Roberta A. Mazzucco
Water power provides only a small per cent of the world's energy. Obviously, only at places where there is water flowing downhill can that energy be captured and utilized to do some sort of work. Falling water is mostly used to produce electricity. There is a short film on YouTube
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:. It shows how turbines are constructed at the base of the dam, so that the force of the falling water will make it turn and begin the process of generating electricity.
Dams have long been a source of water for people, animals, and the irrigation of crops. The real innovation came when they were used to produce electricity. There are 45,000 dams in the world with a vertical distance of 50 feet or more. The aggressive building of dams for electrical power in the United States began in the 1930s when the Hoover Dam was built. It was part of the government's attempt to jump start the economy during the Great Depression. This period of dam building ended in 1962 with the completion of the Glen Canyon Dam. While it was generally acknowledged that these dams were positive developments, during this time the first environmental group began namely, The Sierra Club. It was begun by the naturalist John Muir, who wanted the Sierra Nevada Mountains to remain in as pristine condition as possible. By the time the Glen Canyon Dam was started, there was already agreement that that would be the last project undertaken.
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At this point, hydropower in the form of large dams has reached its limit in the United States and so it is not a potential for expansion. South America and Asia still have some potential for hydropower development. However, environmentalists now regard these projects as serious intrusions into the natural and they are prepared to block the building of any large dams.
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The teaching objective would be for students to see that falling water offers another possibility for energy to be produced. It would also be a good chance to do research on dams and how they work. Again, students will see that running water has the potential to do a lot of work. However, they will still see that a flowing river is not available in all areas. It not a complete answer to our energy needs.
The activity that I suggest for hydropower is for students to see how the weight of the water works to produce the force necessary to complete work.
Activity 4: Hydro Power
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Materials: Half gallon paper milk carton (empty and washed out), a gallon of water, an awl, or 10p nail, masking tape, ruler, magic marker, scissors, pad and paper to make notes
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1. Cut off the top of the milk carton
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2. Measure from the bottom of the carton and put a hole in the side of the carton at the half inch, inch, 2 inch and 4 inch mark. (All holes should be the same size)
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3. Take along piece of tape and tape up the holes. Mark a line near the top of the carton. Always refill the container to that line.
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4. Fill the container with water. Have the container on the edge of a sink. Quickly take off the tape and watch what happens. Measure how far away each of the streams hits the sink.
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5. Watch as all the water empties out. What happens as the water level drops. What happens to the stress of water?
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6. Tape up the holes again and refill the carton. This time uncover just the bottom hole. Refill the container and cover the holes again; repeat with the second hole form the bottom -- measuring how far the stream goes. Do this for the other 2 holes.
Through this experiment students will find that the hole on the bottom had the longest stream of water. Water has weight and that weight of water exerts a force or pressure from above. The greater the weight of the water is the greater the resulting water pressure. The more water pressure, the further out the stream went.
As was stated earlier, hydroelectric plants are built at the base of dams so that they can utilize this high pressure of the falling water.