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20 Dec 2006, 17:27
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#51
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The Twilight of the Gods
Join Date: Jan 2001
Posts: 23,481
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Re: A Plane Problem
Quote:
Originally Posted by Tomkat
I can't really emphasise my argument without repeating myself again and again so :shrug: .
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You don't have an argument. You just state it won't happen.
I have an argument. You can't have read it, because it really was very simple.
Quote:
Originally Posted by Tomkat
I found this though:
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He's wrong, as I proved on the previous page.
Come on guys, MATHS IS NOT OPINION BASED.
[edit]
If you want to make an argument for your position, explain why the plane would be stationary. Don't just say that it is.
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20 Dec 2006, 17:39
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#52
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Next goal wins!
Join Date: Sep 2000
Location: London
Posts: 5,406
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Re: A Plane Problem
The plane will not remain stationary, it will take off.
\o/
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bastard bastard bastard bastard
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20 Dec 2006, 18:03
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#53
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:alpha:
Join Date: May 2002
Location: London, UK
Posts: 7,871
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Re: A Plane Problem
After a lengthy discussion with Mark being very patient and understanding ( ) I now see his point.
The thing is that most of the people agreeing with him (Ste and a few others) aren't actually saying the same thing as him...
The way I imagined it (for those stupid enough to agree with me!) is that the runway isn't necessarily tarmac. Imagine it as a big block of ice that the plane is moving against. Eventually the plane will speed up and take off (assuming that the treadmill is long enough).
When I said it didn't take off I assumed there was enough friction exerted constantly against the plane to keep it stationary. The question doesn't mention friction so you can't assume that really.
__________________
"There is no I in team, but there are two in anal fisting"
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20 Dec 2006, 18:06
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#54
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The Twilight of the Gods
Join Date: Jan 2001
Posts: 23,481
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Re: A Plane Problem
A plane will take off faster than usual from a big block of ice. The wheels are only there to reduce the friction against the tarmac, and ice has less friction than tarmac.
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20 Dec 2006, 18:09
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#55
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so f*cking zen
Join Date: Jan 2003
Location: Hitting Bottom
Posts: 8,499
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Re: A Plane Problem
The plane doesnt move (in relation to a fixed point to the side of the treadmill) so there's no lift so it doesn't take off.
IMO anyways.
__________________
On a long enough timeline, the survival rate for everyone drops to zero.
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20 Dec 2006, 18:10
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#56
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:alpha:
Join Date: May 2002
Location: London, UK
Posts: 7,871
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Re: A Plane Problem
Quote:
Originally Posted by MrL_JaKiri
A plane will take off faster than usual from a big block of ice. The wheels are only there to reduce the friction against the tarmac, and ice has less friction than tarmac.
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Look bucko I only just agreed with you about it taking off AT ALL. Don't push your luck about it taking off fast or slow or whatever.
__________________
"There is no I in team, but there are two in anal fisting"
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20 Dec 2006, 18:21
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#57
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so f*cking zen
Join Date: Jan 2003
Location: Hitting Bottom
Posts: 8,499
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Re: A Plane Problem
Tom you started off correct and now it's all gone terribly wrong for you ... ;'(
__________________
On a long enough timeline, the survival rate for everyone drops to zero.
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20 Dec 2006, 18:37
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#58
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Rawr rawr
Join Date: Dec 2000
Location: Upside down
Posts: 5,300
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Re: A Plane Problem
This thread sucks.
It started with a silly trick question, and now we're at a point where people start throwing in formula's and Tomkat is totally losing it.
World wars have been fought over less!
__________________
"Yay"
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20 Dec 2006, 19:04
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#59
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:alpha:
Join Date: May 2002
Location: London, UK
Posts: 7,871
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Re: A Plane Problem
Quote:
Originally Posted by Dace
Tom you started off correct and now it's all gone terribly wrong for you ... ;'(
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I did, but only if you assume the treadmill is made of something that provides enough friction to keep the plane stationary on it (tarmac would do). If you think about it though, if the treadmill is made of something like ice or glass or something, then the plane would eventually gather enough momentum to start accelerating.
