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J. Perelman
"Entertaining physics". Book 1.
Chapter 10. Sound and hearing

WHERE CHATTERS GRASSHOPPER?

Very often we mistake not determined by the distance and the direction is sounding subject.

Our ears quite well distinguish, came the sound of the shot to the right or to the left of us.


Centre shot: right or left?

But they are often powerless to determine the position of the sound source, if it is directly in front of or behind us: a shot made ahead, often heard as heard in the back.


Centre shot?

We can in such cases be distinguished only by the power of sound - distant shot from close.

Here is an experience that can teaches us a lot. Put someone in the middle of the room with a blindfold and ask him to sit quietly, without turning his head. Then, picking up two coins, hit them one on another, all the time remaining in the vertical plane that cuts the head of your guest in half between his eyes. Let the person try to guess the location you clicked coins. The result is just incredible: the sound produced in one corner of the room, and the subject indicates exactly the opposite point!

If you depart from the said plane of symmetry of the head to the side, errors will not be so rude. It is clear: now the sound near the ear of your guest heard a little earlier and louder, so that the examinee can determine the origins of the sound.

This experience explains, incidentally, why is it so hard to notice whirring in the grass grasshopper. A sharp sound is heard in two steps from you, to the right of the track. You look, but see nothing; the sound is heard already left. Turn your head there, but the sound already heard from some third place. The sooner you turn in the direction of whirring sound, the quicker are the jumps are invisible musician. Actually, however, the insect is sitting at the same place; his amazing jumping is a figment of your imagination, a result of fraud hearing. Error in your that you turn your head, placing it just so that the grasshopper is in the plane of symmetry of your head. Under this condition, as we know, it is easy to err in the direction of the sound: rattle grasshopper dealt in front of you, but you mistakenly consider it in the opposite direction.

Hence, the practical conclusion: if you want to determine where one can hear the sound of the grasshopper, the singing of the cuckoo and the like distant sounds, do not turn the face toward the sound, but on the contrary, loosen it aside. However, we've been doing, when, as they say, “suspicious”.

Entertaining physics J. Perelman

 




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