
place to place. Storms, large waves, and wind carry the sand from one spot to
another on the beach or they wash large quantities of sand out to sea. In
September 2004, a series of hurricanes washed miles of protective sand dunes
out to sea along the Gulf Coast of Florida. Each year, towns and communities
(especially along the eastern coast of the
13. waves-the
regular up and down movement of water
14. crest
is the highest point of a wave
15. trough
is the lowest point of a wave
16. wavelength
is the distance from one crest to the next.
17. wind
causes waves.
18. frequency
is the number of waves that occur in a certain period of time.
19. energy
travels in the direction of the wave.
20. water particles do not
move with the wave, they move in circles equal to the height of the wave
21. ocean
currents flow in a clockwise direction in the Northern Hemisphere. Currents flow in a counterclockwise direction
in the Southern Hemisphere.
22. coriolis effect causes the winds and the currents to curve.
Another way of
measuring the height of waves is with the Beaufort Scale.
It was developed in the early 1880s by Admiral Francis Beaufort to indicate the
strength of wind at sea. The scale uses the numbers from 0 to 12 to show how
strong the wind is and the effect of wind speed on wave height. By the way, a knot is just a little faster than
a mph. 10 knots is about 11.5 mph.
Beaufort Wind Scale
|
Beaufort |
Windspeed |
Description |
Sea Condition |
|
0 |
0 |
Calm |
Sea like a mirror |
|
1 |
1 - 3 |
Light Air |
Ripples but without foam crests |
|
2 |
4 - 6 |
Light Breeze |
Small wavelets. Crests do not break |
|
3 |
7 - 10 |
Gentle Breeze |
Large wavelets. Perhaps scattered white horses |
|
4 |
11 - 16 |
Moderate Breeze |
Small waves. Fairly frequent white horses. |
|
5 |
17 - 21 |
Fresh Breeze |
Moderate waves, many white horses |
|
6 |
22 - 27 |
Strong Breeze |
Large waves begin to form; white foam crests, probably
spray |
|
7 |
28 - 33 |
Near Gale |
Sea heaps up and white foam blown in streaks along the
direction of the wind |
|
8 |
34 - 40 |
Gale |
Moderately high waves, crests begin to break into
spindrift |
|
9 |
41 - 47 |
Strong Gale |
High waves. Dense foam along the direction of the wind.
Crests of waves begin to roll over. Spray may affect visibility |
|
10 |
48 - 55 |
Storm |
Very high waves with long overhanging crests. The
surface of the sea takes a white appearance. The tumbling of the sea becomes
heavy and shock like. Visibility affected |
|
11 |
56 - 63 |
Violent Storm |
Exceptionally high waves. The sea is completely covered
with long white patches of foam lying in the direction of the wind.
Visibility affected |
|
12 |
64+ |
Hurricane |
The air is filled with foam and spray. Sea completely
white with driving spray. Visibility very seriously affected. |
Source: http://www.r-p-r.co.uk/beaufort.htm
TIDES
Although the wind plays a major role in most ocean motion,
it is not the predominant cause of tides, the slow, periodic rise and fall of
ocean waters.
The
water level of the ocean rises and falls throughout the day. Early in the day, ocean water rises and
covers part of the beach. Later in the
day, the ocean level falls. The beach is
exposed. These regular changes in ocean
water levels are called tides. A low
water level is called low tide. A high
water level is called high tide.
A tide is a rise or fall of the ocean’s surface caused
mostly by the gravitational pull of the moon.
The gravitational pull of the sun also affects a tide, but not as much
as that of the moon.
Tides are caused by two
factors: the gravitational pull of the Moon and Sun and the inertia of water in
the oceans on Earth. The combination of gravity and inertia are responsible for
the creation of two major tidal bulges on the Earth. Gravity creates a bulge of
water on the side of the Earth facing the Moon and inertia creates a bulge on
the side of the Earth facing away from the Moon. The sun also affects the size
and position of the two tidal bulges.
