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Old March 14th, 2007, 09:57 AM   #136
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I just found this thread for the first time, read through every reply and I have to go ahead and say ... that I really have no idea what the plane will do.
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Old March 16th, 2007, 09:43 PM   #137
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I'm kind of lost why this hasn't come to a consensus. We were just talking about a problem similar to this in my PHYS261 class. It was a slightly different setup but same properties. The plane will never move off the conveyor belt and thus never generate enough lift via wind velocity (see Bernoulli's principle) to get off the ground. Regardless of the propulsion provided by the engines, the plane cannot leave the conveyor belt if it matches its velocity.

The comparison made previously with ice is not similar in any way. Ice is simply a frictionless surface; this conveyor belt actively negates any horizontal force exerted on the craft to move it.
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Old March 16th, 2007, 10:08 PM   #138
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Yay, Ben... That was my argument back in the early posts. Took a lot of heat from most....
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Old March 16th, 2007, 10:52 PM   #139
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I can't believe I'm going to reply again but what heck, it's a slow Friday night. Ben, the plane will take off. Here's the Straight Dope:

http://www.straightdope.com/columns/060203.html

Last edited by Tim Le; March 17th, 2007 at 12:52 PM. Reason: Unnecessary physics gibberish
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Old March 17th, 2007, 05:50 AM   #140
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Quote:
Originally Posted by Ben Winter View Post
I'm kind of lost why this hasn't come to a consensus. We were just talking about a problem similar to this in my PHYS261 class. It was a slightly different setup but same properties. The plane will never move off the conveyor belt and thus never generate enough lift via wind velocity (see Bernoulli's principle) to get off the ground. Regardless of the propulsion provided by the engines, the plane cannot leave the conveyor belt if it matches its velocity.

The comparison made previously with ice is not similar in any way. Ice is simply a frictionless surface; this conveyor belt actively negates any horizontal force exerted on the craft to move it.
THE PLANE HAS WHEELS!!!!!!!!!!!
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Old March 17th, 2007, 06:04 AM   #141
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Quote:
Originally Posted by Ben Winter View Post
...We were just talking about a problem similar to this in my PHYS261 class...
Ben, please send me your physics instructor's email so I can advise him/her to fail you!
;-)

I'm going to resist the almost overwhelming urge to lock this thread. Instead, I think I'll just mercilessly taunt anyone who re-posts any arguments or facts, correct or faulty, that have already been stated earlier in this ridiculously long thread. And then I shall taunt you a second time.
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Old March 17th, 2007, 07:35 AM   #142
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Ben, the mistake you are making is the assumption that the plane will be stationary because the belt matches its speed. I made this mistake too, as you will see if you read the thread. In a realistic scenario there is not enough friction between the plane and belt for this to happen, therefore the plane will eventually move ahead and fly regardless of what speed the belt is running at.
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Old March 17th, 2007, 10:58 AM   #143
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Pete

For the LOVE OF GOD.... FOR WHATEVEVER you hold dear...

PLEASE PLEASE PLEASE LOCK THIS THREAD!!!!

You're killing me man!!!!!!!!!!!!!!!!
(Post #11... THE CORRECT ANSWER)
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Old March 17th, 2007, 11:24 AM   #144
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Don't forget that excellent post #21.

It may be somewhat frustrating, I agree, but no real reason to close it. If it were just about how irritating a post can be, there would be dozens of them closed, starting with most of the ones that ask, "What Tape Do You Use In Your---------," and Should I Use A Cleaning Tape, and What Kind?"

Mike :)
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Old March 17th, 2007, 10:55 PM   #145
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Hey Ben. We jeanusus has to stik two gather !!
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Old March 19th, 2007, 10:33 AM   #146
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Quote:
Originally Posted by Gene Crucean View Post
Here is a question that will for sure get you guys thinking.

If you have a large jet plane (747) sitting on a runway that was actually a giant conveyor belt (go with it). And there is also a device on the plane that communicates with the conveyor belt to tell it how fast the plane is traveling, which would then make the conveyor belt match the speed IN REVERSE.

Can the jet take off?
Hmmm...

interesting. "speed" in the proposed situation needs to be clarified...ground speed or air speed?

In this problem, if it was ground speed that the conveyor belt would match, there is an issue with theoretical reponse time...

If the conveyor responded instantly (since we're theoretical, we can do that), and it was groundspeed, from the wheels, the jet engines would move the airplane itself forward regardless of the conveyor belt's acceleration as the airplane moves itself through the air...the wheels would be turning infinitley fast as they would continue to accelerate as the belt would accelerate to compensate for the fact the wheels are attached to the plane, which would move forward based on the engines pushing the body, without direct relationship to the wheels rotation speed and inverse motion of the conveyor ...negating kinetic friction of the rubber and the conveyor surface and any operating range of bearings and bushings and flash point of any flammable lubricants contained therein...which would most likely simply incinerate the wheels during the whole procedure...provided the conveyor didn't simply fly apart.

If the conveyor responded to airspeed...largely the same scenario would apply, with the exception of the acceleration curve probably wouldn't be as steep as the groundspeed scenario because the response of the conveyor would be directly inverse to the forward motion of the aircraft (without the acceleration influence of the conveyor's compensatory movement on the wheel acceleration, which creates wheel speed as a rapidly increasing multiple of actual forward motion due to the wheels direct contact with the conveyor), though the acceleration would still be a bit of a logarithmic curve as the belt will have to accelerate, but would max out at the exact inverse of lift off speed.

In the airspeed compensation scenario, the wheels would rotate at a theoretical maximum of 2X liftoff speed (1X for the aircraft forward motion, another 1X to compensate for the inverse belt movement), whereas the groundspeed scenario could create an almost infinite amount of wheel acceleration.

If the wheels didn't burn up and the conveyor belt held together, in either case the airplane would move based on the engines pushing the fuselage, not the relative speed of the wheels, therefore it WOULD move and would takeoff.

:-) Whew!
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Old March 23rd, 2007, 11:26 PM   #147
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Ah...yes in the scenario we discussed in class, the conveyor belt (or in our class' example a wheel) was motorized to match the velocity of the airplane.

Actually, our problem dealt with a model plane and a weight, and did involve friction, although it was not stressed as the reason for taking off...I'll take a peek at it again. Perhaps not so parallel a problem after all. Although it still seems to me that if the conveyor belt is actively...no wait, I guess it's frictionless. Sigh.

*steps back* you should probably lock this now.
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Old March 31st, 2007, 11:38 AM   #148
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My Mom is a Mensa member, I am not. I have not read any other responses so here's my input (or lack thereof)...
If I understand it correctly, the plane isn't moving forward, it's staying stationary while this giant belt rolls under the wheels....
No, the plane would have no lift so it could not take off... unless it had thrust similar to a Harrier jet's vertical takeoff, lol...
As long as the pilot doesn't "hit the brakes." (edit)
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Old March 31st, 2007, 06:16 PM   #149
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Ok Dave, I warned earlier that I'd taunt anyone who re-posted info that was already in the thread! Taunt: Of course you're not in Mensa; how could you pass the test if you don't READ!

I may taunt you a second time later, but there's hockey game on the Idiot Box (InHD) at present.
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Old April 1st, 2007, 11:24 AM   #150
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The plane flys.
Weight any 3 cubes against any 3 cubes,then any 2 from the heavy set.
1hour 30minutes.
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