Home Forums Articles How To's FAQ Register
Go Back   Xoutpost.com > BMW SAV Forums > X ///M Forum
Arnott
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
  #81  
Old 04-30-2010, 07:06 PM
Member
 
Join Date: Feb 2010
Location: New York City
Posts: 99
MFL101 is on a distinguished road
So, bottom line: X5M is fast...lol
Reply With Quote

Sponsored Links

  #82  
Old 04-30-2010, 08:41 PM
Member
 
Join Date: Sep 2009
Location: Florida
Posts: 30
Nic941 is on a distinguished road
Bibendum ... could not agree more.
I loved my E39 M5. The X5M is better.
The soon to be M5 may be better yet, though I like the view from up here, and I'm going fast enough!

K
__________________
Reply With Quote
  #83  
Old 04-30-2010, 09:50 PM
Fraser's Avatar
Member
 
Join Date: Jun 2008
Location: NSW, Australia
Posts: 1,135
Fraser is on a distinguished road
Quote:
Originally Posted by StanF18 View Post
FORGET the mass...and the weight...M and W don't apply to the velocity in TT Bear's "X falling off a cliff" example. The only thing that matters here is the acceleration of gravity (g): 9.8 meters/second^2. This number applies to all objects regardless of their mass. The 2 variables which CAN and do lead to different falling rates is cross-sectional area and coefficient of drag (Cd).
Not right. When an object is in free fall through the atmosphere there are two forces at work. One is the gravitational pull between the earth and the object (trying to speed things up) and the other is the aerodynamic drag of the object through the atmosphere (trying to slow things down). The object reaches its steady-state velocity when these two forces are balanced.

The gravitation pull between the object and earth is not however constant but is dependent on the mass of the object (as it is also dependent on the mass of the earth).
Reply With Quote
  #84  
Old 05-01-2010, 12:12 AM
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 Fraser View Post
Not right. When an object is in free fall through the atmosphere there are two forces at work. One is the gravitational pull between the earth and the object (trying to speed things up) and the other is the aerodynamic drag of the object through the atmosphere (trying to slow things down). The object reaches its steady-state velocity when these two forces are balanced.

The gravitation pull between the object and earth is not however constant but is dependent on the mass of the object (as it is also dependent on the mass of the earth).
It seemed pretty right to me. Stan's comment about the two variables that lead to different falling rates (drag and cross sectional area) is the same as your comment about aerodynamic drag.

Not sure why the gravitational pull matters here. Mass cancels back out of the acceleration formulae.

Now, how about we put these X5 puppies on a ramp up to that cliff edge so that we can do some projectile calculations and see how far they can go before they impact? And will 98 RON fuel make the X5M go farther? And most importantly, will the PDC alert the driver to impending impact if the driver turns it on mid-flight?
__________________
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
  #85  
Old 05-01-2010, 12:32 AM
Fraser's Avatar
Member
 
Join Date: Jun 2008
Location: NSW, Australia
Posts: 1,135
Fraser is on a distinguished road
Think about this. Two objects. One is a large and very fine bird feather. The other is a moulding of that same feather made from lead. Same shape, same cross-sectional area, same cd. When you drop them together from a good height which will hit the ground first?

Hopefully the link below works. If gives a formula for terminal velocity. Shows how mass and therefore gravitational pull is a factor.

Terminal velocity - Wikipedia, the free encyclopedia

Last edited by Fraser; 05-01-2010 at 12:51 AM.
Reply With Quote
  #86  
Old 05-01-2010, 01:09 AM
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 Fraser View Post
Think about this. Two objects. One is a large and very fine bird feather. The other is a moulding of that same feather made from lead. Same shape, same cross-sectional area, same cd. When you drop them together from a good height which will hit the ground first?
While I understand the concept of terminal velocity, I am not sure I understand the relevance in a discussion of the falling speeds of different versions of the X5. Are you saying that the E53 is a feather? Or that the E70 is a lead sled?
__________________
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
  #87  
Old 05-01-2010, 01:25 AM
Fraser's Avatar
Member
 
Join Date: Jun 2008
Location: NSW, Australia
Posts: 1,135
Fraser is on a distinguished road
Regardless of X5s of any variety falling off cliffs, mass plays a part in the terminal velocity of a free-falling object.
Reply With Quote
  #88  
Old 05-01-2010, 02:41 AM
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
Using published figures for the X5M (2380 kg, frontal area of 2.9 sq m, drag coefficient of 0.38, and assuming the density of air to be 1.2 kg/cubic meter), I calculated a terminal velocity for the X5M (falling headlights first) of 188 m/s, or 420 miles per hour. I am not sure how high this cliff is, but it must be one hell of a drop for the terminal velocity to be a factor.

(Sorry Weasel, but I ignored buoyancy effects).

Hey, it's a slow night. Bottom line? MFL101 was right, the X5M is fast, and even faster if dropped off a very high cliff.

Corrections are most welcome from those engineers or aerodynamicists who took this more recently than 30 years ago, or who just remember it better.
__________________
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
  #89  
Old 05-01-2010, 02:49 AM
Fraser's Avatar
Member
 
Join Date: Jun 2008
Location: NSW, Australia
Posts: 1,135
Fraser is on a distinguished road
Nice argument JCL but you are avoiding the key question; ie does weight play a part in free-fall. You have argued for the negative for reasons I can't understand. You know better than that.

PS: The cliff is high, very high.
Reply With Quote
  #90  
Old 05-01-2010, 03:35 AM
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 Fraser View Post
Nice argument JCL but you are avoiding the key question; ie does weight play a part in free-fall. You have argued for the negative for reasons I can't understand. You know better than that.

PS: The cliff is high, very high.
The discussion wasn't about free-fall in general terms, it was about two X5 models with an assumed equal Cd, and therefore a very similar weight/drag ratio), driven off a cliff (presumably a realistically tall one). I understood that you were arguing that the one with the three guys in it gets to the ground faster (because of the increased mass and therefore the increased gravitational pull). Some have suggested that the X5M is somewhat heavy, but are we comparing it to a planetary body?

PS: How high does the cliff have to be for the X5M to reach terminal velocity?
__________________
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

Last edited by JCL; 05-01-2010 at 03:40 AM.
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 04:53 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.