Obviously you are meant to assume that it DOES have enough friction (which is what my entire argument was based on). As it doesn't say that though, we can't assume it.
I wasn't wrong, but I also wasn't right, as I assumed things that shouldn't be assumed.
__________________
"There is no I in team, but there are two in anal fisting"
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20 Dec 2006, 19:18
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#60
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The Twilight of the Gods
Join Date: Jan 2001
Posts: 23,481
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Re: A Plane Problem
Quote:
Originally Posted by Tomkat
I wasn't wrong
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Yes you were, the maths post on the last page showed that.
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20 Dec 2006, 20:02
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#61
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Henry Kelly
Join Date: Apr 2000
Posts: 7,374
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Re: A Plane Problem
So is the gist of this that provided the surface of the treadmill doens't provide sufficient friction to keep the plane stationary, i.e. if the surface moved backwards one meter the plane would move backwards some amount less than that, then the plane could accelerate down the treadmill surface, attain enough speed to take off and then take off? Or have I gotten totally the wrong end of this retarded stick?
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You're now playing ketchup
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20 Dec 2006, 20:14
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#62
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break it down!
Join Date: Feb 2005
Posts: 2,087
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Re: A Plane Problem
Thats what I understand Pablissimo, although it looks like Jakiri is arguing that even with the surface of the treadmill having enough friction to keep the plane stationary, it would take off.
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I put the sex in dyslexia!
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20 Dec 2006, 20:16
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#63
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Henry Kelly
Join Date: Apr 2000
Posts: 7,374
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Re: A Plane Problem
Well by the treadmill I was meaning the interface between the treadmill and the 'wheels' I guess. So the planes axels would have to be locked, the rubber on the tires have infinite friction with with treadmill.
I'm clearly just not getting this if that's wrong.
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You're now playing ketchup
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20 Dec 2006, 20:17
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#64
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:alpha:
Join Date: May 2002
Location: London, UK
Posts: 7,871
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Re: A Plane Problem
Quote:
Originally Posted by MrL_JaKiri
Yes you were, the maths post on the last page showed that.
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I think that for the purpose of the poorly worded question, we aren't supposed to take friction into account. Just the idea of a plane moving forward and being pulled back at the same time.
I was right if we assume the friction is high enough to prevent the plane from moving forward. What Ste and others thought is that the plane could still take off from the thrust in its engines, even though it wouldn't be moving anywhere. Which it couldn't :crymeariver:
__________________
"There is no I in team, but there are two in anal fisting"
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20 Dec 2006, 20:19
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#65
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:alpha:
Join Date: May 2002
Location: London, UK
Posts: 7,871
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Re: A Plane Problem
Quote:
Originally Posted by Ste
Imagine you have a toy plane that you are holding onto a conveyor. The wheels are moving but the plane is not. If you push the plane forwards it will move. In this case your hands are forward force that in reality would be the engines.
It doesn't matter how fast the conveyor is going - it doesn't affect the plane. Just the wheels.
If the plane is moving forward there is air moving over the wings. Hence it is possible to fly.
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This is a silly example.
According to your original problem, the conveyor would be moving at the same speed as the wheels of the toy plane. So no matter how hard I pushed it, the wheels would speed up but the conveyor would also speed up. So the toy plane would stay still, with my puffing and huffing and pushing it.
__________________
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20 Dec 2006, 20:19
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#66
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Mr. Blobby
Join Date: Nov 2000
Location: Belgium
Posts: 8,271
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Re: A Plane Problem
An airplane is powered by it's engines which give the vehicle forwards motion in relation to the air around the craft. Since the treadmill does not affect the air, the airplane will move forward just fine and take off - the wheels will merely be rotating at twice the speed the aircraft is moving.
