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Natural Science Forum / Physics / Acoustics / February 2004Layman has a Sonic Boom question
All, Hi. I'm just a non-physics type who has a question. It isn't an important question, it is kind of frivolous. It involves sonic booms. The question is also pretty dorky. What effects do sonic booms have on people? How rough is the force? I'm talking along the lines of a jet jamming through a city somewhere at street level. What effects would it have on people at very close range? Tissue damage? Nose bleeds? Burst eardrums? Or mostly just fright? What about effects on Cars? Glass? Also, how would mass affect it? What about a human-sized object causing a sonic boom. Yes, this is basically a comic-book question. I'm wondering what the real effects would be of some vehicle blasting through a populated city area at near street level? And what would the result be if the object were human-sized, like the Flash (DC Comics) for example? Thanks for any patience in dealing with this question. Lewis >What effects do sonic booms have on people? How rough is the force? >I'm talking along the lines of a jet jamming through a city somewhere >at street level. What effects would it have on people at very close >range? Tissue damage? Nose bleeds? Burst eardrums? Or mostly just >fright? What about effects on Cars? Glass? Just annoyance and startle. The biggest sonic boom ever recorded was 144 psf, from an F-4 flying at 100 feet above the ground. There were people under the flight track. (Part of the experiment.) No harm, but after the first couple they reported a feeling of dread when the next one was approaching. It is unlikely that a sonic boom can be much louder than that, because it's not going to exceed the surface pressure on the aircraft. For reference, the initial level of any physical damage is eardrums blowing out at around 800 psf. There would be hearing damage at levels lower than eardrum damage, but I'm not quite sure at what level. Glass breaks at pressures of a couple of psf and higher. Not a high percentage at that level, but when you get over 10 to 20 psf you should expect a lot of windows to break. >Also, how would mass affect it? What about a human-sized object >causing a sonic boom. Mass doesn't affect it. Weight does for a lifting body, but at low altitudes boom is dominated by the volume. >Yes, this is basically a comic-book question. I'm wondering what the >real effects would be of some vehicle blasting through a populated >city area at near street level? And what would the result be if the >object were human-sized, like the Flash (DC Comics) for example? I doubt if Flash would make a sonic boom. There is something about the way that he moves - don't his molecules thin out or something? Superman is a different matter - man of steel, very solid. But he holds his arms out in front when he flies, and that would give him a smoother aerodynamic shape. Wouldn't surprise me if he worked it so he generated a near-field shaped signature of the kind that delays (or prevents) formation of actual shock waves. He does make that sort of whisling sound, but that's comforting rather than startling - unless you're a criminal. >Thanks for any patience in dealing with this question. Good question. Ken, >I doubt if Flash would make a sonic boom. There is something about >the way that he moves - don't his molecules thin out or something? [quoted text clipped - 4 lines] >he generated a near-field shaped signature of the kind that delays (or >prevents) formation of actual shock waves. Thanks for the quick reply. Much appreciated! And thanks to anyone else who chimes in. An non-player character of my own devising in our local Champions (super hero roleplaying) game can break the sound barrier, and the character is fairly solid. Anyway, it sounds like it would be possibly realistic to have a sonic boom and have it be a little startling, but nothing too severe. I like it ... nice and cinematic. Thanks Again! Lewis >>What effects do sonic booms have on people? How rough is the force? >>I'm talking along the lines of a jet jamming through a city somewhere [quoted text clipped - 8 lines] >track. (Part of the experiment.) No harm, but after the first couple >they reported a feeling of dread when the next one was approaching. I know there are limitations on max speed at low altitude. Something about the aircraft breaking up! I'm pretty sure an F-15 would do something at max speed! greg |
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