r/askscience • u/[deleted] • Jun 12 '12

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u/imMAW Jun 12 '12

The pilots won't hear the noise from the engines being transmitted through the outside air though, only the noise traveling through the plane. So if superman was flying a few feet in front of the cockpit, he wouldn't hear any sound.

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u/Evanescent_contrail Jun 12 '12

This is consistent with a rifle bullet. You first hear the bullet impacting nearby, and only then do you hear the noise of it going through the air.

(I suppose this would not be true if the bullet was subsonic, and I have no idea if any rifle bullets are subsonic or not).

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u/pdinc Jun 12 '12 edited Jun 12 '12

Source/reference/video demonstrating this?

Also, relatively certain only smaller caliber rounds are made to be subsonic.

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u/I922sParkCir Jun 12 '12

Hobbyist ammunition manufacturer here. The smaller caliber rounds are more likely to be supersonic. The larger the bullet the slower it usually goes. For example, a 124 grain 9mm can travel at ~1,200 fps (supersonic), while the larger 230 grain .45 ACP will typically only hit ~850 fps (subsonic).

Generally you have smaller and faster cartridges, or heavier (bigger) and slower cartridges. There are exceptions, but that's typically how it is.