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20 Dec 2006, 20:23
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#67
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The Twilight of the Gods
Join Date: Jan 2001
Posts: 23,481
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Re: A Plane Problem
Quote:
Originally Posted by _Kila_
Thats what I understand Pablissimo, although it looks like Jakiri is arguing that even with the surface of the treadmill having enough friction to keep the plane stationary, it would take off.
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Actually, it's the speed of the treadmill that matters. Because the wheels aren't slipping on the tarmac, as long as the surface is not actually sticky and just posessing high coefficients of friction the friction will be constant with surfaces with higher frictions, and the friction will just be the friction between the wheel and the axel. It's how wheels work.
Quote:
Originally Posted by Tomkat
I was right if we assume the friction is high enough to prevent the plane from moving forward.
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No you weren't. The maths on the last page proved that.
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20 Dec 2006, 20:25
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#68
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Mr. Blobby
Join Date: Nov 2000
Location: Belgium
Posts: 8,271
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Re: A Plane Problem
Quote:
Originally Posted by Tomkat
This is a silly example.
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No, it's a perfectly fine example.
When you put a toy car against a wall, the force that keeps it to the wall or makes it move up and down alongside it, is your hand. The wheels are merely rotating against the wall as a result of you moving the body of the car, in exactly the same way an airplane's wheels only move as a result of the engines moving the craft across the surface.
Even if you were to put up a toy car against a vertical conveyor belt running downwards, you would still be able to overcome the friction between the wheels and the belt, and move the car upwards, even though the wheels would be spinning like crazy.
Quote:
According to your original problem, the conveyor would be moving at the same speed as the wheels of the toy plane.
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No, according to the original problem, the conveyor belt moves at the same speed as the aircraft does; not at the same speed it's wheels are rotating.
Edit: Changed wording of what Mark quoted; obviously the wheels are moving at the same speed as the aircraft since they're attached to it, they're merely rotating at twice the speed that is consistent with the aircraft's velocity.
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20 Dec 2006, 20:28
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#69
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The Twilight of the Gods
Join Date: Jan 2001
Posts: 23,481
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Re: A Plane Problem
Quote:
Originally Posted by Leshy
No, according to the original problem, the conveyor belt moves at the same speed as the aircraft does; not at the same speed it's wheels do.
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Which, as I said on the last page, in and of itself proves that you can't stop the airplane taking off, as the interpretation is inconsistent with "Treadmill going so fast that the plane stops". I prefer to think of it as the wheels though, because it reduces the "But it's obviously this, and no amount of argument will persuade me!" things TK was and is doing.
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20 Dec 2006, 20:29
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#70
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:alpha:
Join Date: May 2002
Location: London, UK
Posts: 7,871
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Re: A Plane Problem
Quote:
Originally Posted by Leshy
Even if you were to put up a toy car against a vertical conveyor belt running downwards, you would still be able to overcome the friction between the wheels and the belt, and move the car upwards, even though the wheels would be spinning like crazy.
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You wouldn't be able to if that conveyor belt was moving at 1000 mph (for example). You'd just be scraping the car down the conveyor belt and its wheels would be stationary.
Quote:
Originally Posted by Leshy
No, according to the original problem, the conveyor belt moves at the same speed as the aircraft does; not at the same speed it's wheels do.
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So even if the wheels were stationary (as stated above) the aircraft couldn't go faster than the conveyor belt.
__________________
"There is no I in team, but there are two in anal fisting"
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20 Dec 2006, 20:33
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#71
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Kwaak
Join Date: Mar 2002
Location: Netherlands
Posts: 296
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Re: A Plane Problem
Think about it like this, how would an airplane gain speed when in the air? Is it that different from gaining that speed on the ground? It doens't NEED the ground to go forward.
The only way it is possible for the plane to stay on the exact same spot is to put the weels on their handbrake. That way there's a chance it will create enough friction with the conveyer belt for the plane to essentially 'stay still'.
