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Old 08-18-2006, 09:54 PM
  #241  
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(a)If it is spinning as theoretically fast as would happen they would melt and the thing would lose its ability to move at all. If a car wheel bearing siezes on the highway it locks up rather than being forced to turn. the airliner would drag the tires until they burst, then drag the metal. A normal airliner cant take off on the metal that supports the landing gear, there is not enough thrust to drag it to a suitable takeoff speed.

(b)My grandfather flew prop planes, single engine

Mike
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Old 08-18-2006, 09:55 PM
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Originally Posted by crazymjb
(a)If it is spinning as theoretically fast as would happent hey would melt and the thing would lose its ability to move at all. the airliner would drag the tires until they burst, then drag the metal. A normal airliner cant take off on the metal that supports the landing gear, there is not enough thrust to drag it to a suitable takeoff speed.

(b)My grandfather flew prop planes, single engine

(a) I think that's taking this problem a little too far.

(b) got it. you must be an expert then.
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Old 08-18-2006, 09:57 PM
  #243  
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No... But nowhere does it say this is an airliner... So if its a prop plane... Im definatly right.

And no answer will be deamed correct until the mythbusters try it

Mike
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Old 08-18-2006, 10:00 PM
  #244  
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Originally Posted by crazymjb
No... But nowhere does it say this is an airliner... So if its a prop plane... Im definatly right.

And no answer will be deamed correct until the mythbusters try it

Mike

Actually, you're still wrong. And I think you're missing the point of the problem. For example, if you really wanted to be right, you could have just assumed this was the Wright Brother's plane.

But that's ok. You're try was cute and you made a good effort.
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Old 08-18-2006, 10:01 PM
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Originally Posted by wstevens
Actually, you're still wrong. And I think you're missing the point of the problem. For example, if you really wanted to be right, you could have just assumed this was the Wright Brother's plane.

But that's ok. You're try was cute and you made a good effort.


Just hope that when you finally do take a physics course, this isn't the only problem on the final exam.
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Old 08-18-2006, 10:01 PM
  #246  
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mjb, for any mechanical device there is a theoretical breaking point, that doesn't mean it won't work under normal conditions (like in this question). You wouldn't say a combustion engine can't work at all because at a million rpm the pistons would melt. Just because the bearings would melt for this plane if the treadmill was going 20,000 mph, doesn't mean that this wouldn't work at a realistically obtainable speed.



by your logic I don't think there is any technology that would work, since there is always an extreme you could suggest at which it would explode
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Old 08-18-2006, 10:02 PM
  #247  
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I still don't see the problem with my reasoning...

My try was grand... Your try was cute

Mike
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Old 08-18-2006, 10:03 PM
  #248  
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Originally Posted by BEETROOT
mjb, for any mechanical device there is a theoretical breaking point, that doesn't mean it won't work under normal conditions (like in this question). You wouldn't say a combustion engine can't work at all because at a million rpm the pistons would melt. Just because the bearings would melt for this plane if the treadmill was going 20,000 mph, doesn't mean that this wouldn't work at a realistically obtainable speed.
Meh. I'm still waiting for the source of his bearing friction equation.
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Old 08-18-2006, 10:06 PM
  #249  
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Originally Posted by wstevens
Meh. I'm still waiting for the source of his bearing friction equation.

everyone knows bearing friction = 0.0000000001 * 10-x
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Old 08-18-2006, 10:10 PM
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An ICE would theoretically work at that speed of cooled properly... but they aren't built like that. The valve springs would lose there ability to keep up as well as the thing could in no way ever be balanced well enough to turn at 1 million RPM...

Anyway. A "Stock" plane on a giant treadmill... I still think I'm right. I am not saying it is beyond possibility that you guys are... But I have an "engineering" background, it's natural to me, one of the few things...

Yes, I know has a degree.... But I will someday too

Mike

Last edited by crazymjb; 08-18-2006 at 10:12 PM.
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Old 08-18-2006, 10:11 PM
  #251  
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Originally Posted by crazymjb
But I have an "engineering" background, it's natural to me, one of the few things...

Mike

Funny. So do I.
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Old 08-18-2006, 10:13 PM
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Yeah... I added the edit.

As an engineer wouldn't you like to see your point "tested"?

Mike
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Old 08-18-2006, 10:14 PM
  #253  
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Old 08-18-2006, 10:18 PM
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Originally Posted by crazymjb
Yeah... I added the edit.

As an engineer wouldn't you like to see your point "tested"?

Mike

You mean "tested" as in someone arguing with me or "tested" as in actually physically testing this treadmill concept?

If the former, sure I'm all for arguing. There's very little room for arguement in this one, unless you disagree with Newton and/or can't draw a simple free body diagram.

If the latter, then also yes. A giant treadmill would be kick-ass.
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Old 08-18-2006, 10:21 PM
  #255  
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Haha... Arguing is fun... But this comes down to a case that at the least varies plane to plane...

For example, you admit that if it was the wright flyer it wouldnt work, or another very small plane with low thrust still manufactured today?

Mike
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Old 08-18-2006, 10:50 PM
  #256  
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Originally Posted by crazymjb
Haha... Arguing is fun... But this comes down to a case that at the least varies plane to plane...

For example, you admit that if it was the wright flyer it wouldnt work, or another very small plane with low thrust still manufactured today?

Mike
The thrust needs to do 2 things in this situation. First, compensate for the friction of the wheels. Second, get the plane enough speed so that the air provides lift.

