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 study the notes at the end of each recording. When you finish studying 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 (click to listen)

 

            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 Gulf Stream , which was first mapped by Benjamin Franklin. Originally, it was believed that the warm water of the Gulf Stream flowed out of the Gulf of Mexico , and thus its name. Later it was discovered that the Gulf Stream is part of the North Atlantic current system. It carries warm water from the Caribbean up the east coast of the United States, across the northern Atlantic, and over to the west coasts of England and Europe. The Gulf Stream is deep in places (over 2,500 feet) and flows as fast as 10 miles/hour. Other well-known currents include the California Current in the North Pacific Ocean that flows south along the west coast of North America and the Peru Current in the South Pacific that flows along the west coast of South America .

 

     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 Polar Regions don’t get too cold.

          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.

 

1. Ocean water is always moving

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 Northern Europe and gives it a warmer climate

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 (click to listen)

 

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.  

 

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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 Georgia sticks out pretty far into the ocean.  The west coast of the United States has good surfing waves because of the larger breaker waves because is has a very narrow Continental Shelf in the Pacific Ocean.

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 United States) spend large sums of money to erect barriers or to haul in new sand to rebuild their beaches, which are constantly being washed away by the waves.

 

If you lost your notes, copy these notes onto your paper.
 

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
Force

Windspeed
Knots

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

 

STOP!!! Copy the notes!!! Then listen to the next lesson.  

 

 

 

STOP! Now copy these notes. Remember, you can listen to the recordings as you copy the notes.  

 

 

 

 

 

 

 

 

TIDES (click to listen)

 

          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 Alaska and the Gulf of Mexico, experience two high tides and two low tides every lunar day. We are familiar with the 24-hour solar day, which is the time that it takes for a specific site on the Earth to rotate from an exact point under the sun to the same point under the sun. A lunar day is the time it takes for a specific site on the Earth to rotate from an exact point under the moon to the same point under the moon. Unlike a solar day, however, a lunar day is 24 hours and 50 minutes. The lunar day is 50 minutes longer than a solar day because the moon revolves around the Earth in the same direction that the Earth rotates around its axis. It takes the Earth an extra 50 minutes to catch up to the moon. Since the Earth rotates through two tidal bulges every lunar day, coastal areas experience two high and two low tides every 24 hours and 50 minutes. In other words, high tides occur 12 hours and 25 minutes apart. It takes six hours and 12.5 minutes for the water at the shore to go from high to low, or from low to high. Tide levels vary greatly throughout the world, from an average of 5 – 10 feet vertical change each day to a maximum of 56 feet in the Bay of Fundy, which separates New Brunswick from Nova Scotia.

 

          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 Bay of Fundy, mentioned above, is a classic example of this effect. It has the highest tides in the world. Narrow inlets and shallow water tend to dissipate incoming tides. Examples include inland bays such as Laguna Madre, Texas, and Pamlico Sound, North Carolina. In estuaries with strong tidal rivers, such as the Delaware River and Columbia River, powerful seasonal river flows in the spring can alter or mask the incoming tide. Local wind and weather patterns can also affect tides.

 

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. Seismic Sea Waves or Tsunamis are set in motion by earthquakes, underwater volcanic eruptions, or underwater landslides. Tsunamis can speed through the ocean at nearly 500 miles per hour and can rise as high as a 20-story building with a wavelength as much as 124 miles. When the wall slams onto the shore it causes mass destruction. The largest Tsunami on record occurred in 1971 off Ishigaki Island in Japan. It was an amazing 278 feet high. The most recent Tsunami occurred on December 26, 2004 in the Indian Ocean. An underwater earthquake measuring 9.0 on the Richter scale caused it. It devastated eleven countries and killed hundreds of thousands of people.


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.