physics question #7766



Edward, a 14 year old male from the Internet asks on April 28, 2001,

Q:

When two open metal tubes on the roof of the car for the purpose of use as a roof rack, are travelling or reaching a certain speed, let's say over 60 km/h, a loud whistling noise is heard from the rack. Why does this happen? How can we solve this problem? Why do females tend to sing higher notes than males?

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the answer

Barry Shell answered on April 29, 2001, A:

This probably happens because the column of air in the rack is vibrating at a resonant frequency. The vibration is a function of the energy applied to the open end of the tube, its length and probably other things. As you go faster, the air hits the end faster and when it gets to the right speed, the sound begins. I don't know for sure, but possibly putting a piece of duct tape or something over the end, or plugging it with a piece of plastic or a cork might work. You can try filling the tube with something like paper or plastic, too, if the first idea doesn't work. The shorter or smaller the vibrating thing, the higher the frequency or pitch. Since women are on average smaller than men, and on average have smaller vocal cords, their voices, on average, sound higher because the smaller vocal cords vibrate at a higher frequency.

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