The Sun, Moon, and Earth are three extremely large objects
separated by very great distances. Despite the large distances between them,
each object affects the others. Earth is kept in orbit around the sun by the
gravitational forces between them. The Moon is kept in orbit around the Earth
by the gravitational forces between them. These forces are mutual, meaning each
object attracts and is attracted to the other. However, the gravitational pull
of the Sun is almost 200 times greater than the Moon, but since the Moon is
almost 400 times closer to the Earth than the Sun, the Moon’s gravitational
pull is more than twice that of the Sun.
Click on the link below to
see the tides in motion;
http://www.sfgate.com/getoutside/1996/jun/tides.html
Most coastal areas, with some exceptions along the coast of
Four times a month, the Sun’s effect on tides is
noticeable. Twice a month, the Sun, Moon, and Earth align to produce very high
and very low tides called Spring Tides. The name has nothing to
do with the season. Spring is from a Saxon word meaning “to swell”. Spring
Tides occur during the New Moon and Full Moon. When the Sun and Moon are at
right angles to each other, the gravity of each pulls the ocean water in different
directions. In this position, there is little difference between the depth at high and low tide. These tides are called Neap
Tides. Neap is from a Saxon word meaning “scarce or lacking”. Neap
Tides occur twice a month, during the first and third quarter phases of the
Moon. Spring and Neap Tides occur twice every 29.5 days (or twice each month).
23. tides-the regular
change in the level of Earth’s oceans.
24. flood
tide-the incoming, or rising tide
25. ebb
tide-outgoing, or falling
tide
26. Moon’s gravity causes
most tides.
27. changing
tides happen about every 6 hours and 15
minutes.
28. Spring tide is an
extra high and extra low tide caused by the alignment of the Moon and the Sun.
29. Neap tide is smaller tidal change than normal
caused by the Moon and Sun being on different sides of the Earth.
30. intertidal zone-the land that is exposed during low
tide but is covered during high tide.
Tidal Geography
It
is worth noting that other factors can affect tides. The shape of bays and
estuaries can magnify the intensity of tides. Funnel-shaped bays can
dramatically alter
tidal magnitude. The
We
have talked about tides and waves, but what is a “tidal wave”? Tidal waves are actually seismic sea waves or
tsunamis. Students may want to read more about this phenomenon.
Some of the largest
and most destructive ocean waves are not formed by wind. They are caused by
movements of the Earth’s crust, such as earthquakes on the ocean floor.
STOP! Copy your notes.
STOP! Copy your notes.
1. What are tides?
2. What causes tides?
3. How many tides occur each day?
4. Name three tides that occur, tell when they occur, and
how they occur.
5. Which of these tides is the strongest?
6. How often do each of these tides occur?
Glossary of Terms
Coriolis
effect: A force that is caused by the
spinning of the Earth. In response to the movement of the Earth, ocean currents
flow in a clockwise direction in the Northern Hemisphere and in a
counterclockwise direction in the Southern Hemisphere.
Gyre: Surface currents that are wind driven
and move in large circular patterns.
Neap
tide: The smallest rise and fall in tides that occur when the sun and the
moon are at right angles to the Earth.
Prevailing
winds: Prevailing winds consistently blow in a particular
direction. The trade winds and westerlies are prevailing winds.
Spring
tide: The greatest rise and fall in tides that occur when the sun and the
moon are in line with the Earth.
Trough: The
lowest point in a wave between crests.
Tsunami: The
Japanese word for seismic sea wave. A series of traveling ocean waves of
extremely long length generated by disturbances associated primarily with
earthquakes occurring below or near the ocean floor. Underwater volcanic
eruptions and landslides can also generate tsunamis.
Wave
crest: The top of a wave.
Wave
frequency: The number of waves that pass a given point per
second.
Wave
height: The vertical distance between the crest and trough of
a wave. This distance is measured from the back of the wave.
Wavelength: The
horizontal distance between two successive wave crests or troughs.
Wave
period: The time it takes for successive wave crests to pass a
certain point.