Tides and Currents: Motion in the Ocean

Author: NOAA
Grade Level: 9–12
Subject Area: Earth Science

Resources

• A lesson on the Coriolis force (the effect that makes moving air and water curve because Earth is spinning) from NOAA's Ocean Explorer program, including "the Dishpan Analogy" explanation.
• A tutorial on tidal, coastal, and ocean currents.
• NOAA's "Tides and Water Levels" tutorial.
• NOAA's Center for Operational Oceanographic Products and Services (CO-OPS) website, with data and information about tides, water levels, currents, predictions, weather, forecasts, and other measurements.
• Lesson plans and activities about currents from the University of Southern Maine's Osher Map Library.
• An online tutorial with more details about ocean currents.

Standards Addressed

National Science Education Standards

Content Standard A: Science as Inquiry

• Skills needed to do scientific investigations
• Understanding what scientific inquiry involves

Content Standard B: Physical Science

• Motion and forces

Content Standard D: Earth and Space Science

• Energy in the Earth system

Content Standard E: Science and Technology

• Skills used in designing technology
• Understanding science and technology

Content Standard F: Science in Personal and Social Perspectives

• Natural resources
• Environmental quality
• Natural and human-caused hazards
• Science and technology in local, national, and global challenges

Time Required

One 45-minute class period, plus extra time for student research.

Lesson Goal

Students will explore what causes ocean currents and waves.

Learning Objectives

By the end of this lesson, students will be able to:

• Identify the main causes of ocean currents and waves.
• Explain how and why ocean currents change depending on latitude (how far north or south a location is from the equator).
• Explain what causes the Coriolis Effect and how it influences ocean currents.
• Calculate the size (magnitude) of ocean currents using data from drifter studies (studies that track floating devices carried by currents).

Background Knowledge

More than 98% of all cargo shipped into and out of the United States travels by water. To keep ships moving safely and efficiently along the coast, sailors need more than just accurate maps — they also need up-to-the-minute information about weather and sea conditions. Because these conditions can change quickly and vary a lot from place to place, mariners (people who navigate ships) rely on real-time data to avoid running aground or crashing into other vessels.

NOAA's Center for Operational Oceanographic Products and Services (CO-OPS) collects and shares information about oceans to help keep sea travel safe, efficient, and environmentally friendly. This center:

• Provides information on water levels, coastal currents, and tides.
• Sets standards for how this data should be collected and processed.
• Researches new or improved ways to observe ocean conditions.
• Designs software to better process data.
• Regularly checks and reviews data for accuracy.
• Shares this information with the public.

CO-OPS also runs a nationwide system called the Physical Oceanographic Real-Time Systems (PORTS®), located in major U.S. harbors. PORTS® gives sailors real-time information such as water levels, currents, "air gap" (the space between the water's surface and the bottom of a bridge), weather data, and other useful ocean information — all to help avoid accidents.

While CO-OPS focuses mainly on currents near coastlines and inside bays, other parts of NOAA study currents and circulation patterns out in the open ocean. NOAA's National Oceanographic Data Center (NODC) gathers information from the newest current-measuring programs, which use tools like current meters and floating drifters. Through NODC's website, you can find data sets covering topics like beach temperatures, coastal buoy readings, global temperature and salinity levels, and even photo collections. For current data gathered by satellites, you can visit NOAA's Ocean Surface Current Analyses website.

In this lesson, students will explore how currents, winds, and ocean waves are all connected.

Procedures / Teaching Steps

1. Preparation: Before teaching this lesson, review the following:

• Introductory materials on tides and currents.
• The Currents Subject Review (a printable handout is available).
• The "Problems on Winds, Waves, and Currents" worksheet (also available as a printable handout).
• You may also want to look at the "Tides and Water Levels" tutorial, which explains the systems that control tides and water levels, points you toward useful data, and includes lesson plans for grades 9–12.

2. Class Discussion: Ask students why marine navigation still matters today. Even though air travel and space technology have advanced a lot, the ocean is still essential for shipping goods, producing energy, and recreation. Talk about why real-time information is important for safe navigation, and have students brainstorm what kinds of information a sailor today would find useful. Explain that their assignment is to learn some basic facts about "ocean motion" and use that knowledge to solve problems about winds, waves, and currents.

