L5th - The Oceans

The Oceans

Science ‐ Lower 5th Grade St. George's College October, 2008 1

Brainstorming: What is the Connection between Oceans and Climate?

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Objectives • • • • • •

Explain the Desalination process.

Define and describe the processes involved in the Water Cycle.

Describe the composition of Ocean Water.

Explain the formation of Ocean Currents.

Compare and contrast waves, tides, and currents.

Explain what causes tides to rise and fall.

Note: Most of the objectives will be covered in class, however the student must be responsible for those objectives not covered or concluded.

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Vocabulary Water cycle: the constant recycling of water on Earth.

Evaporation: the process in which a liquid changes to a gas.

Condensation: the process by which water vapor changes from a gas to a liquid.

Precipitation: water that falls to Earth as rain, snow, sleet, or hail.

Wave: an up‐and‐down movement of water.

Storm surge: a very large series of waves caused by high winds over a large area of ocean.

Tide: the daily changes in the local water level of the ocean.

Surface current: an ocean current formed when steady winds blow over the surface of the ocean.

Deep ocean current: an ocean current formed when cold water flows underneath warm water.

Note: Most of the vocabulary words will be covered in class, however the student must be responsible for those words not covered or concluded.

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Lesson 1: What role do Oceans play in the Water Cycle?

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The Water Cycle • Oceans cover more of Earth's surface than dry land does. Even though ocean water is salty, it provides a large amount of Earth's fresh water. earth's water is always being recycled, this is called the water cycle.

• During the cycle, water changes from a liquid to a gas and back to a liquid.

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What is in Ocean Water • Ocean water is a mixture of water and many dissolved solids. Most of these solids are salts. Sodium chloride is the most common salt in ocean water.

• Most of the salts and other substances in the ocean come from the land. As rivers, streams, and runoff flow over the land, they slowly break down the rocks that make it up.

• Over time, flowing water carries substances from the rocks to the ocean.

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Lesson 2: What are the Motions of Oceans?

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Waves

• A wave is the up‐and‐down movement of the water particles in the ocean.

• Water waves are caused by the wind. As wind blows over the water surface, it pulls on the water particles. This causes small bumps, or ripples, of water to form. As the wind continues to blow, the ripples keep growing. Over time they become waves.

• The height of a wave depends on 3 things: the strength of the wind, the amount of time the wind blows, and the size of the area over which the wind blows.

• Waves change the shore in different ways. When waves break on a beach, water carries sand and other sediments as it flows back into the ocean.

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Tides • Another type of ocean water motion is called tides. Tides are the daily changes in the local water level of the ocean.

• At high tide much of the beach is covered by water. At low tide waves break farther away from shore. Less of the beach is under water. High tide and low tide are usually a little more than six hours apart.

• Tides are caused by gravity. Gravity is a force that causes all objects to be pulled toward all other objects.

• The force of gravity between two objects depends on two things: the sizes of the objects and the distance between them.

• Even though the moon is much smaller than the sun, the pull of the moon's gravity on Earth is the main cause of ocean tides. This is because the moon is much closer to earth than the sun is.

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Currents • Currents are rivers of water that flow in the ocean. A surface current forms when steady winds blow over the surface of the ocean.

• In the Northern hemisphere, surface currents flow in a clockwise direction.

• In the Southern hemisphere, surface currents flow in a counterclockwise direction.

• Deep ocean currents form because of density differences in ocean water. The density of ocean water depends on two things: the amount of salt in the water and the temperature of the water.

• The more salt there is in water, the denser it will be. Cold ocean water also is denser than warm ocean water.

• Deep ocean currents form when dense, cold water meets less dense water.

• The denser water flows under the less dense water, forcing the less dense water to rise.

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