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Old 12-07-2006, 02:23 PM   #1
Flint
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Quote:
Originally Posted by Happy Monkey
It is not possible for the speed of a treadmill to affect the speed of the plane (short of mechanical failure in the wheels).
It doesn't have to, and I never said it did. Where did you get that?
Quote:
Originally Posted by Happy Monkey
You must assume that the plane is moving forward relative to the ground, and the treadmill is moving backward at the same speed, relative to the ground.
If the treadmill matches the forward speed of the plane, the plane cannot "begin" to move forward, except relative to the treadmill.
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Old 12-07-2006, 02:38 PM   #2
Happy Monkey
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Quote:
Originally Posted by Flint
It doesn't have to, and I never said it did. Where did you get that?
When you said that they could cancel each other out. That is not physically possible.
Quote:
If the treadmill matches the forward speed of the plane, the plane cannot "begin" to move forward, except relative to the treadmill.
The treadmill is moving backward relative to the ground at speed X. The plane is moving forward, relative to the ground, at speed X. The plane is moving at speed 2X relative to the treadmill. Your interpretation is not physically possible.
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Old 12-07-2006, 02:41 PM   #3
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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.
No. It doesn't. All it says is that the treadmill moves backward as fast as the plane moves forward.
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Old 12-07-2006, 03:04 PM   #4
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Hope this comes through. Never thought I'd see such excitement about a physics problem!
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Old 12-07-2006, 03:08 PM   #5
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That's a nice drawing, but the belt force arrow is in the wrong spot. It applies force to the surface of the weel's tire, not the axle.
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Old 12-07-2006, 03:10 PM   #6
Flint
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Quote:
Originally Posted by glatt
That's a nice drawing, but the belt force arrow is in the wrong spot.
Which doesn't matter, because the question states what the result is, not "how" it works.
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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
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Old 12-07-2006, 03:19 PM   #7
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Quote:
Originally Posted by Flint
Which doesn't matter, because the question states what the result is, not "how" it works.
What? Is this the line you're having problems with?

Quote:
So, as the plane moves forward, it moves backwards beneath the aircraft.
Because it absolutely does not mean "...as the plane moves forward, the plane moves backwards beneath the aircraft", if that is what you're thinking. Context, man, context.
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Old 12-07-2006, 03:08 PM   #8
Flint
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Quote:
Originally Posted by Pie
Never thought I'd see such excitement about a physics problem!
All the excitement, in this thread, is regarding a semantics problem.
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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
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Old 12-07-2006, 03:17 PM   #9
Happy Monkey
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And the stated result is that the plane moves forward.
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Old 12-07-2006, 04:02 PM   #10
Undertoad
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Is it the word "but" that confuses? Drop the word "but" in the original question and replace it with the word "and". The conjunction does not change the meaning of the question.
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Old 12-07-2006, 04:08 PM   #11
SteveDallas
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OK, let's try this one. The engine is not on at all. The plane is just sitting there. Now the treadmill/runway starts to turn, let's say at 10 MPH. What happens to the plane?
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Old 12-07-2006, 04:09 PM   #12
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Quote:
Originally Posted by SteveDallas
OK, let's try this one. The engine is not on at all. The plane is just sitting there. Now the treadmill/runway starts to turn, let's say at 10 MPH. What happens to the plane?
Friction or no friction?
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Old 12-07-2006, 04:09 PM   #13
Kitsune
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Quote:
Originally Posted by SteveDallas
OK, let's try this one. The engine is not on at all. The plane is just sitting there. Now the treadmill/runway starts to turn, let's say at 10 MPH. What happens to the plane?
It moves backwards because of friction. The important aspect here is that it takes very little force to overcome this friction because the wheels roll.
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Old 12-07-2006, 04:11 PM   #14
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In Steve's scenario, the plane moves along with the runway if there is friction, and it stays stationary if there is no friction.
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Old 12-07-2006, 04:13 PM   #15
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It's physics class so let's ignore friction.
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