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#101
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Nothing in my original post is false. Perhaps you need to re-read it. |
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#102
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StanF18: Provided the cliff is high enough for the two objects in question to reach their respective terminal velocities, the heavier object would reach the ground first provided the aero factors were the same. You original post says that weight/mass is not a factor, it is.
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#103
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The best way to illustrate the failure and misleading nature of your example is as follows. Take a solid iron cannonball (Cannonball A). Weigh it. Let's say it weighs 1000 pounds. Now: Take anther solid iron cannonball (Cannonball B) of the same shape and weight. if there was a way to then open up Cannonball B into 2 halves (like an orange), and take out let's say a good 500 pound chunk of iron from its center...then close it up and re-weld it to its original shape....You now have iron cannonball A weighing 1000 pounds. Yes? And you have iron cannonball B of the same size and material, but you have cored out its center and it NOW weighs only 500 pounds. How much $$$ do you want to bet that if you drop these 2 off a cliff at the same time, they would hit the bottom at the same time? That's because the drag acting on both is the same, due to the EXTERIOR PORTION of the cannonballs being the same size and material. The porosity and cross-sectional area is equivalent. At this point mass does NOT enter the equation. Similarly, your example is misleading when applied to the 2 free-falling vehicles. Unlike the multiple exposed surfaces of the bird feather vs. the lead feather, The 3 fat guys inside the 4.6is have ZERO effect on the drag vector. So while their vehicle is consequently heavier, it would still accelerate at the same rate as the lighter X5M. And EVEN if the cliff is ultra high, and both vehicles eventually stop accelerating and start falling at a steady speed...i.e. TERMINAL VELOCITY....they would STILL hit bottom at the same time. Because the acceleration of gravity is a constant for ALL objects. And the drag that counteracts this "g" vector is equivalent for the 2 vehicles, regardless of the extra mass inside the 4.6is. Last edited by StanF18; 05-02-2010 at 08:11 PM. |
#104
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__________________
Current Garage: 2015 Singapore Grey M6 Gran Coupe (ED - May 2014) -new car 2008 Imola Red E60 M5 - love of my life 2012 Alpine White LCI E70 X5 50i w/ LCI Aero Kit and Rocker Panels - wife and kids car Retired: 2009 Jet Black E70 X5 4.8i Sport w/ Aero Kit 2007 Jet Black E60 530xi M Sport 2003 Jet Black E39 530i Sport |
#105
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#106
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The feather is still a bad example...while the masses of the 2 feathers are different, the differences in Cd and A (cross-sectional area) are the main "culprits" in the much lower terminal velocity of the bird feather vs. the lead feather. |
#107
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time to call in Mythbusters methinks .
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#108
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I'm sure that Wikipedia is right on this occasion. Easier to post that link that upload page images of the physics book that I still have from old university days which has the same basic explanation of terminal velocity of a free-falling object. It gives the variables as mass, aero drag (Cd x cross-section area) and the density of the medium through which the object is falling. It also notes that while acceleration due to gravity is always the same in a perfect vacuum there is some variation in acceleration in a medium like air that is dependent on the density of the object vs the density of the medium, with denser objects accelerating faster than less dense objects in the same medium. In this case our X5 stuffed with bodies will be denser than an empty X5 so not only will the heavier X5 (+ bodies) achieve a higher terminal velocity, it will also accelerate slightly faster in getting to its terminal velocity.
Agreed that the feather example is not good as it would be impossible to replicate the feather's Cd in a lead casting. |
#109
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paging NASA , maybe an astrophysics dude could answer .
maybe electro magnetic forces and the composition of materials used in the experiments affect the results of said experiments . anyhoo , I was given a figure to determine my terminal velocity in stable freefall and everyone has a predetermined figure . when doing relative freefall ( formation ) some dudes required to wear oversleeves to create drag and some dudes required to wear weights to balance their body . everyone had to adjust body position to faal at the same speed , weight and drag being a factor to terminal velocity . thrillseekers would pay for a tandem jump whereby they would be attached to a skydiver to experience high altitude freefall . the tandem skydivers would fall faster than a single skydiver due to the weight factor with little additional drag so a small drogue parachute was deployed after exiting the aircraft to attain 120mph , it also improved stability . A solo parachute was around 200 sq/ft A tandem parachute was around 400sq/ft so why do you think a tandem required double the canopy area . climbing to 12000 ft in a cessna 206 took a boringly long time and sometimes the weather or windspeed changed , so we were told to return to the drop zone, the pilot would point straight at the ground and very soon reached a speed where we would become weightless . need I say more . edit : re the cessna , we were effectively weightless as soon as it began to descend . as it got faster we would begin to float around to a point where we had to hold on to the aircraft and when we held on I`m sure we were creating some sort if drag on the aircraft . whether this has anything to do with the fact we consist of mainly water I don`t know . Last edited by amacman; 05-03-2010 at 10:33 AM. |
#110
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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 |
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