think about this...

[LAGmaniac]

[ QUOTE ]
The only way Pat can own me here is if he uses a different interpretation of "The runway moves in the opposite direction of the plane at the exact same speed as the plane's wheels" than the one I am using. I consider conveyor belt movement to be ft/sec over its pulley, and wheel movement to be ft/sec over its rolling surface.

[/ QUOTE ]

Exactly, that's the only definition that makes sense in this problem.

[ddubois]

I get the impression that Pat is considering belt movement to be "wheel surface travelled" and wheel movment to be "belt surface travelled", which, frankly, is a big LOL.

[NLSoldier]

[ QUOTE ]
if its a normal plane, it doesnt move and hence doesnt take off


[/ QUOTE ]

Wrong.

[ QUOTE ]
I get the impression that Pat is considering belt movement to be "wheel surface travelled" and wheel movment to be "belt surface travelled", which, frankly, is a big LOL.

[/ QUOTE ]

If Pat is as poor at metric conversions as he is at reading comprehension, I hear NASA has an opening for him.

[NutCrackerr]

(puff)............................... (exhale)

If it were possible for a plane to take off from a conveyor type runway, how come one doesn't exist?

[MrWookie47]

OK, let's put the plane at the end of the runway at rest, just like it normally is. However, we're on a magic runway that can move at whatever speed necessary to meet the condition of OP. So the runway moves at the same speed as the wheels. What part of the wheels? Well, the obvious point is the contact point of the wheels, but I say to hell with that. Let's say the whole [censored] wheel can't have any velocity relative to the runway. So, we fire up the engines. The enines propel air backwards and the plane forwards. But, holy [censored]! That means the wheels are moving! We gotta get that runway going! So the runway accelerates too, and the wheels remain motionless. Mean while, the plane is still accelerating. Holy [censored]! We can't have the wheels moving! Heap some more magic dust into the runway motor so it speeds up! And the wheels don't move. And now the plane speeds up again. Holy [censored]! But this time, the plane has reached 88 miles an hour (relative to the air traffic control tower) and goes back in time. Wait til [censored] OOT hears about this!

[goofball]

[ QUOTE ]
(puff)............................... (exhale)

If it were possible for a plane to take off from a conveyor type runway, how come one doesn't exist?

[/ QUOTE ]

The plane would still have to move relative to the ground on said runway. It would be difficult to create and wouldn actually make it harder since more energy would be required to take off it than a stationary runway, since real airplane wheels have friction.

[4_2_it]

[ QUOTE ]
(puff)............................... (exhale)

If it were possible for a plane to take off from a conveyor type runway, how come one doesn't exist?

[/ QUOTE ]

Possible and practical are two different things. Plus no one has argued (yet) that you could land the plane on the conveyor belt.

[Josh W]

[ QUOTE ]
[ QUOTE ]
I'm sad.

I saw this thread a few hours ago, and thought it would be a 10 reply thread, then die in obscurity. I'm saddened greatly that there can be any sort of debate about this.

It's WINDSPEED that enables lift. If the plane isn't moving relative to the wind, it ain't going up.

As a very correlate aside, planes take off into the wind. They also land into the wind.

So saddened.

Josh

[/ QUOTE ]

I thought it was that simple when I first looked at it but it really is not. Nobody in this thread disputes that you need air flowing over the wings (forward movement) to create lift, (thank god).

The issues are whether the forward movement of the plane is prohibited by the conveyor belt, the original conditions of the problem, or neither.

[/ QUOTE ]

Doesn't:

[ QUOTE ]

The runway moves in the opposite direction of the plane at the exact same speed as the plane's wheels.


[/ QUOTE ]
mean no net movement? Same speed, opposite direction.

Bah, nm. I guess I could read the thread if I wanted to see what was causing the confusion.

So sad [img]/images/graemlins/frown.gif[/img]

I'm no physics expert, but I think I have an example that might satisfy Nasty/Crazy/goofball.

Imagine that there is no friction at all involved with the wheels and the conveyor belt. The wheels and the belt are moving at the same rate, but this is not necessarily because of friction.

Imagine that the conveyor belt and the wheels are both completely stationary. You expect the wheels to spin faster as the plane moves forward because of the effects of FRICTION BETWEEN the wheels and the conveyor belt. If there is no friction, then the wheels will remain stationary - regardless of the speed of the plane (and, incidentally, of the conveyor belt).

This is a specific hypothetical situation in which the plane clearly accelerates under the conditions outlined in the OP (there is no suggestion that the identical speeds of the wheels/belt are due to friction).

I'm not 100% sure how this situation works if the speed of the runway and wheels scale linearly due to friction, but I don't think it's relevant. Even if we imagine the speed of the wheels and the speed of the conveyor belt to be completely independent (they just happen to be identical), the principle of the solution stands.