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20 Dec 2006, 20:34
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#72
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Mr. Blobby
Join Date: Nov 2000
Location: Belgium
Posts: 8,271
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Re: A Plane Problem
Quote:
Originally Posted by Tomkat
You wouldn't be able to if that conveyor belt was moving at 1000 mph (for example).
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Sure I would. The speed of the conveyor belt is completely irrelevant. Even if it ran at a speed of 10.000mph, I'd have little trouble holding a toy car against it, or even moving it in the opposite direction of the conveyor belt.
Quote:
So even if the wheels were stationary (as stated above) the aircraft couldn't go faster than the conveyor belt.
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The original problem specifically states that the conveyor belt runs as fast as the aircraft, so it will be speeding up along with the aircraft until the latter takes off.
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20 Dec 2006, 20:39
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#73
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:alpha:
Join Date: May 2002
Location: London, UK
Posts: 7,871
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Re: A Plane Problem
Quote:
Originally Posted by paolo
Think about it like this, how would an airplane gain speed when in the air? Is it that different from gaining that speed on the ground? It doens't NEED the ground to go forward.
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This doesn't debunk the counterargument of it being stationary at all.
__________________
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20 Dec 2006, 20:44
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#74
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Mr. Blobby
Join Date: Nov 2000
Location: Belgium
Posts: 8,271
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Re: A Plane Problem
Quote:
Originally Posted by Tomkat
This doesn't debunk the counterargument of it being stationary at all.
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Quote:
Originally Posted by Leshy
An airplane is powered by it's engines which give the vehicle forwards motion in relation to the air around the craft. Since the treadmill does not affect the air, the airplane will move forward just fine and take off - the wheels will merely be rotating at twice the speed the aircraft is moving.
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20 Dec 2006, 20:48
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#75
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USS Oklahoma
Join Date: Jun 2005
Posts: 2,500
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Re: A Plane Problem
Airplanes take off based on lift created by the passage of air over the wings. Air speed, not ground speed determines the point at which an airplane takes off.
Propeller planes gain airspeed by screwing through the air, pulling the plane forward. Jet engines gain airspeed by pushing the plane through the air. Aircraft carriers launch their planes through a combination of catapult and jet engine to get airspeed.
The ground is irrelevant except for the fact that the plane must take off from some surface.
The problem in the hypothetical is that the wheels and treadmill are irrelevant. A better question would be what if there was a giant wind machine behind the plane that increased exactly as the plane's thurst increased. If it did, the airplane could achieve any ground speed and still not be able to take off.
There is a reason why airports have runways facing in different directions and swithch the airplanes around so that, as far as practical, airplanes take off and land heading into the wind. Aircraft carriers always turn into the wind to launch or recover aircraft.
Also, if the head wind is sufficient, the plane could take off from a stationary start, it would seem. This is the principal upon which the wind tunnel is based.
__________________
Ignorance is curable, stupidity is not.
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20 Dec 2006, 20:53
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#76
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Fightin-irish for life
Join Date: Mar 2001
Location: guinness brewery
Posts: 2,177
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Re: A Plane Problem
if the threadmill is matchign the motion of the planes wheels it wont take off as it has no forward thrust from the engines , the threadmill absorbs the energy released from the engines by matching the motion of the wheels
__________________
Ascendancy, now with added Irish
"In the absence of orders, find something and kill it."
-Rommel
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20 Dec 2006, 20:54
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#77
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The Twilight of the Gods
Join Date: Jan 2001
Posts: 23,481
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Re: A Plane Problem
Quote:
Originally Posted by Tomkat
This doesn't debunk the counterargument of it being stationary.
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You claiming that "it being stationary" is a counterargument doesn't debunk the counterargument that talk of it being stationary or not is a conclusion, not axiomatic as you seem to think.
