by 3 hours ago
ANSWERS: 5
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Helium is less dense than the air we normally breathe (Air is made up of approx 80% nitrogen and 20% oxygen) Updated longer answer: When we talk air passes out from our lungs through our vocal chords and is caused to vibrate and you hear the words. When you mix helium with air the resulting mix is less dense so as you breathe out the timbre of your voice is altered. The spped of sound in a less dense helium/air mix is higher than in just air. You are increasing the speed of sound of your voice when breathing out this less dense mixture and this increase in speed will affect the frequencies that make up your 'voice'. If the frequencies are affected the timbre is affected too. A more dense gas may have a very wierd affect. Strictly speaking although most people say it is the pitch that changes, it is the actually the 'timbre' which is changed, as your vocal chords produce the same shapes and therefore the same pitch.
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This is all because of the speed of sound. The speed of sound is different in He gas than in N80/O20 gas (normal atmosphere). From: http://en.wikipedia.org/wiki/Balloon: Partygoers sometimes entertain each other by untying a balloon and inhaling the helium. Because the speed of sound in helium is about twice that in air, the helium causes the vocal tract to become more responsive to high-pitched sounds and less responsive to lower ones. The result is a voice that sounds high-pitched (and usually very funny).
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It's a little complex, but here goes: 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 thus 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. If you took an orchestra to Jupiter (whose atmosphere is primarily Helium and Hydrogen), the winds would be out of tune but the strings would remain unchanged.
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The speed of sound depends on the denisity and pressure of the gas it travels through. The greater the pressure, the greater the speed. The greater the density, the smaller the speed. Helium is less dense than air. So as long as the pressure is about the same or greater, the speed of sound will increase. If the sound waves have a higher speed, they will have a higher frequency, and as such, a higher pitch.
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Helium has a much lower density (specific gravity) than air. This affects the resonant frequencies of the vocal tract, i.e., the fundamental pitch and mix of harmonics at which the vocal cords vibrate, giving rise to the "chipmunk" voice. The gas viscosity may be a factor, too. Just as breathing helium raises the pitch and changes the quality of the voice, an opposite effect is seen when breathing nitrous oxide, which has a higher density than air. N2O lowers/deepens the pitch/quality of the voice. I don't think the speed of sound in the gas is of importance in producing this effect. The usual caution about breathing helium from balloons: Don't forget to take breaths of air in between. 100% helium = 0% oxygen (air has 21%). As for N2O: Don't even THINK about it!
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