Tides, Waves & Currents
Know that tides are regular rises and falls in sea level caused mainly by the Moon's gravity, with the Sun contributing. Many coasts have roughly two high tides per day, while some have one. Wind makes most familiar surface waves. Currents move water and carry heat and nutrients; tides and wind can both drive currents.
What a learner can do afterwards
- Describe tides as the regular rise and fall of sea level, caused mainly by the Moon's gravity with a contribution from the Sun
- Explain that wind blowing across the water makes most familiar surface waves
- Describe ocean currents as large flows of water that carry heat and nutrients around the globe
1 · Read
The ocean never sits still. Water moves in three big ways: tides, waves, and currents. They can overlap, and one can help cause another. Tides are the slow rise and fall of the sea. The Moon's gravity pulls the water while Earth turns, and the Sun pulls a little too. Many coasts get about two high tides a day, and some get only one.
At the beach, Priya feels a strong wind blowing across the water. She watches waves roll in and crash on the sand. The wind is pushing the water into waves.
Ocean currents are like giant rivers flowing inside the ocean. Some carry warm water toward colder places, and some carry cold water toward warmer ones. They also carry nutrients, dissolved food for ocean plants and tiny animals. Wind drives many currents, and rising and falling tides drive others.
A current carries heat from warm seas toward cold ones.
Remember it this way: tides move up and down, wind pushes up most surface waves, and currents flow like rivers across the ocean.
Tides rise and fall mainly from the Moon's pull, wind makes most surface waves, and currents move water, heat and nutrients around the world.
The rewritten readings were written for this dataset.
More to read
Why sea levels rise and fall
At many seaside places, the water rises and falls about twice each day. These changes are tides. People long ago spotted a clue: high tides often happened later each day, much as the Moon rose later. This helped them link tides to the Moon.
The Moon's gravity pulls unevenly on Earth and its water, helping form ocean bulges. Earth's spin carries places through higher and lower water. Many coasts have about two high tides and two low tides daily; others have about one of each. Tide sizes change through the month as the Moon travels around Earth.
Tidal Power
The Moon and the Sun pull on Earth with gravity, and Earth spins around and around. Together, these things make the ocean tides. In some places, the water near the shore rises and falls as much as 40 feet. That is taller than a house. Long ago, people in Europe used the moving tide water to spin mills that ground grain into flour. Today, special machines can use the tides to make electricity. Some of these machines work best where the water rises and falls a long way between high tide and low tide. Others sit in fast tidal currents and use the moving water instead.
Ocean Energy
The ocean is always moving, and all that motion holds energy. Ocean energy is a way of making electricity from sea water. It can use the tides, the waves, or the temperature difference between warm surface water and cold deep water. Most surface waves are made when wind blows across the water. Currents are like rivers flowing through the ocean. Some carry warm water and some carry cold, and they carry dissolved nutrients along with it. This kind of energy is renewable, which means nature keeps making more of it. But it is not easy to use. Most ocean energy machines are still being invented and tested. Scientists are working hard to solve the problems, because the ocean could give us a lot of clean power one day.
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2 · Watch
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Where it sits
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Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.