Physics
Postmaster
Joined: Aug 2004
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From: North of Boston MA
Originally Posted by sigma
A plane (747 passenger jet) is sitting on a runway that can move (some sort of band conveyor). The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the planes speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).
Will the plane (747 passenger jet) take off or not?
Will the plane (747 passenger jet) take off or not?
Postmaster
Joined: Aug 2004
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From: North of Boston MA
Originally Posted by jgc2521
wouldnt overall speed be 0mph then.. compared to the ground
Hotshot
Joined: Apr 2004
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From: NW burbs of chicago
Originally Posted by DonsFx4
Sigma...congrats on posting a great topic! Got a lot of people thinking here.
Too bad it didn't include a poll to show how many think it will or will not fly!
Which, by the way, it WILL!!!
Too bad it didn't include a poll to show how many think it will or will not fly!
Which, by the way, it WILL!!!
Elder User
Joined: Jan 2004
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From: Marple Township, PA
Nitramjr...you got it right. 78f-150Super, sometimes I just can't come up with the right words to get my point across, so bear with me here:
The physical forces involved:
Thrust of engines - the high velocity jet blast out the engines will have a reactionary force, which is to move the plane forward
Forward velocity - as forward velocity increases, so does the speed of the air moving over the wings. The faster the speed, the more lift produced
Airplane wheels - The wheels are free-spinning, except of course when brakes are applied. As long as they are spinning, they act like roller bearings and completely nullify the effect of the runway
Runway - moving or stationary, it makes no difference to the plane as long as the engines are producing thrust, the plane is propelled forward by the reaction to that thrust, and the forward velocity relative to the AIR (not the runway) is enough to creat lift.
Whew...now it's time for a shot and a beer!
The physical forces involved:
Thrust of engines - the high velocity jet blast out the engines will have a reactionary force, which is to move the plane forward
Forward velocity - as forward velocity increases, so does the speed of the air moving over the wings. The faster the speed, the more lift produced
Airplane wheels - The wheels are free-spinning, except of course when brakes are applied. As long as they are spinning, they act like roller bearings and completely nullify the effect of the runway
Runway - moving or stationary, it makes no difference to the plane as long as the engines are producing thrust, the plane is propelled forward by the reaction to that thrust, and the forward velocity relative to the AIR (not the runway) is enough to creat lift.
Whew...now it's time for a shot and a beer!
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Elder User
Joined: Nov 2005
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From: San Antonio, TX
I was taking into account too many factors. I am leaning towards your answer right now DonsFx4. Still need to ponder.
EDIT: Yeah, Dons, you're probably right. I was going overboard with friction when the wheels could simply be free moving :-P In that case, there is negligible force between the plane and the ground and the engines can push the plane forward using the air as the medium.<o></o>
EDIT: Yeah, Dons, you're probably right. I was going overboard with friction when the wheels could simply be free moving :-P In that case, there is negligible force between the plane and the ground and the engines can push the plane forward using the air as the medium.<o></o>
Last edited by 78f-150Supercab; Dec 8, 2005 at 07:31 PM.
Posting Guru
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From: West Chester PA
Originally Posted by sigma
This conveyor has a control system that tracks the planes speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).
Elder User
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From: San Antonio, TX
But that only applies if the force of the plane is solely on the ground (the belt). But as Dons noted, the wheels act like bearings, negating any force that the belt has on the plane and it is the thrust that moves the plane forward.
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From: North of Boston MA
Originally Posted by maa139
Don't forget about this statement in the original problem. This statement means that the speed of the plane relative to the ground is 0.
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From: West Chester PA
Originally Posted by 78f-150Supercab
But that only applies if the force of the plane is solely on the ground (the belt). But as Dons noted, the wheels act like bearings, negating any force that the belt has on the plane and it is the thrust that moves the plane forward.
Elder User
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From: San Antonio, TX
Originally Posted by Nitramjr
No, the speed of the conveyor will only match the speed of the rotating wheels, in the opposite direction.