Plane on a conveyor belt
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tjamz;199249 wrote:
Please explain to me the physics involved that would be required for a conveyor belt to hold a plane stationary. It is IMPOSSIBLE.alright. for shits and giggles. the plane starts out, sitting still.
conveyor belt attempts to match the WHEEL speed. ends up going really damn fast. melts down the wheel bearings, because they aren't frictionless. wheels lock up. plane slows down. conveyor belt keeps trying to match the plane's speed without wheels.. and eats the plane away like a belt sander, causing the bits and pieces left to stand still.
ghetto physics. that's one tough conveyor belt.
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harm;199246 wrote:
on a FWD car the wheels are going to go the same speed as the conveyor belt, and the car is going to sit still. the rear wheels aren't driven wheels, so they go the speed of the car minus the speed of the road, and the car sits still.Forget about cars...that was a bad analogy by Faber.
just like the plane is going to sit still and not take off, the way the question is worded.
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Nope, it says it matches the speed of the moving plane. Not the momentum/force. Only the speed. It doesn't say the plane is stopped from moving forward. **If every bit of forward momentum gained is ripped away by a conveyor belt, the plane doesn't gather enough inertia to move, and if the plane doesn't move, it doesn't fly.
It does move, the question clearly states that
we're talking "real" plane and "imaginary" conveyor belt, though.. real-world, we don't have a belt that can take this on.
**
Mythbusters did, and the plane flies (real world) episode is on January 30th.**anything that gets set up to "test" in a real-world setting.. it'll probably fly. because the belt isn't going to be matching the plane's speed, just trying to catch up to the wheels.
**Again, it was done w/ a 1/4 mile long piece of conveyor belt being pulled by a pickup at the same speed as the airplanes take off speed (ultralight plane, so takeoff speed wasn't too high). Both started moving at the same time and the plane achieved take off speeds and lifted off. How do I know this? Well, I watched the teaser clip from here:
(listen to what the pilot has to say) http://dsc.discovery.com/fansites/mythbusters/mythbusters.html
then read the article here (read what they have to say about the pilot)
Think about this many many many people have changed their minds and said the plane will fly, no one (on any forum I've been on....and I've been on LOTS of them arguing this point) has ever (to my knowledge) switched to thinking it won't take off.
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harm;199251 wrote:
alright. for shits and giggles. the plane starts out, sitting still.conveyor belt attempts to match the WHEEL speed. ends up going really damn fast. melts down the wheel bearings, because they aren't frictionless. wheels lock up. plane slows down. conveyor belt keeps trying to match the plane's speed without wheels.. and eats the plane away like a belt sander, causing the bits and pieces left to stand still.
ghetto physics. that's one tough conveyor belt.
LOL, if you get infinite speed treadmill, I get indestructible wheel bearings and tires. :icon_cheers:
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JN210;199253 wrote:
OR!!!, the plane can speed up to speed (about 200mph) and then the conveyor belt can just stop.....that should get the plane somewhere:icon_cheers:Wouldn't affect the plane at any more than if it kept on spinning.
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I love this topic.
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a real aircraft on a conveyer belt moving backwards with its engines off will be pushed backwards, off the belt, because the tires and wheel hubs are not frictionless
turning on the engines will cause the plane to have a forward acceleration, but whether or not that counteracts the backwards motion of the belt depends on the specifics involved
if the belt is not powered via an external source, the plane definitely takes off
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JN210;199258 wrote:
if it just stopped (the belt) then the plane should rocket forward...thus making it go up?:icon_scratch: (assuming there is more runway)Nope, the plane doesn't care about the belt while its moving, so it won't care if it stops moving either.
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thrash;199257 wrote:
a real aircraft on a conveyer belt moving backwards with its engines off will be pushed backwards, off the belt, because the tires and wheel hubs are not frictionlessCorrect
turning on the engines will cause the plane to have a forward acceleration, but whether or not that counteracts the backwards motion of the belt depends on the specifics involved
Assuming the plane is capable of moving forward on a normal runway, it will be capable of it on this conveyor as well.
if the belt is not powered via an external source, the plane definitely takes off
Doesn't matter how its powered, plane takes off. The question could read "conveyor matches speed of plane at twice the normal rate" and the plane still takes off
I still love this thread.
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[quote]turning on the engines will cause the plane to have a forward acceleration, but whether or not that counteracts the backwards motion of the belt depends on the specifics involved
Assuming the plane is capable of moving forward on a normal runway, it will be capable of it on this conveyor as well.
[/quote]I am unconvinced. Why do you say that? Suppose that the plane develops only enough thrust to move it forward at 1mph (and never any faster, due to power and aerodynamic reasons not really seen on a real aircraft). Further suppose that the (powered) belt moves backwards with such violence that the plane, due to the friction in the wheels and tires, is going to be pushed back at somethingl like 200 mph. The plane certainly is not going to move forward in this situation.
[quote]
if the belt is not powered via an external source, the plane definitely takes offDoesn't matter how its powered, plane takes off. The question could read "conveyor matches speed of plane at twice the normal rate" and the plane still takes off
[/quote]I don't think so. See my point above -- if the belt develops so much reward motion on the plane such that the planes engines, at full thrust, are unable to make forward progress vs the belt, then by the same token, the plane is not making forward motion through the air, and thus, there's no lift, and no liftoff.
