Home Forums Articles How To's FAQ Register
Go Back   Xoutpost.com > BMW SAV Forums > X ///M Forum
Fluid Motor Union
User Name
Password
Member List Premier Membership Search Today's Posts Mark Forums Read

Xoutpost server transfer and maintenance is occurring....
Xoutpost is currently undergoing a planned server migration.... stay tuned for new developments.... sincerely, the management


Reply
 
LinkBack Thread Tools Display Modes
  #111  
Old 05-03-2010, 02:10 AM
Fraser's Avatar
Member
 
Join Date: Jun 2008
Location: NSW, Australia
Posts: 1,135
Fraser is on a distinguished road
Quote:
Originally Posted by JCL View Post
I'm waiting to see the calculation of how high that cliff has to be for the terminal velocity to be a factor. I did the terminal velocity calculation, above, so I'll let someone else crunch the height calculation. I'm guessing it is up there with the highest cliff on earth, let alone the highest one that has a road to it.
I have no idea how high our cliff has to be for our falling X5s to achieve their terminal velocity. However, the heavier X5 in question (the one with all the big guys in it) will also accelerate faster in freefall than the lighter, empty X5, (given the same aero drag), so even if the cliff is short, the heavier one will still get to the bottom first. The acceleration due to gravity is only constant for all bodies in a perfect vacuum. In a medium such as air, the density of the falling object relative to the density of the medium it is falling through has an effect on acceleration, as slight as it may be. Given that our X5 filled with bodies is denser than the empty X5 it's ahead in this race regardless.

Last edited by Fraser; 05-03-2010 at 03:33 AM.
Reply With Quote

Sponsored Links

  #112  
Old 05-03-2010, 10:35 AM
amacman's Avatar
Member
 
Join Date: May 2008
Location: glasgow,scotland
Posts: 1,462
amacman is on a distinguished road
I added info to my previous post .
Reply With Quote
  #113  
Old 05-03-2010, 01:51 PM
StanF18's Avatar
Member
 
Join Date: Nov 2007
Location: northern NJ
Posts: 994
StanF18 is on a distinguished road
Quote:
Originally Posted by JCL View Post
I'm waiting to see the calculation of how high that cliff has to be for the terminal velocity to be a factor. I did the terminal velocity calculation, above, so I'll let someone else crunch the height calculation. I'm guessing it is up there with the highest cliff on earth, let alone the highest one that has a road to it.
What did you get for Vt? I got about 417 mph for an unladen X5M...and 455 mph for for the one with the 3 fat guys in it. I'm thinking I probably did it right, because when I re-did it for an 80 kg human in a belly-flop freefall I got 120 mph. And that's the approximate terminal velocity for a skydiver in belly flop free-fall.

(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.
Reply With Quote
  #114  
Old 05-03-2010, 07:58 PM
JCL's Avatar
JCL JCL is offline
Premier Member
 
Join Date: Mar 2005
Location: Vancouver, Canada
Posts: 11,853
JCL will become famous soon enoughJCL will become famous soon enough
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.
__________________
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
Reply With Quote
  #115  
Old 05-04-2010, 04:38 AM
Fraser's Avatar
Member
 
Join Date: Jun 2008
Location: NSW, Australia
Posts: 1,135
Fraser is on a distinguished road
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.
Reply With Quote
  #116  
Old 05-04-2010, 06:12 AM
jigaro's Avatar
Member
 
Join Date: Dec 2007
Location: Tbilisi, Georgia Miami, USA
Posts: 392
jigaro is on a distinguished road
What the hell is going on with this thread, let's close it!
__________________
---2008 X5 With All Factory Options

---2002 Black S 500 Designo Edition
Reply With Quote
  #117  
Old 05-04-2010, 04:09 PM
Rez's Avatar
Rez Rez is offline
Member
 
Join Date: Aug 2009
Location: WNY
Posts: 475
Rez is on a distinguished road
yeh this thread got jacked by bunch of geeks big time.
Reply With Quote
  #118  
Old 05-04-2010, 04:10 PM
jst2878's Avatar
Member
 
Join Date: Jan 2006
Location: The BIG Apple
Posts: 3,218
jst2878 is on a distinguished road
you need to smash your pedal to the floor a few times
__________________
2001 X5 4.4i WHITE-Loaded like a baby's diaper SOLD
Reply With Quote
  #119  
Old 05-04-2010, 05:40 PM
JCL's Avatar
JCL JCL is offline
Premier Member
 
Join Date: Mar 2005
Location: Vancouver, Canada
Posts: 11,853
JCL will become famous soon enoughJCL will become famous soon enough
Quote:
Originally Posted by Rez View Post
yeh this thread got jacked by bunch of geeks big time.


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).
__________________
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
Reply With Quote
  #120  
Old 05-04-2010, 06:01 PM
StanF18's Avatar
Member
 
Join Date: Nov 2007
Location: northern NJ
Posts: 994
StanF18 is on a distinguished road
Quote:
Originally Posted by Rez View Post
yeh this thread got jacked by bunch of geeks big time.
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!
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On





All times are GMT -4. The time now is 02:10 AM.
vBulletin, Copyright 2024, Jelsoft Enterprises Ltd. SEO by vBSEO 3.6.0
© 2017 Xoutpost.com. All rights reserved. Xoutpost.com is a private enthusiast site not associated with BMW AG.
The BMW name, marks, M stripe logo, and Roundel logo as well as X3, X5 and X6 designations used in the pages of this Web Site are the property of BMW AG.
This web site is not sponsored or affiliated in any way with BMW AG or any of its subsidiaries.