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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.|Imagine having to do the work of a jackhammer using a sledgehammer or a pickaxe, and you'll quickly understand how important this one machine is to the construction industry. Concrete, asphalt and rock are hard -- sometimes really hard -- to work with. Thanks to that toughness, roads and building foundations last for decades. But when rebuilding or mining projects require removing these unyielding substances, a sledgehammer just isn't enough. That's when jackhammers come in handy. T-shaped jackhammers are among the most iconic, fearsome and ear-shattering tools on construction and demolition sites. Because they combine two fundamental human hand tools (a hammer and a chisel) in one mechanized body, they are also one of the most useful. We could always go back to the old way -- using heavy-headed sledgehammers -- but there probably aren't enough chiropractors in the world to keep construction workers' backs aligned. Plus, sledgehammers are achingly slow.




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