I live near some flight paths so a lingering sound is normal but recently somewhere else a military style jet flew over head and the sound lasted much longer at a very high volume, long after we could see it anymore – why?
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Sound travels pretty slow relative to light
Sound moves at just 343 m/s, but planes tend to cruise up at 10,000+ meters while moving at 800 km/h.
If a plane is up at 10,300 meters(~34k feet) it’ll take 30 seconds for the sound to reach you all the way at ground level. In that time the plane has travelled 6.7 km so you can probably still see it. If that same plane was flying at just 3400 meters then it would take 10 seconds for you to hear the sound and the plane would have traveled 2km but it would have passed across your field of view significantly quicker.
Fighter jets can also make the sound go on long after they’ve passed because they’re engines are just big and noisy and project that noise behind them so you’re not even really hearing noise generated by the plane but instead by a giant speaker built into its tail. The sound from its passing may have been over fairly soon but now you’re in the noise cone of its engine so you can still hear it.
Commercial jets have noise restrictions on how loud their engines can be, military planes do not have to follow those restrictions
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