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20 Dec 2006, 21:02
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#78
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USS Oklahoma
Join Date: Jun 2005
Posts: 2,500
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Re: A Plane Problem
Quote:
Originally Posted by gzambo
if the threadmill is matchign the motion of the planes wheels it wont take off as it has no forward thrust from the engines , the threadmill absorbs the energy released from the engines by matching the motion of the wheels
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The motion of the treadmill whouldn't stop the thrust of the engine against the air. The treadmill would have to move, not just the surface of it, but the entire treadmill. The plane would be probelled forward in relationship to the air not the ground. The ground actually slows the plane down. The treadmill would have to move over the ground, itself at a speed sufficient to keep the airplane stationary to the air not the ground. Then of course you wouldn't have a treadmill, you would have a sled.
For the thought that the treadmill would keep it from getting airborne then the opposite must be true. If you put a plane on a tread mill with its engines off, then it should leap into the air at the point that the treadmill is going fast enough.
__________________
Ignorance is curable, stupidity is not.
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20 Dec 2006, 21:08
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#79
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Miles Teg
Join Date: Nov 2001
Location: Dom City
Posts: 5,192
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Re: A Plane Problem
Okay, better answer:
friction = 0
if there is no friction, it doesn't matter on what kind of treadmill, rollerblade, ice, tarmaq or whatever it is moving, since it will only stop the body of the plane from crashing into the ground, then it will simply take off using normal power.
friction = 1 (meaning all power of the treadmill is transferred to the plane, countering any propulsion), no airflow -> no take off
0 < friction < 1,
the plane accelerates slowly and will or reach the end of the treadmill before reaching the critical speed to take off or will take off before it will reach the end of the treadmill
__________________
Audentes Fortuna Iuvat
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20 Dec 2006, 21:36
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#80
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The Twilight of the Gods
Join Date: Jan 2001
Posts: 23,481
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Re: A Plane Problem
Quote:
Originally Posted by Knight Theamion
Okay, better answer:
friction = 0
if there is no friction, it doesn't matter on what kind of treadmill, rollerblade, ice, tarmaq or whatever it is moving, since it will only stop the body of the plane from crashing into the ground, then it will simply take off using normal power.
friction = 1 (meaning all power of the treadmill is transferred to the plane, countering any propulsion), no airflow -> no take off
0 < friction < 1,
the plane accelerates slowly and will or reach the end of the treadmill before reaching the critical speed to take off or will take off before it will reach the end of the treadmill
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You don't understand either how friction works or how wheels work.
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20 Dec 2006, 21:47
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#81
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Registered User
Join Date: Jan 2003
Posts: 4,290
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Re: A Plane Problem
__________________
im not tolerant, i just dont care.
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20 Dec 2006, 21:49
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#82
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Victim of Marriage
Join Date: Oct 2005
Location: NW Indiana
Posts: 784
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Re: A Plane Problem
I can't believe I just read this whole thread.
Say that the treadmill is of sufficient material it creates enough friction that the wheels would match it's speed, and that the wind speed is 0.
I would say that it wouldn't take off, despite the thrust of the engines.
If it's a propeller plane, say fixed on the front, it's only pulling the air along the fuselage of the plane, and not the wings. So no matter how much thrust it was generating, and pulling the plane, it's merely only pulling it as fast as the treadmill is keeping up with it, therefore you have no airflow under the wings, and the plane will not take off.
For a jet enginee, it's basically the same principle, the air being sucked into the engines is only being sucked into the engines, it doesn't create a significant amount of airflow to the wings to actually influence whether or not the plane will take off. If the treadmill is keeping up with the speed of the plane to where there is no forward movement on the ground, dispite the amount of thrust generated by the engines, you have no airflow, and thus can't take off.
You would also have to consider that the treadmill is completely flat surface with no bumps, as any little bump would allow the plane to lift from the treadmill and gain forward movement.
__________________
You mean there's life outside the internet...oh man I'm screwed.
