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#111
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Quote:
Last edited by Fraser; 05-03-2010 at 03:33 AM. |
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#112
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I added info to my previous post .
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#113
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Quote:
(You have to use seconds, grams, and meters for everything in that formula. Never cm or kg.) Crunching the "height required" for Vt is not straightforward. The approach to terminal velocity is asymptotic due to all these pesky aerodrag forces, which increase in a non-linear fashion. I was mistaken earller: it's not the vacuum-driven constant 9.8m/sec^2 that was drillied into us in high school and college. So the 9.8 acceleration decreases asymptotically on the approach to Vt. What I think led me astray: the first 2 seconds or so of free-fall (for a truly solid body, not a porous feather) is probably still governed by the 9.8...until the object reaches a sufficiently high velocity (say 25-30 mph) for drag and mass to become factors. Since the physics experiment in college with the heavy and light marbles never attained that speed, my observation of those results (i.e. the marbles reaching the floor simultaneously) led me on the wrong path. For a modest fall of say 150 feet or so, I would guess a steel marble weighing a dozen grams or so would fall at the same rate and cover the same distance as the 2.4-ton X5M. After that, all bets are off. |
#114
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I showed it in post #88, and rounded it to 420 mph, nose first.
I knew that calculating the height was more of a chore, due to the drag forces, which is why I left it for the next poster. This is all fine and well, using the various terminal velocity formulae, but until you get significant drag or approach the terminal velocity, you can effectively ignore the aero effects and treat it as a simple free fall. It depends entirely on the height of the hypothetical cliff, and you have to go to extremes in cliff height before the aero drag matters. Now, if someone had started this with an example of an X5M being dropped out of an airplane, we would need all this complication.
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2007 X3 3.0si, 6 MT, Premium, White Retired: 2008 535i, 6 MT, M Sport, Premium, Space Grey 2003 X5 3.0 Steptronic, Premium, Titanium Silver 2002 325xi 5 MT, Steel Grey 2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue |
#115
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No matter how short the fall, the heavier X5 (assuming everything else is equal) will hit the bottom first.
Last edited by Fraser; 05-04-2010 at 04:44 AM. |
#116
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What the hell is going on with this thread, let's close it!
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---2008 X5 With All Factory Options ---2002 Black S 500 Designo Edition |
#117
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yeh this thread got jacked by bunch of geeks big time.
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#118
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you need to smash your pedal to the floor a few times
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2001 X5 4.4i WHITE-Loaded like a baby's diaper SOLD |
#119
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Hey, it's all entertainment. With 2500 views now, this is the 7th most popular thread ever on the X///M forum (not counting the stickies).
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2007 X3 3.0si, 6 MT, Premium, White Retired: 2008 535i, 6 MT, M Sport, Premium, Space Grey 2003 X5 3.0 Steptronic, Premium, Titanium Silver 2002 325xi 5 MT, Steel Grey 2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue |
#120
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You know, when I was a teenager I'd probably take offense at that label, but nowadays I take "geek" as a compliment! Thanks bro!
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