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  #91  
Old 05-01-2010, 03:48 AM
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Quote:
Originally Posted by JCL View Post
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/Cd ratio), driven off a cliff (presumably a realistic tall one). You are 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 suggest that the X5M is 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?
I know that where the discussion started but it evolved beyond that. StanF18 suggested "FORGET the mass...and the weight...M and W don't apply to the velocity in TT Bear's "X falling off a cliff" ". This could be true of the cliff is small enough. Then you suggested, "Mass cancels back out of the acceleration formulae ", which is incorrect regardless of the height of the cliff in question.
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  #92  
Old 05-01-2010, 04:12 AM
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Originally Posted by Fraser View Post
I know that where the discussion started but it evolved beyond that. StanF18 suggested "FORGET the mass...and the weight...M and W don't apply to the velocity in TT Bear's "X falling off a cliff" ". This could be true of the cliff is small enough. Then you suggested, "Mass cancels back out of the acceleration formulae ", which is incorrect regardless of the height of the cliff in question.
That was my point, in bold. My sentence about mass cancels out was just sloppy, I was trying to say that it was irrelevant.
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  #93  
Old 05-01-2010, 10:12 AM
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Originally Posted by MFL101 View Post
So, bottom line: X5M is fast...lol
....and feels fast to some.
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  #94  
Old 05-01-2010, 11:15 AM
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Jcl , I don`t think the parking sensors wiil help but maybe the adaptive cruise control thingy might help if it could deploy the airbags in time.
terminal velocity for a freefalling skydiver in stable body position (horizontal to earth ) is 120 mph , the figure 174 ft per second per second comes to mind .
depending on the altitude you begin the freefall , you could possible accelerate ad infinitum . a bloke managed to exceed mach 1 falling from a balloon at 120000 ft .is that a rush or what .
I managed to achieve about 280 mph head down from 10000ft before it was time to slow down but I messed up as it is not easy to slow at that speed due to the air pressure , I had to deploy the canopy at 2500 ft whist travelling at 200mph , this was very painful , I still remember the sound of bones compressing . the harness left serious bruising to my torso .
I wish I could remember how to explain this stuff in the way it was explained to me by the genius Skygods I learned from .
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  #95  
Old 05-01-2010, 04:30 PM
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Ummmmmmm........ wow.

Ever wonder, in retrospect, whether posting a certain way lacked a certain degree of sagacity, LOL

Seem like I have unleashed a beast. Need to brush up on my physics.

My head hurts

An intereseting, read, nonetheless, and apologies to the OP, for making this thread follow a tangential path.....
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  #96  
Old 05-01-2010, 06:11 PM
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It`s all good entertainment .
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  #97  
Old 05-01-2010, 07:31 PM
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Originally Posted by TTBear View Post
Ummmmmmm........ wow.

Ever wonder, in retrospect, whether posting a certain way lacked a certain degree of sagacity, LOL

Seem like I have unleashed a beast. Need to brush up on my physics.

My head hurts

An intereseting, read, nonetheless, and apologies to the OP, for making this thread follow a tangential path.....
My apologies to the OP as well. I figured that after 60 posts of everyone agreeing that the X5M was very fast, but that sometimes it didn't feel that fast due to the very high capabilities of the vehicle, that we had time to explore parallel themes. The cliff example (X5M vs 4.6) seemed more relevant than Scotty and the transporter.
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  #98  
Old 05-01-2010, 07:59 PM
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Quote:
Originally Posted by amacman View Post
...depending on the altitude you begin the freefall , you could possible accelerate ad infinitum
Won't happen unless you are free falling in a perfect vacuum. With freefall through the air you will reach a terminal velocity which is dependent on the density of air, the aerodynamic drag on the skydiver and the weight of the skydiver.
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  #99  
Old 05-01-2010, 08:33 PM
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I just read your wikipedia link , it says a heavier object will have a greater terminal velocity so TT Bear is correct .
there is a link there about the freefall speed record and as far as I am aware the info is wrong .
I`m sure mach 1 was exceeded years ago .
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  #100  
Old 05-01-2010, 08:44 PM
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Quote:
Originally Posted by amacman View Post
I just read your wikipedia link , it says a heavier object will have a greater terminal velocity .
That is true provided everything else (ie aero drag and the density of the medium through which the object is falling) is equal.
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