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20 Dec 2006, 21:53
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#83
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The Twilight of the Gods
Join Date: Jan 2001
Posts: 23,481
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Re: A Plane Problem
Quote:
Originally Posted by jt25man
I would say that it wouldn't take off, despite the thrust of the engines.
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The maths disagrees, as does common sense.
Quote:
Originally Posted by wu_trax
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Settle what exactly?
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20 Dec 2006, 22:18
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#84
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Ensign
Join Date: Aug 2005
Posts: 116
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Re: A Plane Problem
As others have said, the problem lies in the definition of the problem: If the treadmill is allowed to run fast enough to create a friction force equal to the engine's force than the plane should stay at its position, otherwise it should move.
I think the description in the first post results in the latter.
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20 Dec 2006, 22:21
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#85
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:alpha:
Join Date: May 2002
Location: London, UK
Posts: 7,871
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Re: A Plane Problem
Quote:
Originally Posted by MrL_JaKiri
The maths disagrees, as does common sense.
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"The maths disagrees" doesn't really hold much water when you say it, as it isn't a standard "plane on treadmill" formula which we can all accept. It's just a load of reasons and formulae you gave, and then expected us all to believe you.
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"There is no I in team, but there are two in anal fisting"
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20 Dec 2006, 22:35
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#86
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Banned
Join Date: May 2001
Location: Further to the right
Posts: 19,441
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Re: A Plane Problem
Quote:
Originally Posted by Ste
Some of you have probably seen this before.
"A plane equipped with fixed horizontal engines and wheel landing gear is placed on a huge treadmill runway. The treadmill has a clever design and always matches the speed of the plane, but runs in the opposite direction. Will the plane take off and fly or not?"
A crappy diagram
It's confused me for a while but I think I have my answer...
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Flight is impossible you blaspheming infidel. Maybe you should go jump off a cliff and flap your arms comrade
__________________
Some might ask what good is life without purpose but I'm anticipating a good lunch.
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20 Dec 2006, 22:40
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#87
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The Twilight of the Gods
Join Date: Jan 2001
Posts: 23,481
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Re: A Plane Problem
Quote:
Originally Posted by Tomkat
"The maths disagrees" doesn't really hold much water when you say it, as it isn't a standard "plane on treadmill" formula which we can all accept. It's just a load of reasons and formulae you gave, and then expected us all to believe you.
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How dare you suggest that the maths disagrees when all you put was a load of mathematical arguments that support the statement
I'm not exactly sure where you're having the problem with the expanation. It's all addition except at one point you have to multiply by two. It's not some arcane reasonings I put down, the fact that you're seemingly oblivious to the parts where I explain what's going on at each step is gradually convincing me I'm living in some kind of nightmarish dream world of nightmare dreams.
Meanwhile, PHYSICS PROBLEM SOLVED USING MATHS is a piece of investigative reporting that'll probably net you some kind of award.
[edit]
I forgot what confused me most. ""The maths disagrees" doesn't really hold much water when you say it"
What the hell are you going on about?
Last edited by MrL_JaKiri; 20 Dec 2006 at 22:46.
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20 Dec 2006, 22:56
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#88
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Victim of Marriage
Join Date: Oct 2005
Location: NW Indiana
Posts: 784
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Re: A Plane Problem
Quote:
Originally Posted by MrL_JaKiri
...as does common sense.
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Common sense dictates that no airflow under the wing regardless of thrust = no lift, therefore you can't get the plane off the ground.
Edit: Thrust is the force that moves the plane, thrust does not create airflow it the object is stationary due to the treadmill counteracting the thrust, regardless of how fast the wheels are going.
__________________
You mean there's life outside the internet...oh man I'm screwed.
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20 Dec 2006, 23:00
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#89
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Mr. Blobby
Join Date: Nov 2000
Location: Belgium
Posts: 8,271
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Re: A Plane Problem
Quote:
Originally Posted by jt25man
If the treadmill is keeping up with the speed of the plane to where there is no forward movement on the ground, dispite the amount of thrust generated by the engines, you have no airflow, and thus can't take off.
