今天前程百利小编为大家分享的是托福听力背景知识之ENERGY。这些背景知识是需要日积月累的，大家快存下来，为托福听力备考做准备。
An early source of energy, or prime mover, used by humans was animal power, i.e., the energy obtained from domesticated animals. Later, as civilization developed, wind power was harnessed to drive ships and turn windmills, and streams and rivers were diverted to turn water wheels (see water power). The rotating shaft of a windmill or water wheel could then be used to crush grain, to raise water from a well, or to serve any number of other uses. The motion of the wind and water, as well as the motion of the wheel or shaft, represents a form of mechanical energy.
…NEW ENERGY source is tidal energy. Experimental systems have been set up to harness the energy released in the twice-daily ebb and flow of the ocean’s tides
LAVA
Lava is magma that breaks the surface and erupts from a volcano. If the magma is very fluid, it flows rapidly down the volcano’s slopes. Lava that is more sticky and less fluid moves slower. Lava flows that have a continuous, smooth, ropy, or billowy surface are called pahoehoe (pronounced pah HOH ee hoh ee) flows; while a a (pronounced ah ah) flows have a jagged surface composed of loose, irregularly shaped lava chunks. Once cooled, pahoehoe forms smooth rocks, while a a forms jagged rocks.
ALLOY
Alloys are used more extensively than pure metals because they can be engineered to have specific properties. For example, they may be poorer conductors of heat and electricity, harder, or more resistant to corrosion. Alloys of iron and carbon include cast iron and steels; brass and bronze are important alloys of copper; amalgams are alloys that contain mercury; and chromium is an important additive in stainless steel. Because pure gold and silver are soft, they are often alloyed with one another or with other metals. New alloys are being engineered for use in new technology, including materials for the space program. Metallic glasses and crystalline alloys have also been developed, and metal alloys are sometimes bonded with ceramics, graphites, and organic materials as composites.
好了，以上就是前程百利小编为大家整理托福听力背景知识之ENERGY。希望能在备考的路上助大家一臂之力。最后，小编祝大家在托福考试中取得好成绩!
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