When you get down to basics, there are only five fundamental sources of energy on the Earth: (1) energy generated by nuclear fusion in the Sun and transported to Earth via electromagnetic radiation; (2) energy generated by the pull of gravity; (3) energy generated by nuclear fission reactions; (4) energy that has been stored in the interior of the Earth since the planet’s beginning; and (5) energy stored in the chemical bonds of compounds. Let’s look at the different ways these forms of energy become resources we can use (_Fig. 1).
• Energy directly from the Sun: Solar energy, resulting from nuclear fusion reactions in the Sun, bathes the Earth’s surface. It may be converted directly into electricity, using solar-energy panels, or it may be used to heat water or warm a house. (No one has yet figured out how to produce controlled nuclear fusion on Earth, but we can produce uncontrolled fusion by exploding a hydrogen bomb.)
• Energy directly from gravity: The gravitational attraction of the Moon, and to a lesser extent the Sun, causes ocean tides, the daily up-and-down movement of the sea surface. The flow of water in and out of channels during tidal changes can drive turbines.
FIGURE 1. The diverse sources of energy on Earth. Solar energy can be used directly, to drive wind or to cause water to evaporate and make rain and ultimately running water. It also provides energy for photosynthesis, which produces wood and plankton; these ultimately become fossil fuels (coal and oil, respectively). Radioactive material from the Earth powers nuclear reactors, and the Earth’s internal heat creates geothermal resources. Gravity plays a role in producing wind and water power.
• Energy involving both solar energy and gravity: Solar radiation heats the air, which becomes buoyant and rises. As this happens, gravity causes cooler air to sink. The resulting air movement, wind, powers sails and windmills. Solar energy also evaporates water, which enters the atmosphere. When the water condenses, it rains and falls on the land, where it accumulates in streams that flow downhill in response to gravity. This moving water powers waterwheels and turbines.
• Energy via photosynthesis: Green plants absorb some of the solar energy that reaches the Earth’s surface. Their green color comes from a pigment called chlorophyll. With the aid of chlorophyll, plants produce sugar through a chemical reaction called photosynthesis. In chemist’s shorthand, we can write this reaction as:
6CO2 + 12H2O + light → 6O2 + C6H12O6 + 6H2O.
Carbon water oxygen sugar water dioxide
Plants use the sugar produced by photosynthesis to manufacture more complex chemicals, or they metabolize it to provide themselves with energy.
Burning plant matter in a fire releases potential energy stored in the chemical bonds of organic chemicals. During burning, the molecules react with oxygen and break apart to produce carbon dioxide, water, and carbon (soot):
plant + O2 burning CO2 + H2O + C (soot)
other gases heat energy
The flames you see in fire consist of glowing gases released and heated by this reaction. People have burned wood to produce energy for centuries. More recently, plant material (biomass) from crops such as corn and sugar cane has been used to produce ethanol, a flammable alcohol.
• Energy from chemical reactions: A number of inorganic chemicals can burn to produce light and energy. The energy results from exothermic (heat-producing) chemical reactions. A dynamite explosion is an extreme example of such energy production. Recently, researchers have been studying electrochemical devices, such as hydrogen fuel cells, that produce electricity directly from chemical reactions.
• Energy from fossil fuels: Oil, gas, and coal come from organisms that lived long ago, and thus store solar energy that reached the Earth long ago. We refer to these substances as “fossil fuels,” to emphasize that they were derived from ancient organisms and have been preserved in rocks for geologic time. Burning fossil fuels produces energy in the same way that burning plant matter does.
• Energy from nuclear fission: Atoms of radioactive elements can split into smaller pieces, a process called nuclear fission. During fission, a tiny amount of mass is transformed into a large amount of energy, called nuclear energy. This type of energy runs nuclear power plants and nuclear submarines.
• Energy from Earth’s internal heat: Some of Earth’s internalenergy dates fromthe birth of the planet,while some is produced by radioactive decay in minerals. This internal energy heats water underground.The resulting hot water, when transformed to steam, provides geothermal energy that can drive turbines.
Task 3. Match the following words and word combination and their definitions:
A. Nuclear fusion
B. Photosynthesis
C. Organic chemicals
D. Soot
E. Exothermic chemical reaction
F. Nuclear fission
G. Turbine
H. Waterwheel
I. Windmill
J. Solar-energy panel
1. The splitting of an atomic nucleus into approximately equal parts, either spontaneously or as a result of the impact of a particle usually with an associated release of energy
2. A process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. It occurs in plants, algae, and many species of bacteria
3. A rotary engine that extracts energy from a fluid flow and converts it into useful work.
4. Machine for tapping the energy of running or falling water by means of a set of paddles or buckets mounted around a wheel. The force of the moving water against the paddles, or the weight of water poured into the buckets, rotates the wheel. The resulting power is transmitted to machinery via the shaft of the wheel.
5. Any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon.
6. The process by which two or more atomic nuclei join together to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy.
7. Machine for harnessing the energy of the wind using sails mounted on a rotating shaft. The sails are mounted at an angle or are given a slight twist, so that the force of wind against them has two components, one of which, in the plane of the sails, causes rotation.
8. A chemical reaction that is accompanied by the release of heat. In other words, the energy needed for the reaction to occur is less than the total energy released. As a result of this, the extra energy is released, usually in the form of heat.
9. Device that converts the energy of sunlight directly into electricity by the photovoltaic effect.
10. Black or dull brown deposit of fine powder resulting from incomplete combustion of fuel of high carbon content, e.g., coal, wood, and oil. It consists chiefly of amorphous carbon and tarry substances that cause it to adhere to surfaces.
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