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J. Perelman
"Entertaining physics". Book 2.
Chapter 10. Sound. Wave motion

SILENT SOUNDS

There are people who do not hear such harsh sound, as the singing of a cricket or the squeak of a bat. These people are not deaf, their hearing organs in health, and yet they don't hear very high frequencies. Tyndale - the famous English physicist, argued that some people don't even hear the songs of the Sparrow!

In General, our ear perceives not all fluctuations occurring near us. If the body does per second less than 16 fluctuations, we do not hear sound. If it makes more than 15 22 thousand fluctuations, we do not hear it. The upper limit of perception of tones in different persons; in older people, it falls to 6 thousand vibrations per second. That is why there is a strange phenomenon that shrill high tone clearly audible by one person to another but there is.

Many insects (e.g., Komar, cricket) make sounds, the tone of which is 20 thousand vibrations per second; for some ears these colors exist, but not for others. Such insensitive to high tones people enjoy complete silence where others hear a chaos shrill sounds. Tyndale says that he had seen one similar case while Hiking in Switzerland with his friend:

"The meadows on both sides of the road was infested with insects, which to my ears filled the air with its sharp buzzing, but my friend didn't hear: music insects lay outside the boundaries of his ears."

The squeak of a bat a whole octave below the shrill singing of insects, i.e., fluctuations in the air twice less frequent. But there are people for whom the border of perception tones lies below, and bats for them being dumb.

On the contrary, dogs, as determined in the laboratory of academician Pavlov, perceive tones with the number of oscillations to 38 thousand per second.

Entertaining physics J. Perelman

 




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