What is a watt?

Watt (named in honor of James Watt) is the practical electrical unit of activity or rate of doing work. It is measured by the product of the voltage or electromotive forcé of the source into the current supplied. Thus a dynamo which is yielding 30 amperes at a voltage of 100 is working with an activity of 3,000 watts. The watt is equal to 0.735 foot-pound per second; so that one horse power per second is equal to 746 watts. It is customary to use the kilowatt, equal to 1,000 watts.

How do we measure energy?

We measure energy by the amount of work it does. We measure it in foot-pounds. For example, 20 foot-pounds is the amount of energy it would take to lift 2 pounds 10 feet, or 10 pounds 2 feet, or 5 pounds 4 feet. We also measure energy in cal¬ories. A "small calorie," the kind people count when they are dieting, is a thousand times bigger — so a man on a strict diet might eat only enough food to give him 3,000,000 foot-pounds of energy a day. We also measure energy in joules, ergs, horsepower-hours, kilowatt-hours, and all sorts of units, depending on the kind of work we mean.

Natural gas

When white men first explored the Appalachian Mountains, their Indian guides had a strange sight to show them. In places there were fires that burned day and night on bare slopes where there seemed to be nothing to burn. No wonder the Indians thought the fires were mysterious! The fuel that was burning was one that no one can see. It was natural gas.
More than 150 years ago the people of a small city in western New York discovered natural gas coming out of cracks in the rock along the banks of a nearby creek. Some of the people piped the gas into their houses and burned it for light. The idea spread. A German scientist who saw gas lights in America called them the eighth wonder of the world.
Soon afterward, when people began to dig wells to get oil, natural gas came from many of the wells. It was a nuisance. Sometimes it caused explosions. Sometimes it caught on fire and set fire to the oil. To get rid of it, the oilmen piped it away and burned it.
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Where the energy begins

Hoover Dam is only one of the big dams in the United States. It is on the Arizona-Nevada border. Day and night the wheels turn around to supply us with electric energy.
As you can see, rivers and other bodies of water have a great deal of energy. Where did all this energy begin? What happens when the Sun shines on a puddle? Heat from the Sun changes the water to water vapor. The water vapor goes into the air. Some of it goes up high ano! forms clouds.
Raindrops fall from the clouds. Gravity pulls them down to the Earth. The water keeps falling downward from high places. Rivers flow downhill. Water rushes over cliffs and dams. Gravity makes the water flow from high places to low. This goes on year after year.
All the energy from moving water depends on the Sun. If the Sun stopped shining, no clouds would form, no rain would fall. There would be no way that water could get uphill for gravity to pull it downhill again. There would be no more energy from rivers and waterfalls.
But the Sun does shine. The rain falls. The rivers flow. Water does keep moving. We can keep using the energy from moving water.

Hydroelectric power in the United States

Hydroelectric Power 
   Electricity generated by moving water from dams is called hydroelectric power. The sun provides heat energy that evaporates surface water from oceans, lakes, and streams. The water returns to the earth as rain or snow. Reservoirs behind dams built across river valleys collect and store the water.
The mechanical energy of the moving water as it leaves the dam is converted to electricity. The amount of kinetic energy in the falling water depends on the speed and the volume of the water available to turn the generators. About 10 percent of the electricity used in the United States is produced by hydroelectric power.
Generating electricity with water power is efficient and clean. Little energy is lost, and no pollutants are produced. Another advantage of hydroelectric power is its low cost. Although dams are expensive to build, hydroelectric plants have low operating costs.
   The lakes, or reservoirs, behind the dams also provide water storage for irrigation and serve as recreational areas. However, building a dam changes a river forever. It floods low-lying areas upstream, destroying farmland and wildlife habitats. Dams may also block the migration and survival of some kinds of fish, such as salmon.