World, Americas, Special Report

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Third, sound is a vibration that travels through a medium, like a gas, a liquid or a solid object. A sound's source is an object that moves or changes shape very rapidly. For example, if you strike a bell, the bell vibrates in the air. As one side of the bell moves out, it pushes the air molecules next to it, increasing the pressure in that region of the air. This area of higher pressure is a compression. As the side of the bell moves back in, it pulls the molecules apart, creating a lower-pressure region called a rarefaction. The bell then repeats the process, creating a repeating series of compressions and rarefactions. Each repetition is one wavelength of the sound wave. The sound wave travels as the moving molecules push. Pull the molecules around them. Each molecule moves the one next to it in turn. Without this movement of molecules, the sound could not travel, which is why there is no sound in a vacuum.




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