National Geographic Photo of the Day

Saturday, March 7, 2009

A Vocal Variety...... Helium and Anti-helium...

Check out this funny video (an excerpt from a Mythbusters episode).

The radical change in his voice, as he says, is because of the Helium he inhales at first. Helium is six times lighter than air. When a series of compression waves (your voice) leave the helium in your lungs and hit the denser air, the wave train is suddenly slowed down. The wave in front is slowed first while the wave behind it is still moving fast. Then the second wave is slowed while the third is still moving fast, and so on. It's like fast moving traffic on an open freeway suddenly coming to a slow point in the road, all the cars bunch up close to each other.

Your ear interprets closely bunched sound waves as a higher pitch than widely spaced waves. So when your voice originates in helium and then travels through the air to someone's ear, it
sounds higher. If both you and the listener were in a room filled with helium, your voice would get to their ears faster than normal, but there would be no pitch change.

The reverse is true in the case of his voice deepening when he inhales Sulphur Hexafluoride. Sulfur hexafluoride (abbreviated SF6 and also called Anti-Helium because its six times heavier than air) is not poisonous and can affect the sound of a person's voice if it is inhaled in small quantities (again, don't try this at home). When SF6 is inhaled, the pitch of a person's voice decreases dramatically because the speed of sound in SF6 is considerably less than it is in air.

Do not fill your lungs with any of these gases - it can lead to hypoxia and fainting. As a disclaimer, I am in no way responsible for any stupid stuff you try, or if you inhale some crap and die ;-) So, please stay safe.


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