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


When passengers Jules-vernova projectile flew to the moon, they were puzzled by the fact that he had not heard the sound of a shot colossal cannons erupted from his mouth. Otherwise it could not be. How would deafening was the noise, the speed of propagation of him (as it does all sound in air) was equal to only 340 m/s, the projectile was moving with a speed of 11 000 m/s. It is clear that the sound of the shot could not reach the ears of the passengers: the projectile ahead of the sound.

But as is the case with these shells and bullets: are they faster than sound or the sound surpasses them and warns the victim of approaching deadly projectile?

Modern rifles inform the bullets when shot speed, almost three times greater than the speed of sound in air, it was about 900 meters per second (the speed of sound at 0° is equal to 332 m/sec). However, the sound is distributed evenly, the bullet flies, slowing the speed of its flight. However, for the most part, the way the bullet is still moving faster than sound. From here directly follows that if in a firefight, you hear the sound of the shot or the whistling of bullets, you can not worry: this bullet you already passed. Bullet surpass the sound of the shot, and if the bullet will strike his victim, the latter will be killed before the sound of the shot, which sent the bullet to reach her ear.

Entertaining physics J. Perelman


System Orphus


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