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Except that the treadmill will not keep the plane stationary at all, the plane will move forward normally, creating airflow and thus lift-off.
Quote:
Originally Posted by Opi
If the treadmill is allowed to run fast enough to create a friction force equal to the engine's force
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The speed of the treadmill is clearly defined in the original statement. Additionally, the treadmill running faster does not increase the amount of friction between the treadmill and the wheels.
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20 Dec 2006, 23:02
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#90
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The Twilight of the Gods
Join Date: Jan 2001
Posts: 23,481
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Re: A Plane Problem
Quote:
Originally Posted by jt25man
Common sense dictates that no airflow under the wing regardless of thrust = no lift, therefore you can't get the plane off the ground.
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Noone is arguing that no airflow produces lift. What is being argued is that the setup of the question is incapable of producing a circumstance when a plane that's not completely stationary has no airflow.
Quote:
Originally Posted by Leshy
The speed of the treadmill is clearly defined in the original statement. Additionally, the treadmill running faster does not increase the amount of friction between the treadmill and the wheels.
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It will increase the friction between the wheels and the axel, however. Having said that, the area where that would relevent is one where the simple model breaks down, and we'd have to take into account things like energy loss through the wheels and warping due to temperature.
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20 Dec 2006, 23:08
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#91
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Mr. Blobby
Join Date: Nov 2000
Location: Belgium
Posts: 8,271
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Re: A Plane Problem
Quote:
Originally Posted by MrL_JaKiri
It will increase the friction between the wheels and the axel, however.
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By the time the speed of the threadmill is of such height as to make the friction between the wheel and axel large enough to overcome the plane's thrust, the airplane has already taken off, given the fact that the threadmill moves at the same speed as the aircraft does.
Additionally, the wheelcasing would likely be torn apart before said friction gets that high.
Edit: Whee, multiple edits.
Last edited by Leshy; 20 Dec 2006 at 23:16.
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20 Dec 2006, 23:09
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#92
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The Twilight of the Gods
Join Date: Jan 2001
Posts: 23,481
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Re: A Plane Problem
Quote:
Originally Posted by Leshy
I reckon the whole wheelcasing would be torn apart before the point is reached where the friction between the wheel and the axel becomes large enough to negate the airplane's full thrust.
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Yeah, the torque on the undercarriage will be a not insignificant factor too.
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20 Dec 2006, 23:11
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#93
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Klaatu barada nikto
Join Date: Mar 2000
Location: St. Paul, Minnesota
Posts: 3,237
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Re: A Plane Problem
Quote:
Originally Posted by gzambo
if the threadmill is matchign the motion of the planes wheels it wont take off as it has no forward thrust from the engines , the threadmill absorbs the energy released from the engines by matching the motion of the wheels
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I don't see how that's possible.
A large jetliner generates several hundred thousand of pounds of thrust. The drag due to the tires is a few tens of thousands of pounds. If I'm recalling my physics correctly, the drag force due to rolling friction is equal to the coefficient of rolling resistance times the normal force.
F = Crr * N
The normal force for a stationary plane on the ground is the mass of the plane times the acceleration due to gravity. The drag force due to rolling friction is essentially a constant* and is independent of speed. Running the treadmill faster won't increase the drag force on the airplane--it'll just spin the tires faster.**
*Obviously, any lift generated by the plane would reduce the normal force and, hence, the rolling friction. Burning off fuel will reduce the weight of the plane and would also reduce the rolling friction.
**At high enough speeds the bearings in the wheels will heat up and eventually melt. I guess that would increase the coefficient of rotational resistance and, ultimately, the drag force.
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20 Dec 2006, 23:13
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#94
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so f*cking zen
Join Date: Jan 2003
Location: Hitting Bottom
Posts: 8,499
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Re: A Plane Problem
OK i'll attempt to break this up into bits. To begin with:
1.) "In this example do you think that the plane needs to be moving forward (never mind how it does it) in order to achieve lift?"
