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| Re: Major Amtrak derailment in Philly (1351738) | |||
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Re: Major Amtrak derailment in Philly |
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Posted by AlM on Wed May 13 08:34:46 2015, in response to Re: Major Amtrak derailment in Philly, posted by SelkirkTMO on Wed May 13 01:20:59 2015. Again understanding that we don't know anything yet, let me just say in general that it really takes a lot of excess speed to derail if the track and wheels of the train are in proper condition.That is plain physics. A 1000 foot radius curve might be signed for 30 mph. Sideways force is mv^2/r. So at 30 mph, or 44 ft/sec, v^2/r is 2 ft/sec^2. Since g = 32 ft/sec^2, that means at maximum allowable speed, and with no banking of the curve, the sideways force is only 1/16 g. At 60 mph, everything quadruples, so the sideways force is 1/4 g. I would think that trains aren't so top-heavy that a sideways force of 1/4 could topple one, but now we're getting into engineering rather than physics and my knowledge is pretty much nil. At close to 80 mph, we have nearly doubled the sideways force again, and so we're close to 1/2 g. We know from Spuyten Duyvil that that's too much. IIRC that curve has a radius of about 1000 feet. |
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