How Does the Ocean Change Our Coastline?

Lesson Adapted from: Center for Marine Conservation. (1989). The Ocean Book. New York: John Wiley & Sons, Inc. (ISBN 0-471-62078-5)

Materials Needed

--Dish pan

--Board

--Soil

--Water

Teacher Preparation

Put board in pan about 5" from one end. The board should be about as high as the rim of the pan. Fill 5" side with soil and wet it until it is paste-like mud. Tap it down solidly and let it dry for a few days.

After the soil has dried, put 2" of sand in the pan on the other side of the board. Add about 1 1/2" of water above the sand. Remove the boards. Move the board back and forth in the water until you make small waves. Observe the waves as they erode the soil.

Allow students to have an opportunity to make waves themselves. Have them place barriers, such as pencils, erasers, fingers, etc. in the water to try to prevent soil erosion from happening. Let them be create. Possibly have them experiment for about 10-15 minutes.

Questions for Students to Consider

--What happened to the sand as the water washed against one side of it?

--What relationship does this have to what happens to the beach?

--Does the sand on the beach also shift? (Perhaps some students have built a sand castle and watched the waves remove it.)

--Do larger waves make the sand move farther?

--How do you think the incoming tide affects the movement of the sand?

--Which method that you employed seemed to prevent or slow down soil erosion? Why?

 

Explanation of the Experiment

As energy of the waves is dissipated on the shore, the land is loping beach. The reason the waves break is that the drag of the wave motion, as it reaches shallow water, causes the wave to tumble over itself, much as a person ice skating would fall forward when skating off the ice onto dry ground.

As an additional experiment to show that waves do not move water as they travel across the sea, put a small cork on the surface of the water and create waves gently by moving the board as before. Notice that the cork does not move forward as the wave advances. Instead it merely moves up and down or actually in a circular manner as the waves pass by. Thus, waves do not move water across the sea. They are only a surface phenomena, and it is only when the waves break on the shore that the water particles move back and forth.

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