Riddle me this batman

[MA_PE]

So really what you're saying is that your mother and my mother are both mothers therefore we could be brothers, correct? :dunno:

 

[civengPE]

So really what you're saying is that your mother and my mother are both mothers therefore we could be brothers, correct? :dunno:

What would we be if we were both mothers also? :wacko:

 

[DVINNY]

still, the best thread ever.

still, the plane takes off just fine.

 

[IlPadrino]

I think his point is that if the wheels are allowed to move freely and the conveyor starts to move but no force is applied to the plane via the engines the wheels should turn, but the plane should remain stationary despite what the conveyor is doing. Newtons first law of motion, a body will stay at rest unless a force acts upon it. Since the wheels rotate freely, no force should be transfered to the body of the plane, the plane shouldn't move and the conveyor will just cause the wheels to role.

We've got to be careful to define "stationary". If the airplane moves at the same speed of what it's sitting on, this is not stationary, right? Let's call this "staying still on the moving surface".

I almost agree with what you wrote above... except the airplane won't remain stationary (it will stay still on the moving surface) as the moving surface first begins to move because there is rolling resistance in the wheels. At some velocity, though, the relative wind pressure will provide sufficient force to counter the rolling resistance and the airplane will stop moving at the same speed as the moving surface.

How can we rewrite Fact 3 to me more clear? Maybe:

Fact 3: Given an airplane sitting freely on any movable surface (e.g. a conveyor belt, a trailer, etc.), a force equal but opposite to the rolling resistance (i.e. rolling friction) of the airplane wheels will keep the airplane stationary despite the moving surface.

 

[benbo]

Wait a second. Where does Monty Hall fit into all this? Now there's a problem on which you will never get agreement.

 

[civengPE]

Wait a second. Where does Monty Hall fit into all this? Now there's a problem on which you will never get agreement.

Sorry about that. i did a quick cut/paste. it had to do with some earlier comments the OP had made.

 

[benbo]

Sorry about that. i did a quick cut/paste. it had to do with some earlier comments the OP had made.

There's nothing wrong with what you posted. My comment was supposed to be an unrelated joke. As it turns out, it was unrelated but not much of a joke. It refers to another old riddle that had a rather lengthy argument thread. Lucky I have my day job for now.

 

[Guest]

^^^ Wait a min ... I thought we all agreed (even I rescinded previous statements) that it was better to SWITCH than stay.

Right?

JR

 

[Dleg]

Good God.

 

[rdbse]

Ha! Is the model airplane on a treadmill the basis for the problem statement?

We can see it does not take off from the treadmill, but it only moves forward with no flight.

Can someone post the original riddle, so we can clarify the infinite conveyor.

 

[civengPE]

Ha! Is the model airplane on a treadmill the basis for the problem statement?
We can see it does not take off from the treadmill, but it only moves forward with no flight.

Can someone post the original riddle, so we can clarify the infinite conveyor.

:brickwall: :brickwall: :brickwall: :brickwall:

 

[rdbse]

Well, did it take flight? I have agreed all along it would move forward.

Now, let's seperate theory from reality.

 

[benbo]

Well, did it take flight? I have agreed all along it would move forward.
Now, let's seperate theory from reality.

Yes. It took flight. Satisfied?

The infinite conveyor is not in the original problem statement (which is in the in the thread). There was no length given, so I assumed it was a long conveyor, you assumed it was a very short conveyor. I already agreed that if the conveyor is short like you think then you are right - no plane could take off. But, given a long enough conveyor, any plane would take off.

Agreed? I mean, you already agreed it moved forward, so if it moves forward far enough it will take off.

Then we have no difference of opinion.

I don't know what your issue is.

 

[rdbse]

What video did you watch? The model plane was supported on a string.

I just want a clarification on the original problem, or maybe I should just wait on the MB episode.

You better just hold the controls straight and steady.

http://meignorant.com/2posts/Fly-NotFly.gif

 

[benbo]

What video did you watch? The model plane was supported on a string.
I just want a clarification on the original problem, or maybe I should just wait on the MB episode.

You better just hold the controls straight and steady.

http://meignorant.com/2posts/Fly-NotFly.gif

I don't know what you're talking about with a video. Where do I say I watched a video? Or are you talking to someboy else. I actually put a model plane with a rubber band prop on an exercise treadmill and guess what, it took off. And it was going a hell of a lot slower than the treadmill.

Here's the original question. It is from the first post in this thread. As I said, I assumed that the conveyor was very very long. You still refuse to answer the question, if the conveyor is infinitely long, or lets say ten miles long - will the plane take off? Is that hard to answer? By the way, hundreds of other people don't seem to have a problem. I'm done beating this horse.

The question is:

A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction).

Does the plane ever take off, and why or why not?

 

[DVINNY]

Sapper, so you're saying it will fly?

LMAO

 

[rdbse]

Hey Sapper,

I did not force you to look at this thread again, so no reason to get ill. You contradict yourself by saying it does not matter how short the conveyor is, but add that it needs to be long enough to obtain critical velocity. If we can agree that the length does matter, I will agree that the plane will fly and let it rest.

 

[MA_PE]

^^^ Wait a min ... I thought we all agreed (even I rescinded previous statements) that it was better to SWITCH than stay.
Right?

JR

Despite the lengthy statistical arguments (which are likely valid) I still believe it's a 50/50 chance. :smileyballs:

 

[IlPadrino]

Hey Sapper,I did not force you to look at this thread again, so no reason to get ill. You contradict yourself by saying it does not matter how short the conveyor is, but add that it needs to be long enough to obtain critical velocity. If we can agree that the length does matter, I will agree that the plane will fly and let it rest.

You're not following the rules - only one new fact at a time.

I left off with



Fact 1: Any flying (not falling!) airplane requires sufficient air velocity over its wings to generate enough upward lift which counteracts the airplanes mass (which given gravity creates a downward force).

Fact 2: An airplane creates thrust independent of its wheels.

I think I need to change Fact 3 to include axle friction because it'll come to play in the next Fact. So:

Fact 3: Given an airplane sitting freely on any movable surface (e.g. a conveyor belt, a trailer, etc.), a force equal but opposite to the rolling resistance (i.e. rolling friction) and axle friction of the airplane wheels will keep the airplane stationary despite the moving surface.

then we can go to

Fact 4: Rolling resistance is a function of [what?] and axle friction is a function of [what]?

I don't know... a quick Google makes me think I just need to ask the Pine Car Derby enthusiasts.

I think we'll quickly get to the end after this... because no matter how fast the conveyor moves (which causes the wheels to spin even fast that they would if the conveyor wasn't moving), the extra rolling resistance and axle friction is quite small compared to the thrust of the airplane.

Sapper: I only go through this "debate" because I think there's still something to be learned (other than who was right or wrong). I thought it strange there wasn't a lot of discussion about rolling resistance and axle friction.

 

[BluSkyy]

To me, its a relatively simple dynamics problem. The sum of the forces acting on the plane is nonzero, therefore there is an acceleration. I don't see why its so hard.