Tides and Currents: Motion in the Ocean

By NOAA

What This Lesson Is About

This lesson helps older students learn what makes ocean currents (moving streams of water in the ocean) and waves happen. It also teaches about something called the Coriolis Effect, which is a force caused by Earth spinning that bends the path of moving water and air.

Why This Matters

Almost all the goods that come in and out of the United States travel by ship. That means people who work on ships need good, up-to-date information about the weather and the water. Ocean conditions can change fast and be very different from place to place. If sailors don't have good information, ships could crash or get stuck.

NOAA has a special group called CO-OPS. This group collects information about water levels, currents, and tides (the rise and fall of the ocean, caused mostly by the pull of the moon). CO-OPS does these jobs:

• Shares information about water levels, currents, and tides
• Sets rules for how to collect this information correctly
• Studies new tools for measuring the ocean
• Builds computer programs to handle ocean data
• Checks that the data is correct
• Shares this information with everyone

CO-OPS also runs a system called PORTS®, found in big harbors across the country. PORTS® gives sailors real-time facts, like water levels, currents, weather, and the "air gap" — the space between the water and the bottom of a bridge. This helps ships avoid crashing into bridges or running aground.

CO-OPS mostly studies water near the coast. Other parts of NOAA study currents out in the open ocean. One group, called NODC, collects information from tools like current meters and floating drifters that measure how water moves. Another NOAA website, called OSCAR, uses satellites to track currents all over the world.

What Students Will Do

In this lesson, students will look at how currents, wind, and ocean waves are connected.

Steps for the Lesson

1. The teacher will look over some background readings and a worksheet about winds, waves, and currents before class.

1. The teacher will ask students why ocean travel still matters today, even though we have airplanes. Students will talk about how oceans are still important for moving goods, making energy, and having fun. They will also talk about why real-time information helps keep sailors safe.

1. Students will read a short lesson called the Currents Subject Review and answer questions about it. This can be done alone or in groups.

1. Students will complete a worksheet called "Problems on Winds, Waves, and Currents."

1. The class will go over the answers together. The teacher will make sure everyone understands how wind, waves, and currents are all connected.

Answer Key (for the Worksheet)

1. The wave would be about 3 feet tall.
2. Making the wind blow harder (60 knots faster) would make bigger waves — about 12 feet tall. Making the fetch (the distance wind blows over water) 60 nautical miles longer would only make waves less than 6 feet tall. So, faster wind makes a bigger difference.
3. A 60-knot wind would need to blow over about 9 miles of open water to make a 10-foot wave.
4. Using math with distance and time, the current speed comes out to about 3.40 knots, moving toward the northeast.
5. Using different units (centimeters and seconds), the current speed comes out to about 118.4 centimeters per second, moving slightly east of south.
6. At the equator (the imaginary line around the middle of the Earth), the Coriolis force is zero. That's because of the math behind how this force works.
7. Near Tijuana, the Coriolls force is very small — only about 0.081 centimeters per second squared. That's a tiny amount!
8. Even though the Coriolis force is too small to notice on things like soccer balls or people walking, it becomes powerful when it acts on huge things — like the entire ocean — moving over very long distances.

Extra Activity: "The Me Connection"

Have students write a short paper about how the Coriolis force affects them personally — even though the force is too small to feel or notice in everyday life.

How Students Will Be Graded

Students will complete the worksheet to show what they learned.

Want to Learn More?

• Visit NOAA's "Tides and Water Levels" website for more lessons and activities.
• Visit the University of Southern Maine's Osher Map Library website for more lesson plans about currents.
• Visit an online learning site with interactive lessons about ocean currents and waves — including one activity about landing a plane on an aircraft carrier while accounting for the Coriolis Effect!

What Students Will Need

• A copy of the "Problems on Winds, Waves, and Currents" worksheet
• A copy of the Currents Subject Review
• A computer with internet access

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Student Worksheet: Problems on Winds, Waves, and Currents

Waves in the ocean are made by wind. How tall a wave gets depends on three things:

• How fast the wind blows (wind speed)
• How long the wind blows (duration)
• How far the wind blows over open water (fetch)

In 1952, a scientist named Charles Bretschneider made a special chart to show how these three things work together. This chart helps people guess how tall a wave will be based on the wind. Look at Figure 1 below. It shows:

• Wind Speed going up the side
• Fetch Length going across the bottom
• Wave Height shown by curved lines in the middle

Figure 1: Sverdrup-Munk-Bretschneider Chart

Question 1: If wind blows over a 10 nautical mile stretch of water at 21 knots, how tall would the wave be?

Question 2: What would make waves grow taller more — a stronger wind, or a longer fetch? Use the chart to compare.