I believe that it does.
2.) "Do you believe lift would be generated if the plane remained stationary but its engines were on?"
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20 Dec 2006, 23:14
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#95
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Bad Girl
Join Date: Sep 2000
Location: right here..right now
Posts: 1,055
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Re: A Plane Problem
higher airflow under the wing than on top creates lift .. it wont take off.... there is no airflow...as the plane is on a tread mill .. not running on a flat surface .. creating air flow...
(the non technical explantion i didnt read the earlier posts)
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20 Dec 2006, 23:17
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#96
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The Twilight of the Gods
Join Date: Jan 2001
Posts: 23,481
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Re: A Plane Problem
Quote:
Originally Posted by Mistwraith
higher airflow under the wing than on top creates lift .. it wont take off.... there is no airflow...as the plane is on a tread mill .. not running on a flat surface .. creating air flow...
(the non technical explantion i didnt read the earlier posts)
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You didn't read the earlier posts proving you're wrong?
Quote:
Originally Posted by Dace
OK i'll attempt to break this up into bits.
2.) "Do you believe lift would be generated if the plane remained stationary but its engines were on?"
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No. Whatever you say next had better be really, really good.
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20 Dec 2006, 23:34
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#97
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Registered User
Join Date: Feb 2006
Posts: 1,094
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Re: A Plane Problem
I don't understand the question, the treadmill always matches the speed of the plane in what sense? Anyway i googled and found this which seems a good explanation.
If you stood on a treadmill and someone pulled you with a rope, they'd be able to pull you off the treadmill, similarly if you were on an icy pond you may not be able to 'pull' yourself off the pond because you kept slipping, but someone throwing you a rope would be able to pull you off the pond.
The force being used is 'external' to where the 'frictionless' environment is. The engines on a plane are the rope, they don't 'use' friction with the ground.
On a long enough treadmill the plane would be able to takeoff, just as a plane is able to takeoff from antarctic/artic environments that have 'ice runways' which is what i think the question may be alluding to with the 'treadmill matching the speed of the plane' bit, ie frictionless environment.
Quote:
Originally Posted by dda
There is a reason why airports have runways facing in different directions and swithch the airplanes around so that, as far as practical, airplanes take off and land heading into the wind.
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They haven't built major airports in that manner for half a century!! Runways are now routinely built parallel to each other, like the two existing ones and planned third at heathrow. Jet airliners offset their landing gear when landing in cross winds
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20 Dec 2006, 23:47
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#98
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Registered User
Join Date: Feb 2006
Posts: 1,094
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Re: A Plane Problem
Quote:
Originally Posted by Dace
2.) "Do you believe lift would be generated if the plane remained stationary but its engines were on?"
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No i dont, but the plane on the treadmill wouldn't remain stationary.
Imagine if it were a glider on the treadmill, with a rope attached to another plane that flew alongside, would the plane that was flying be able to pull the glider off the treadmill?
The thrust of the plane that was doing the pulling wasn't dependant on friction with the ground, and it would be able to pull the glider off the treadmill.
All a treadmilll would do is make the wheels of the plane spin round a lot faster.
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21 Dec 2006, 00:12
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#99
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:alpha:
Join Date: May 2002
Location: London, UK
Posts: 7,871
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Re: A Plane Problem
Did Dace die halfway through writing his post?
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21 Dec 2006, 01:10
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#100
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USS Oklahoma
Join Date: Jun 2005
Posts: 2,500
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Re: A Plane Problem
Does the plane need to move in order to move? Seems very likely.
A plane at rest tends to stay at rest unless acted on by an outside force.
It is clearly movement through the air that causes a plane to lift. The flaw seems to be that the treadmill, no matter how quickly it moved would be able to do anything except make the wheels move faster not impede the forward movement of the plane.
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