Answer to Question #89935 in Mechanics | Relativity for Murari

Question

I asked a question that sound of firecracker burst in one direction comes from a different direction you told it's reason as reflection of sound
But if it was reflection of sound then why doesn't that sound echo as reflection of sound causes echoes
The sound from different direction is heard as if it was coming from that direction only

Answer 1

1. The most likely is the result of the propagation of sound with reflection. Reflection from buildings allows you to hear sound from other directions. In this case, the absence of echo is possible if there is a reflecting (scattering) object between the source and receiver of the sound (in case of rectilinear propagation). For example: the sound receiver is located indoors with a window that does not fall into the area of ​​rectilinear sound propagation. If a building is located opposite the window, the sound from the source to the receiver will propagate as a result of reflection from the building opposite the window and create the effect of propagation from another direction.

2. Less likely is the result of the influence of sound refraction or / and the result of the influence of turbulence in the surface layers of the atmosphere. The atmosphere is heterogeneous, so the sound in it does not extend in a straight line, but along a rather bizarre trajectory. Sound refraction in the atmosphere is due to spatial changes in air temperature, wind speed and direction. With height, the temperature usually decreases (to heights of 15–20 km) and the speed of sound decreases, so the rays from a sound source near the earth’s surface bend upwards and the sound, starting from a certain distance, ceases to be audible. If the air temperature increases with height (temperature inversion, often occurring at night), then the rays bend downwards and the sound spreads over long distances. When the sound propagates upwind, the rays bend upward, and when propagating in the wind - to the earth's surface. Sound refraction can lead to the formation of silent zones and abnormal hearing zones. Acoustic silence zone (acoustic shadow zone) is an area in which the sound of remote powerful sources (gunfire, explosion, etc.) is not audible, while at large distances it appears again (anomalous audibility zone). Zones of silence usually have the shape of an irregular ring surrounding the sound source on the earth's surface. The inner radius of the 1st zone of silence is usually 20–80 km, sometimes it reaches 150 km; outer radius can reach 400 km.