3. Subject Review: If they haven't already, have students complete the Currents Subject Review. You can have students work in groups, with different students or groups covering different sections of the tutorial. Each student or group should answer the review questions. If students don't have internet access, print copies of the tutorial for them. This step can also be assigned as homework to save class time. Afterward, discuss the answers as a class, pointing out ways that understanding tides can be useful in real life.

4. Worksheet: Give each student or group a copy of the "Problems on Winds, Waves, and Currents" worksheet, and have them work through the questions.

5. Discussion: Go over the worksheet answers as a class. Make sure students understand how winds, ocean waves, and currents are all related.

Correct Answers:

1. 3 feet
2. Increasing the wind speed by 60 knots would raise the wave height to about 12 feet, while increasing the fetch (the distance the wind blows over water) by 60 nautical miles would raise the wave height to less than 6 feet.
3. A 60-knot wind would need to blow over a fetch of about 9 miles to create a 10-foot wave.
4. The distance between the two points is 524.6 nautical miles. The total time that passed was 6 days and 10.25 hours, which equals 154.25 hours. So the estimated current speed is:

524.6 nautical miles ÷ 154.25 hours = 3.40 knots
The current is moving toward the northeast.

1. The distance between the two points is 1,443.68 kilometers, which equals 1.444 × 10⁸ centimeters. The total time that passed was 14 days and 2.92 hours, which equals 338.92 hours, or 1.220 × 10⁶ seconds. So the estimated current speed is:

1.444 × 10⁸ cm ÷ 1.220 × 10⁶ sec = 118.4 cm/sec
The current is moving slightly east of due south.

1. Since the latitude at the equator is zero, the formula for Coriolis acceleration shows that this acceleration is zero right at the equator.
2. Tijuana's latitude is about 32.5° N. A speed of 10 meters per second equals 1,000 centimeters per second. So the Coriolis acceleration is:

(sin 32.5° × 1.5 × 10⁻⁴ × 1,000) cm/sec²
= 0.537 × 1.5 × 10⁻⁴ × 1,000 = 0.081 cm/sec²
This effect is very small.

1. Even though the Coriolis effect barely affects small things like soccer balls or walking people, when it acts on huge masses of water or air over very long distances, its effect becomes significant.

The Bridge Connection

The Bridge is a growing online collection of marine education resources. It gives teachers an easy way to find reliable information on marine science topics at the global, national, and regional levels. Educators and scientists check each resource on the Bridge to make sure it is accurate and up to date. On the website, click "Ocean Science Topics," then "Physics," then choose a heading at the top of the page to find links and resources about tides, waves, and currents.

The "Me" Connection

Have students write a short essay about how the Coriolis force affects them personally — even though its effects are usually too small to notice, except over very large scales.

Outcome / Assessment

Students will complete the worksheet.

Extensions

1. Visit the "Tides and Water Levels" Discovery Kit for more resources and lesson plans.
2. Visit the University of Southern Maine's Osher Map Library website for more lesson plans and activities about currents.
3. Visit the Multimedia Learning Objects website and look for Lessons 8 and 9. These include interactive presentations and activities on Ocean Currents and Ocean Waves — including one where you have to safely land a plane on an aircraft carrier by accounting for the Coriolis Effect.

Classroom Resources

Materials for Students:

• Copies of the "Problems on Winds, Waves, and Currents" worksheet — one per student or group.
• Copies of the Currents Subject Review.
• Computers with internet access.

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Motion in the Ocean

Student Worksheet — Problems on Winds, Waves, and Currents

Surface ocean waves are created by wind. The height of these waves depends on three things: wind speed, how long the wind blows (duration), and the distance over which the wind blows across open water (fetch).

In 1952, a scientist named Charles Bretschneider created a diagram showing how these three factors relate to each other. This diagram makes it easy to predict how tall a wave will be under certain wind conditions. Figure 1 shows an example of this kind of diagram, called a "Sverdrup-Munk-Bretschneider nomogram."

On the diagram, the y-axis (vertical) shows Wind Speed. The x-axis (horizontal) shows Fetch Length. The curved lines in the middle show Wave Height in feet. (Many versions of this diagram also include lines for wave period and wind duration, but those have been left out of Figure 1 to keep it simple.) Be careful to match each curved line with its correct label when reading the diagram!

Figure 1: Sverdrup-Munk-Bretschneider Nomogram

1. If wind blows across a 10-nautical-mile fetch at 21 knots, what would the resulting wave height be?

1. What would cause a bigger increase in wave height for the conditions in the question above — [text continues in original source]