|MadSci Network: Physics|
Sound travels just as far during the night as it does during the day, since the only one thing that can affect sound transmission is the composition of the medium... In this case, the medium is air, and the composition of air does not change between night and day in any way that would signifficantly change the way sound travels... However, you have made an observation about how sound travels at night, and indeed, you can hear distant sounds more clearly during the night than during the day... But why is that? The human ear becomes less sensitive to weak sounds in the prescence of louder sounds. This phenomenon is called masking. During the day, the ambient noise level tends to be higher, because there are cars driving on the streets, people walking by, doors opening and closing, birds flapping their wings and singing, and so on. The prescense of all this sounds during the day makes it hard to hear faint distant sounds, not because their waves cannot travel as far, the waves travel just as far, but our sensitivity to those sounds is impaired by the masking phenomenon. We could say that the ambient noise "masks" your friend shouting in the distance. During the night, everyone is asleep, very few, almost no cars at all can be seen driving by, most birds are asleep too, and it is generally more quiet. Since it is so quiet, its also easy to hear a faint distant sound very easily. This difference between night and day can also seem to make echoes louder. And again, echoes are not louder at night than during the day, but, since echoes are distant and faint, just like any distant faint sound, they are also masked away by louder ambient noise. This important example shows us how an observation such as yours can be very true: You can in fact hear distant sounds more clearly at night, but the mechanism responsible for this observation can be very different from what we expect. Your mad scientist, Aurelio R. Ramos
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