Why does breathing helium make our voices sound Mickey Mouse-ish? Is there anything we can drink that will have the same effect for a longer period? – AP
The pitch of your voice is largely determined by the dimensions of your larynx. That’s why men, with their larger larynxes, generally have lower voices than women. While the sound of your voice originates in the vibrations of your vocal cords, string-shaped objects aren’t very good at emitting sound. Just as a violin employs a box to assist its strings in producing sound, you use your larynx to assist your vocal cords in producing sound. Which pitches your larynx produces well depends on its size and on the speed of sound. Both of these factors are important because the air itself vibrates and either decreasing the size of your larynx or allowing sound to move faster from one side of it to the other will raise the pitch of your voice. Because the speed of sound is much higher in helium (965 m/s) than it is in air (331 m/s), the pitch of your voice rises when you breathe in helium gas. However, as soon as the helium has left your lungs and is replaced by air, your voice returns to normal. Apart from breathing gases with high speeds of sound, there isn’t anything else that will work. You can’t live on pure helium gas, so the only way to sustain this effect would be to breath a helium/oxygen mixture instead of air. Some deep-sea divers do just that and their voices continue to sound “Mickey Mouse-ish” as long as they breathe this mixture.