The reason i gave a cautious answer is because i can envision a system of engine output so low and wheel friction so high that the plane, at full throttle, on a powered belt, will either stay stationary or move backwards.
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thrash;199263 wrote:
I am unconvinced. Why do you say that? Suppose that the plane develops only enough thrust to move it forward at 1mph (and never any faster, due to power and aerodynamic reasons not really seen on a real aircraft). Further suppose that the (powered) belt moves backwards with such violence that the plane, due to the friction in the wheels and tires, is going to be pushed back at somethingl like 200 mph. The plane certainly is not going to move forward in this situation.I'm assuming no mechanical failures. I figured that was a given. So long as the plane is capable of getting the plane moving forward on the belt in the first place, it will continue moving it forward, completely unhindered by the belt (barring mechanical failure of bearings) Besides, the belt matches the planes forward speed. Once the static friction of the wheels is overcome, the plane will continue moving forward.
I don't think so. See my point above -- if the belt develops so much reward motion on the plane such that the planes engines, at full thrust, are unable to make forward progress vs the belt, then by the same token, the plane is not making forward motion through the air, and thus, there's no lift, and no liftoff.
This is impossible. Speed has very little to do with the friction of the bearings/wheels. Actually, the faster something spins, the less friction there is (until it becomes unbalanced and starts spinning erratically, causing wobbles and binding at the bearings resulting in overheating and malfunction)
The reason i gave a cautious answer is because i can envision a system of engine output so low and wheel friction so high that the plane, at full throttle, on a powered belt, will either stay stationary or move backwards.
Ok, IF you could have that much friction AND that little power to keep the plane motionless, sure, the plane won't take off. But then it wouldn't take off regularly either.
(tjamz is too lazy to use quote tags)
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tjamz;199249 wrote:
Posts like this make me want to cry.What part of the riddle makes you think the plane remains stationary?
Please explain to me the physics involved that would be required for a conveyor belt to hold a plane stationary. It is IMPOSSIBLE.
Ok, maybe you are referring to the alternate version of this riddle which states that the conveyor matches wheel speed in the opposite direction.....but wait, the only way to match the wheel speed would be for the conveyor and the plane to be traveling in the same direction (with the conveyor moving at 1/2 the speed of the plane which would mean the wheels would be spinning at 1/2 of their normal rate as well causing the conveyor and the wheels to be matched in speed) which certainly won't stop the plane from taking off either.
In your inline reply with his quote, I think that the word you are looking for is "regardless"
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I can't believe this topis is still being discussed. LOL
Maybe this will help... lets assume the jet engines are at full thrust, and the conveyor is moving like a mofo and you locked up the brakes on the plane. Would the plane come to a stop on the conveyor, or would the thrust of the engines keep pushing the plane forward just grinding the tires into a smoking pile? Of course it depends on the thrust of the engines, but I'd venture to guess that the majority of planes would continue accelerating even with the wheels locked up. The idea of the conveyor affecting the plane much at all with the brakes off is silly. Yes, there is a small amount of friction in the wheel bearings, but it's negligable.
Example 2: You have a baby stroller with a small jet engine in it, you get on the treadmill with the stroller and start pushing it. You stay in place in relationship to the ground as the treadmill matches your walking pace. You fire up the jet engine... what happens?
DaveH
'94 Supra- 7.77 @ 176mph -
if the conveyer belt is powered externally it is possible to concoct a scenario where the plane doesn't move forward enough, relative to the air, to take off.
Disagreeing with this is foolhardy -- it's the same argument as saying that you don't slow down when trying to swim against a current. A powered belt does counteract the forward motion of the plane, and to what extent depends on the belt and on the construction of the plane.
an externally powered, moving belt, DOES exert a force on the plane, and, in the absence of sufficient force vector opposite in direction, will cause the plane to move backwards. If the thrust of the engines is less than the force of the belt moving the plane backwards, the plane will move backwards.
Here's a fun experiment: a car (with tires), with its brakes off and in neutral is on a conveyer belt, rolling backwards. You are at the end of the belt, and behind you is a wall. Your job is to hold the car on the belt. You can use both arms if you want to.
Do you have to exert any effort to keep the car from crushing you? If so, how much?
I welcome anyone that thinks that it doesn't matter what the belt is doing to stand behind the car in my picture
You'll note that i didn't chime in on this thread until people started saying "no matter what, it takes off". I agree that in the problem, as stated, the plane takes off.
However, insofar as someone is willing to make an absolute statement that the plane takes off, irrespective of how the belt is moving or how it is powered, I think they are incorrect.
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Ok, the plane will NOT take off. A plane needs airlift to take off...and unless the air around the plane and the whole conveyor contraption is moving very fast (fast enough to lift a plane) it will not fly.....now if it was a rocket ship...that would be a different story due to it having rockets.
Info provided by my physics teacher:)
*1989 Nissan 300ZX Z31 *
> DelSlow;262050 wrote:
> I like the new JN210
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