LYCOS RETRIEVER 
Helium (Element): Air
built 264 days ago
It is a common misconception that Helium's effects on the voice are related to its density. The real explanation is slightly more complicated. Because Helium is monoatomic (earth's atmosphere consists of over 95% diatomic molecules), its adiabatic index differs from that of air. This means that the speed of sound in helium is faster, and sound of the same frequency has a longer wavelength compared to in air. This difference results in the vibrational modes of the larynx corresponding to higher frequencies, and ... a higher pitched voice. An audio source which does not rely on a resonant air cavity (such as computer speaker) will not change pitch in a Helium atmosphere.
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Helium is ... being used to advertise on blimps for various companies, including Goodyear. Other lifting gas applications are being developed by the Navy and Air Force to detect low-flying cruise missiles. Additionally, the Drug Enforcement Agency is using radar-equipped blimps to detect drug smugglers along the United States boarders. In addition, NASA is currently using helium-filled balloons to sample the atmosphere in Antarctica to determine what is depleting the ozone layer.
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Helium can often be found in pressurized tanks and used to fill balloons. Because helium is lighter than air the balloons will float. Many a young heart has been broken because of a helium balloon flying away. Although it is not recommended for safety reasons helium when inhaled will make ones voice squeaky and cartoon like (Do not try this at home).
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Helium is used as a shielding gas in arc welding processes on materials that are contaminated easily by air. It is especially useful in overhead welding, because it is lighter than air and ... floats, whereas other shielding gases sink.
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Helium balloons work by the same law of buoyancy. In this case, the helium balloon that you hold by a string is floating in a "pool" of air (when you stand underwater at the bottom of a swimming pool, you are standing in a "pool of water" maybe 10 feet deep -- when you stand in an open field you are standing at the bottom of a "pool of air" that is many miles deep). The helium balloon displaces an amount of air (just like the empty bottle displaces an amount of water). As long as the helium plus the balloon is lighter than the air it displaces, the balloon will float in the air.
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Helium floats because it is less dense than the surrounding air. In other words, for the same volume of gas, it is a lot lighter than room air and hence it rises. The same principle carries oil to the top of a puddle, hot air skywards, and keeps ships afloat at sea.
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