Is it true that sound travels further at night and why?
362504
Sound is a waveform passing through a medium (in this case air). Cooler night air is denser than warm daytime air and therefore easier to travel through and propagate. Other factors already mentioned contribute to it seeming louder, but do not help it to travel further.
1106633
Simple observation demonstrates that when you roll down a window or open a  door, the sound outside will get louder.\n\nThis is because you windows act as a sound 'insulator' which both reflects and absorbs the sound energy inside the car. Sound energy won't 'build up' in a car or enclosed space (as opposed to a pot of water on the that 'stores up heat' and continues to get hotter and hotter until it boils). The music won't get louder and louder until you open a window to let it out. \n\nSound really is a wave, and it in itself is not a pure form of energy, but a reaction to a 'energy source' (your speaker). the waves will immediately be absorbed / reflected into surrounding matter - but it's so minimal that you won't notice any real increase of energy or heat inside the car, although it has been said that a person could cook an egg if they left it in front of a speaker at a rock concert, demostrating that there is energy available in sound.\n\nAlso, the same as heat - one open window will cause some heat escape, while more than one will cause a greater heat escape - more sound will escape with multiple windows.\n\n*UPDATE*\n\nTwo windows open would allow more "flow" of sound waves, and in essence, would be louder at the intented target. If you were to just be targeting the "right" side of the car, you would better direct the sound by leaving your left windows closed and your right windows open, because some of the sound waves could reflect off your left windows like a mirror. The difference, however, would be minimal.
923187
Since sound travels faster than the speed of the train,there will be overlapping of sound as it approaches you (i.e Doppler effect) the pitch is high and highest when it crosses you..The closer you are to the track ,more will be the effect.As the train passes away from you the sound dies down in a drawn out fashion.
706798
The sound energy is being dissipated uniformly in all directions.\nThe intensity of the sound energy decreases inversely to\nthe distance squared.\n\nSo from a location 78m versus 22m, the decrease in intensity\nis a factor of (22/78)^2.  And teh actual intenisty is then\n\n3x10^-4 x (22/78)^2.
790288
This is due to the Doppler effect. You know how when a car is coming towards you it has a higher pitch sound, and when it is driving away from you it has a lower pitch sound? This is called the Doppler effect, and it basically works like this:\nSound (and light) are waves that are emitted by the source (in this case the car, and as the source travels towards or away from you, these waves bunch up (towards) or spread out (away). This bunching / spreading causes the waves to interact with eachother. Basically, if the source is moving away the wave's frequency decreases (so the sound is lower) and as the source moves towards you, the frequency increases (so the sound is higher). It works the same with light (red for lower frequencies, blue for higher frequencies).\nSo, does this mean that all the stars out there are moving? Hell yeah! And they're moving pretty fast, too! The vast majority are moving away (so most are red-shifted), bt a few are racing towards us, so they are blue-shifted. The light from the big bang that created the universe itself is moving away from us so quickly, it has shifted past red and all the way to the microwave spectrum (yup, that stuff you use to reheat your morning coffee), and appears as background radiation.\nHope this helps.
516568
when you travel faster than the speed of sound.
629963
Besides the obvious "that's just how the universe and nature is" reason, it might be because sound is the propogation of mechanical waves.  It needs things like air to travel through and disturb the molecules.  Light is just itself (in some wavelength form) and travels that quickly.
300017
they come out at night, mostly
18204
My vote would have to go to the lack of "sound pollution", the brother of "light pollution".\n\nFor instance, after midnight, most people are tucked into bed and, therefore, no one is awake to make noise. So in essence, those floor boards creak all the time while the house is settling, but you only hear it when there is no other "extra" noise.\n\nOr you could have ghosts! Hope this helps! :O
848319
this may be a simpler answer.As a train moves away from you the sound frequency changes.Similarly an observer on Earth(powerful telescopes)are receiving light from galaxies at changing frequencies.So we assume that they are moving away from us.Since every thing is moving away from us, the universe is expanding from the point of view of an observer on earth.
148
In a sense, any microphone is picking up sounds from the past, due to the speed of sound. This is similar to what you mentioned with radio telescopes.\n\nThe main differences are 1) velocity -- light moves at about 1 foot per nanosecond while sound moves around 1 foot per 1/1000 second, and 2) that sound moving though a medium diffuses quite rapidly. Something really loud, like thunder, you might hear from 20-30 seconds away. For normal, everyday sounds, the delay won't be more than maybe a few tenths of a second.
512696
My guess is you are talking about being able to see the flashing lights of a plane at night but cant hear it. Or seeing a high plane with contrails during the day but cant hear that either. Light travels 186,282 mps while sound is only 1100 feet per second. So you see something your mind knows is making noise, but cant hear it because of the distance. Now if the sound has not dispersed through the air by the time it gets to you, then you hear it, but since you cant see what is making it, you dont realize it.
580593
If a lightning strike is a sufficient distance from the observer, sound from the strike will not be heard. These silent bolts are called heat lightning. Lightning bolts produce thunder, but the thunder sound does not travel all the way to the observer if the observer is too far away.\n\nThe movement of sound in the atmosphere depends on the atmospheric properties of the air such as temperature and density. Because temperature and density change with height, the sound of thunder is refracted through the troposphere. This refraction results in spaces of volume in which the thunder does not propagate through.\n\nBolt Lightning is your average everyday cloud to ground lightning caused by a differnce in charge between the cloud and the ground. Lightning is caused by static electrical charges, just like the kind you get from rubbing your sock feet across a carpeted floor (just much much much larger and more powerful).
726542
Only if the sound can prevent Oxygen to the fire source.\n\nHowever, If the sound could cause turbulence in the air surrounding fire....Possible.\n\nMav.
1005278
Yes, light travels faster than sound. You can tell from several \nexamples. The best would probably be that of lightning and thunder. The next \ntime during a storm, if you notice when lightning flashes across the sky and \nwhen you hear thunder, you will find that it is always the lightning that \nflashes before the thunder. This is because lightning (i.e. light) travels \nfaster than thunder (i.e. sound), and reaches you faster, so that you see the \nlightning before you hear the thunder. In fact, light is enormously faster than \nsound. Light travels at 300,000,000 metres per second (i.e. 300 million metres \nper second), while poor old sound travels only at 330 metres per second.
798869
You cannot hear a plane when it is flying at 30,000 feet - it would be like hearing a bus driving in a city 5 miles away. So the only time you hear planes is when they are lower, approaching airports.\n\nAll airports operate nightime curfews to keep air traffic noise down. Long haul flights have to be timed to take account of these, even if they overfly some areas at their cruising altitude in the middle of the night.
274177
The volume change is only a matter of distance from the horn to you.\n\n As a sound emitter approaches you, the frequency change, doppler effect, is caused by the shortening of the wave length as the back end of the wave is "compressed" against the front of the wave . Shortened wave length equates to higher frequency for approaching sounders. \n\nAs an emitter moves away from you, the back end of the wave is stretched out away from the front end of the wave, the wave length increases, and the frequency decreases.