How far behind a plane is its noise?
Nice, but very wrong. This describes the case of a plane suddenly appearing in mid-air and starting to make noise, something, planes rarely do (maybe in the Bermuda triangle). It&#x27;s like thunder after lightning, or seeing a ball fly before hearing it being kicked when you&#x27;re far away.<p>The aircraft, however, is flying <i>for a long time</i>, certainly it was flying and making noise much earlier than when it is passing the observer. As long as it flies subsonically, i.e. sound outpaces the aircraft - which is the case for every single commercial plane - the sound may be able to reach you much much earlier than the plane: As an example, take an aircraft flying with 100 m&#x2F;s directly towards you. With every second flying, the sound will gain another 200 m distance relative to the aircraft (speed of sound ~300 m&#x2F;s).<p>If you&#x27;re 100km away, the aircraft will reach you after 1000s, the sound has reached you after 333s, i.e. <i>ahead</i> of the aircraft. If you&#x27;re 200km away, the aircraft will reach you after 2000s and the sound has reached you after 667s.<p>So, how come it sounds like the sound of the plane is <i>behind</i> the plane? It&#x27;s got to do with sound attenuation in the atmosphere and your hearing threshold.<p>So, it&#x27;s not at all like in the article.<p>Somewhat minor nitpicks:<p>- The aircraft is drawn to essentially fly with Mach 1, i.e. at the speed of sound, as the position of the plane relative to the wave does not linearly increase with time. Essentially all airplanes you see are flying subsonically (unless you&#x27;re in the military).<p>- &quot;If the plane was moving very slowly, it wouldn’t outpace its sound by much.&quot; That&#x27;s completely wrong. &quot;very slow&quot; aircraft are much slower than their sound, and all commercial aircraft still are slower than their sound, all of them are outpaced by their sound rather than the other way around.<p>[Edit: typos &amp; math]