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Old 12-07-2006, 11:24 AM   #31
Kitsune
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That's awesome, UT!
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Old 12-07-2006, 11:27 AM   #32
Flint
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Quote:
Originally Posted by glatt
The question doesn't say that.
Yes it does:

Quote:
Originally Posted by Kitsune
A plane is standing on a runway that can move, like a giant treadmill. When the plane's engines throttle up, it begins to move forward, but the treadmill is made to match the forward speed of the plane, only in the opposite direction. So, as the plane moves forward, it moves backwards beneath the aircraft.
It matches the forward speed, cancelling all forward motion. UT's animation repeatedly says "as the plane moves forward" but that is not the scope of what we are discussing. We are discussing a stationary plane.

Fuck the wheels, fuck the treadmill, fuck the thrust. Lift is produced by air moving across the wings. Moving.
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Old 12-07-2006, 11:28 AM   #33
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I found it after googling for the problem... turns out it was fought over by folks on a physics board, so I feel a little less foolish...
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Old 12-07-2006, 11:34 AM   #34
dar512
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Flint. The wheels don't matter as far as forward motion is concerned. As the graphic that UT says, the wheels will just spin twice as fast. It doesn't matter how fast the treadmill is going backward, because the plane's pushing against the air, not the ground.
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Old 12-07-2006, 11:35 AM   #35
Shawnee123
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(Not being sarcastic...I find this debate fascinating)
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Old 12-07-2006, 11:39 AM   #36
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Quote:
Originally Posted by dar512
Flint. The wheels don't matter as far as forward motion is concerned. As the graphic that UT says, the wheels will just spin twice as fast. It doesn't matter how fast the treadmill is going backward, because the plane's pushing against the air, not the ground.
Fuck how fast the wheels are spinning. No forward motion = no lift.

The only item of discussion here is how you read the question. Stationary planes (commercial jetliners) do not jump into the air. Ever.
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Old 12-07-2006, 11:42 AM   #37
dar512
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Quote:
Originally Posted by Kitsune
So, as the plane moves forward, it moves backwards beneath the aircraft.
If I understand you, the above part of the problem set means "no forward motion" to you. I don't think it does. It would for a car. It doesn't for a plane.
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Old 12-07-2006, 11:46 AM   #38
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Quote:
Originally Posted by dar512
If I understand you, the above part of the problem set means "no forward motion" to you.
It doesn't mean that to me. I would say there is most certainly forward motion in the way I described it. The wheels are free spinning despite the treadmill.
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Old 12-07-2006, 11:48 AM   #39
Flint
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Quote:
Originally Posted by dar512
If I understand you, the above part of the problem set means "no forward motion" to you.
No, this part does:
Quote:
...the treadmill is made to match the forward speed of the plane, only in the opposite direction.
There aren't two different reasons for the wheels to spin. They only ever spun because the plane was trying to move forward, and the treadmill matches the forward speed, cancelling it. If the plane thrusts harder, the treadmill continues to cancel it's motion. There is no tip-over point, here. The treadmill prevents the plane from moving. The plane cannot take off from a stationary position.
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There's a level of facility that everyone needs to accomplish, and from there
it's a matter of deciding for yourself how important ultra-facility is to your
expression. ... I found, like Joseph Campbell said, if you just follow whatever
gives you a little joy or excitement or awe, then you're on the right track.
. . . . . . . . . . . . . . . . . . . . . . . . . . Terry Bozzio
Last edited by Flint; 12-07-2006 at 11:52 AM.
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Old 12-07-2006, 11:52 AM   #40
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Quote:
Originally Posted by Flint
If the plane thrusts harder, the treadmill continues to cancel it's motion. There is no tip-over point, here.
Get a motorized treadmill and a bicycle. Hold the bicycle in place and turn the treadmill up as high as it will go. Are you having to fight very much to keep the bike stationary? No -- the friction between the bike frame and wheels is very low. Now, push the bike forward. Is it taking much effort? Not at all.
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Old 12-07-2006, 11:56 AM   #41
Flint
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Quote:
Originally Posted by Kitsune
Now, push the bike forward. Is it taking much effort? Not at all.
Quote:
...the treadmill is made to match the forward speed of the plane, only in the opposite direction.
It doesn't matter how "hard" it is. In this scenario, you can't do that.
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. . . . . . . . . . . . . . . . . . . . . . . . . . Terry Bozzio
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Old 12-07-2006, 11:56 AM   #42
Happy Monkey
I think this line's mostly filler.
 
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The plane will move forward, no matter how fast the treadmill is going. The treadmill can't cancel the forward motion of the plane, because the plane's speed is not determined by the wheels. If you hold a hotwheel car in your hand, and put it on a treadmill, you can move it forward no matter how fast the treadmill is going. Likewise, the jet engine will move the plane forward no matter what the treadmill and wheels are doing.

Now, if it were in a wind tunnel, and air was blown to cancel the jet engines, that would be a different story.
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Old 12-07-2006, 11:58 AM   #43
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You're right: if you ignore the question you can get whatever answer you want.
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There's a level of facility that everyone needs to accomplish, and from there
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expression. ... I found, like Joseph Campbell said, if you just follow whatever
gives you a little joy or excitement or awe, then you're on the right track.
. . . . . . . . . . . . . . . . . . . . . . . . . . Terry Bozzio
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Old 12-07-2006, 12:04 PM   #44
Happy Monkey
I think this line's mostly filler.
 
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Nothing in the question says the plane is stationary. Just that the treadmill moves. But the treadmill can not stop the plane! The assumption that the plane is made stationary by the treadmill is something that you are bringing in, and is the trick part of this trick question.
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Old 12-07-2006, 12:06 PM   #45
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http://www.straightdope.com/columns/060203.html
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