Ups and Downs

What Causes Tides / Grades 9-12 / Earth Science




Focus Question

What causes tides and tidal currents?

Learning Objectives

Links to Overview Essays and Resources Useful for Student Research

http://oceanservice.noaa.gov/education/tutorial_tides - Tides and Water Levels Tutorial and Subject Review

http://www.edusite.com/sci/tides.htm – Links to Internet sites with information about tides

Materials

Audio/Visual Materials

Teaching Time

Seating Arrangement

Maximum Number of Students

32

Key Words

Tide
Tidal current
Ebb
Flood
Spring tide
Neap tide
Perihelion
Aphelion
Perigee
Apogee
Lunar cycle

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Background Information

Tides are the periodic rising and falling of ocean waters caused by the gravitational forces of the sun and moon. The vertical motion of tides is accompanied by a horizontal movement of ocean waters called tidal currents. Oceanographers say that tides rise and fall, while tidal currents ebb (during a falling tide) and flood (during a rising tide).

For a simple explanation of tides, it is sufficient to consider only the effects of the moon (the magnitude of the moon's effect is about twice that of the sun, since the moon is closer to the Earth). At any point in a day, one side of the Earth will be closer to the moon than the opposite side. Ocean waters on the closer side of the Earth will experience a greater gravitational pull from the moon than waters on the opposite side of the earth (tide generating forces vary inversely as the cube of the distance from the tide generating object). This causes a "bulge" in the waters closest to the moon, and creates a high tide. At the same time, inertial forces on the opposite side of the Earth causes a similar "bulge" creating another high tide. Low tides occur at longitudes that are 90° from the longitudes of locations that are experiencing high tides. The sun also exerts a gravitational force on ocean waters. Depending upon the positions of the sun and moon relative to the Earth, the sun's gravity may enhance or diminish the tidal effect caused by the moon. When the sun and moon are aligned (at the time of full moon or new moon), their gravitational forces act in the same direction and produce more pronounced high and low tides that are called spring tides. When the sun and moon are at right angles relative to the earth, the gravitational force of the sun partially cancels out the gravitational force of the moon. The result is less pronounced high and low tides that are called neap tides. The magnitude of tides is also affected by the actual distances between the sun, moon, and Earth: Gravitational attraction is increased when the Earth is closest to the sun (perihelion) or moon (perigee). For more information on the causes and types of tides, visit: http://oceanservice.noaa.gov/education/tutorial_tides

For centuries, people who live and work near seacoasts have understood the importance of being able to predict tides and tidal currents. Low tides may prevent ships from entering harbors, while high tides may make it impossible for ships to pass beneath bridges. Tidal currents may significantly increase the speed of a vessel, or may carry it into dangerous waters. Recreational boaters who anchor near shore may find themselves stranded by a falling tide. Fishermen throughout the world have learned that catches are likely to be much larger during certain portions of the tidal cycle than others.

Many people who live thousands of miles from any ocean also pay close attention to the same lunar cycles that produce tides. Traditional agricultural practices often prescribe planting and harvesting during times when the moon is at a specific location relative to the Earth. Some traditional forestry practices link lunar cycles with specific properties of wood including strength, resistance to decay, and resonance for musical instruments. Lunar cycles have also been linked with many aspects of human biology, behavior, and folklore including crime, suicide, mental illness, birthrates, fertility, werewolves, and vampirism. The first part of this lesson is intended to:

In the second part of this lesson, students will design and prepare educational materials that can be used to explain the fundamental tidal phenomenon as part of introductory middle school oceanography lessons.

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Learning Procedure

[Note: This lesson is based, in part, on an activity created by Claire Silva, Biology Teacher]

Part 1: Researching and Exploring Tides

  1. Direct students to the Tides and Water Levels Tutorial and the Tides Subject Review at: http://oceanservice.noaa.gov/education/tutorial_tides. If you choose to have students work in groups, you may want to assign different tutorial sections to each student. Have each student or student group answer questions in the Tides Subject Review. To save class time, you may want to assign this portion of the lesson as homework.
  2. Review students' answers to questions in the Tides Subject Review. Lead a brief discussion of ways in which knowledge of tides can be useful and important.
  3. Have each student or student group answer questions on the "Student Worksheet" using data from http://tidesonline.nos.noaa.gov or from Appendices A, B1, B2, C1, and C2.

Part 2: Explaining Tidal Phenomena

Have students or student groups prepare visual materials that could be used to explain tides and tidal currents to a 5th or 6th grade science class. Appropriate materials may include physical models (e.g., mobiles), visual media (e.g., Powerpoint® presentations; computer animations), theatrical presentations (e.g., drama; music; dance), or publications. Materials produced should support explanations about:

Encourage (and give credit for) creativity! These presentations offer cross-curricular opportunities, particularly with social studies, English language arts, and fine arts. Whatever media students choose to work with, their final presentation should be accompanied by a list of sources for the information they present. A good starting point for this activity is the Roadmap to Resources: Tides & Water Levels (http://oceanservice.noaa.gov/education/tutorial_tides/supp_tides_roadmap.html), which provides links to many other sources of data and information about tides.

