Substitute Lesson Plan: Tides & Currents: Motion in the Ocean

Subject: Earth Science | Grade Level: 9–12 | Duration: ~45 minutes

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Objective

By the end of class, students will be able to:

• Identify the primary causes of ocean currents and waves (wind speed, duration, and fetch).
• Explain how ocean currents vary at different latitudes.
• Explain the cause of the Coriolis Effect and how it influences ocean currents.
• Calculate the magnitude of ocean currents using data from drifter studies.

Materials

• This resource: "Motion in the Ocean" Student Worksheet – "Problems on Winds, Waves, and Currents" (one copy per student or student group)
• Copies of the Currents Subject Review (if students have not already completed it — see note in Warm-up)
• Sverdrup-Munk-Bretschneider Nomogram (Figure 1, included in worksheet)
• Computers with internet access (optional, if students need to reference the Currents Tutorial)
• Pencils/paper

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Warm-up (~5 min)

1. Write on the board: "Why does marine navigation still matter today, even with air travel and modern technology?"
2. Ask students to briefly share ideas. Guide discussion toward the fact that most cargo shipped to and from the U.S. is transported by water, and that safe navigation requires accurate, real-time information about weather and sea conditions.
3. Ask students to brainstorm aloud: What kinds of information would a mariner need to navigate safely? (water levels, currents, tides, weather)
4. Tell students: "Today we're going to learn some basic facts about ocean motion and use that information to solve real problems dealing with winds, waves, and currents."

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Main Activity (~25 min)

1. Distribute the worksheet "Problems on Winds, Waves, and Currents" to each student or student group.

1. Explain the nomogram (5 min): Point out to students that surface ocean waves are produced by wind, and that wave height depends on three factors:
2. Wind speed
3. Duration (how long the wind blows)
4. Fetch (the distance over which the wind blows)

Show students Figure 1, the Sverdrup-Munk-Bretschneider Nomogram, included on their worksheet. Explain that the y-axis shows Wind Speed, the x-axis shows Fetch Length, and the curved lines in the middle show Wave Height in feet.

1. Students work independently or in groups (20 min) to answer the worksheet questions, which include:
2. Using the nomogram to calculate wave height from given wind speed and fetch.
3. Comparing the effects of increasing wind speed vs. increasing fetch length.
4. Calculating current speed and direction from drifter distance/time data.
5. Calculating the magnitude of Coriolis acceleration at different latitudes (e.g., the equator and Tijuana).

1. Circulate the room while students work, reminding them to carefully match the wind speed, fetch, and wave height lines on the nomogram, and to show their work for the current-speed calculations (distance ÷ time).

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Wrap-up / Exit Ticket (~10 min)

1. Lead a class discussion reviewing the correct answers to the worksheet:
2. Q1: 3 feet
3. Q2: Increasing wind speed by 60 knots increases wave height to ~12 feet; increasing fetch by 60 nm increases wave height to less than 6 feet.
4. Q3: A 60-knot wind blowing over a fetch of about 9 miles produces a 10-foot wave.
5. Q4: Current speed ≈ 3.40 knots, direction northeast.
6. Q5: Current speed ≈ 118.4 cm/sec, direction slightly east of due south.
7. Q6: At the equator, Coriolis acceleration is zero (since latitude = 0).
8. Q7: At Tijuana's latitude (~32.5° N), Coriolis acceleration is very small (0.081 cm/sec²).
9. Q8: Even though Coriolis acceleration is negligible on small objects like soccer balls, it becomes significant when acting on very large masses (like ocean currents) over long distances.

1. Exit Ticket: On a slip of paper, have each student answer in 2–3 sentences: "Why is the Coriolis Effect negligible for something small like a soccer ball, but significant for ocean currents?" Collect on the way out.

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If Time Remains

Have students write a short paragraph response to The "Me" Connection prompt from the resource: "How does the Coriolis force affect you personally, even though it is only significant at very large scales?" Students can share their answers aloud if time allows.