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The Bridge Connection

The Bridge is a growing collection online marine education resources. It provides educators with a convenient source of useful information on global, national, and regional marine science topics. Educators and scientists review sites selected for the Bridge to insure that they are accurate and current.

www.vims.edu/bridge - Click on "Ocean Science Topics" in the navigation menu to the left, then "Physics." There are many resources on tides and currents in these pages.

The “Me” Connection

Have students write a short essay on why knowledge about tides and water levels is (or might be) important in their own lives.

Extensions

The rise and fall of ocean tides involve huge amounts of energy. Have students or student groups prepare a report on how this energy could be captured in a form that could be used by humans. Reports should include a plausible mechanism for converting tidal motion into useful energy, a strategy for transporting captured energy to potential users, and a rough estimate of the energy that might be available from tidal sources. A keyword search on "tide energy" will produce lots of starting points.

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Resources

http://oceanservice.noaa.gov/education/tutorial_tides/supp_tides_roadmap.html – NOAA's National Ocean Service Web site's Roadmap to Resources about tides and water levels, with links to many other sources of tide data and background information

http://www.navmetoccom.navy.mil – Naval Meteorology and Oceanography Command Web site with information on waves and tides and other oceanography topics

http://www.edusite.com/sci/tides.htm – Links to educational resources on ocean science topics

http://www.internet4classrooms.com/tide.htm – Links to internet resources dealing with tides

http://school.discovery.com/curriculumcenter/oceans – Discovery Channel School resources on ocean science topics

National Science Education Standards

Content Standard A: Science as Inquiry

Content Standard B: Physical Science

Content Standard D: Earth and Space Science

Content Standard E: Science and Technology

Content Standard F: Science in Personal and Social Perspectives

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Ocean Literacy Essential Principles and Fundamental Concepts

Essential Principle 1. The Earth has one big ocean with many features.

Essential Principle 6. The ocean and humans are inextricably interconnected.

Essential Principle 7. The ocean is largely unexplored.

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Ups and Downs

Student Worksheet - Analyzing Real-time Water Level Data from Monitoring Stations

NOAA Tides and Currents, managed by the Center for Operational Oceanographic Products and Services (CO-OPS), provides access to NOAA's vast collection of oceanographic and meteorological data (historical and real-time), predictions, and "nowcasts" and forecasts. Tides Online provides an easy way to view recent data from the National Water Level Observation Network, a network of 175 continuously operating water-level stations throughout the USA.

  1. Open the Tides Online Web page at http://tidesonline.nos.noaa.gov/. Click "State Maps," then on "MA" (Massachusetts) and select "Woods Hole." If at any point there are no data available, hypothesize on what might have caused this error. Is there unusual or severe weather at the monitoring station?
  2. How many high and low tides did Woods Hole, MA experience in the last lunar day? What type of tidal pattern did Woods Hole experience? What are the tidal heights in Woods Hole, MA?
  3. How do the observed and predicted data compare? What may have caused any differences between the observed and predicted data for Woods Hole, MA?
  4. Click the Back button twice on your browser or return to http://tidesonline.noaa.gov/geographic.html. "Click" on AL (Alabama) and select Dauphin Island, AL.
  5. How many high and low tides did Dauphin Island, AL experience in the last lunar day? What type of tidal pattern did Mobile experience? What are the tidal heights in Dauphin Island, AL?
  6. How do the observed and predicted data compare? What may have caused any differences between the observed and predicted data for Dauphin Island, AL?
  7. Click the Back button twice on your browser or return to: http://tidesonline.noaa.gov/geographic.html. "Click" on WA (Washington) and select Seattle, WA.
  8. How many high and low tides did Seattle, WA experience in the last lunar day? What type of tidal pattern did Seattle experience? What are the tidal heights in Seattle, WA?
  9. How do the observed and predicted data compare? What may have caused any differences between the observed and predicted data for Seattle, WA?

Conclusion questions:

  1. Summarize what causes tides. Discuss the effects of tidal forces and how bulges are formed.
  2. Explain why humans are interested in monitoring tides. What impact do tides have on human life? What impact might tides have on other organisms?
  3. Discuss how tides are monitored. Describe the old and new methods of monitoring tides.
  4. Compare and contrast the tidal patterns of Cape Cod, MA, Dauphin Island, AL, and Seattle, WA. What is the tidal pattern in your area?

Further Exploration:

Using the NOS Web site at http://tidesonline.nos.noaa.gov/geographic.html, select a tidal gauge that is located near your area. Monitor the tidal gauge for one month and record tidal fluctuations. Note any deviation from the predicted and observed tidal levels. What do you think causes this deviation?

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Appendix A

Water Level and Temperature Data for Monitoring station # 8447930, Woods Hole, MA


Appendix A


Click here for a printable version of this page


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Appendix B (pt. 1)

Water Level and Wind Data for Monitoring station #8735180 Dauphin Island , AL


Appendix B


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Appendix B (pt. 2)

Air Pressure and Temperature Data for Monitoring station #8735180 Dauphin Island, AL


Appendix B


Click here for a printable version of this page


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Appendix C (pt. 1)

Water Level and Wind Data for Monitoring station # 9447130 Seattle, WA


Appendix C


Click here for a printable version of this page


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Appendix C (pt. 2)

Air Pressure and Temperature Data for Monitoring station # 9447130 Seattle, WA


Appendix C


Click here for a printable version of this page


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