If it takes x units of thrust to achieve take off speed, I would guess it takes 1/100,000x to compensate for the extra friction from the wheels spinning faster, if any at all.

I will put $1 cold hard cash that there isn't a single plane manufactured post Wright brothers that has sufficient power for take off (x), yet can't manage to get that extra 1/100,000x to make up for the extra friction of the wheels spinning at 310 mph instead of 155.
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Old 08-18-2006, 10:53 PM
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Originally Posted by BEETROOT
The thrust needs to do 2 things in this situation. First, compensate for the friction of the wheels. Second, get the plane enough speed so that the air provides lift.

If it takes x units of thrust to achieve take off speed, I would guess it takes 1/100,000x to compensate for the extra friction from the wheels spinning faster, if any at all.

I will put $1 cold hard cash that there isn't a single plane manufactured post Wright brothers that has sufficient power for take off (x), yet can't manage to get that extra 1/100,000x to make up for the extra friction of the wheels spinning at 310 mph instead of 155.

....and I think we should just totally forget about the wheels melting. That's just a distraction to the problem. The problem is not meant to be taken that literally.
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Old 08-18-2006, 10:55 PM
  #258  
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Originally Posted by wstevens
....and I think we should just totally forget about the wheels melting. That's just a distraction to the problem. The problem is not meant to be taken that literally.

Yeah thats what I was saying earlier. With that logic my pen won't write because if I could move my hand a million miles per hour the ink would light on fire.
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Old 08-18-2006, 10:59 PM
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I think this has been pretty much put to bed.

I'm gong to go smoke some pot.
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Old 08-18-2006, 11:08 PM
  #260  
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back to chemistry homework for me. daltons atomic theory ftw
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Old 08-18-2006, 11:12 PM
  #261  
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I bought Guns Germs and Steel... Going to procrastinate at least a few more days though...

And again. I believe there would be much more additional resistance, enough to prevent take off....

Mike
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Old 08-18-2006, 11:16 PM
  #262  
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Originally Posted by crazymjb
I bought Guns Germs and Steel... Going to procrastinate at least a few more days though...

start that and let me know, I want to read it.

And again. I believe there would be much more additional resistance, enough to prevent take off....

Mike


Say a plane takes off at 155 mph (747 does). At this speed, the wheels spin freely and add a negligible amount of friction. You think somehow if the wheels rotational speed doubles there will be enough force to stop a jet engine!?

You are out of your mind. I'm outta here.
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Old 08-18-2006, 11:59 PM
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If it only doubled... But if the plane is actually moving one direction, and the treadmill starts up in the same speed the plane is moving in the oppoisite direction, it will never be able to match the wheel speed, making it go infinitly faster and hence making this situation impossible...

Mike
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Old 08-19-2006, 12:10 AM
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Originally Posted by crazymjb
If it only doubled... But if the plane is actually moving one direction, and the treadmill starts up in the same speed the plane is moving in the oppoisite direction, it will never be able to match the wheel speed, making it go infinitly faster and hence making this situation impossible...

Mike

Your statement, along with your points elsewhere in this thread, violate newton's third law and the first law of thermodynamics. How do you figure these two laws don't apply?

If you can't answer specifically, I suggest everyone in this thread add you to their ignore list.
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Old 08-19-2006, 12:32 AM
  #265  
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mjb, I get what you are saying now... and that 'straightdope' page has an response:

As you point out, one problem here is the wording of the question. Your version straightforwardly states that the conveyor moves backward at the same rate that the plane moves forward. If the plane's forward speed is 100 miles per hour, the conveyor rolls 100 MPH backward, and the wheels rotate at 200 MPH. Assuming you've got Indy-car-quality tires and wheel bearings, no problem. However, some versions put matters this way: "The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation." This language leads to a paradox: If the plane moves forward at 5 MPH, then its wheels will do likewise, and the treadmill will go 5 MPH backward. But if the treadmill is going 5 MPH backward, then the wheels are really turning 10 MPH forward. But if the wheels are going 10 MPH forward . . . Soon the foolish have persuaded themselves that the treadmill must operate at infinite speed. Nonsense. The question thus stated asks the impossible -- simply put, that A = A + 5 -- and so cannot be framed in this way.
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Old 08-19-2006, 12:37 AM
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Originally Posted by BEETROOT
mjb, I get what you are saying now... and that 'straightdope' page has an response:

Rotational speed and linear speed are two different things....I think that's where the misunderstanding comes in?
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Old 08-19-2006, 12:46 AM
  #267  
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exactly.
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Old 08-19-2006, 12:48 AM
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There also seems to be a misunderstanding of relative motion that the straightdope quote is trying to dispell.
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Old 08-19-2006, 12:49 AM
  #269  
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and to think... all my friends are out getting drunk and partying right now. those guys don't know what they are missing.
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Old 08-19-2006, 10:16 AM
  #270  
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Originally Posted by wstevens
Funny. So do I.

wstevens, get real If you are trying to stack your measley engineering degree and 10+ years of experience against his grade 10 engineering class, sorry but it just aint gonna fly.
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Old 08-19-2006, 10:59 AM
  #271  
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unbelievable... I think we are all wrong.

I sent this to a friend of mine who is an air force pilot:


No, if the pilot runs the engines up to full RPM the plane will start moving and the conveyor will be moving in the opposite direction right? So now the wheels are spinning twice as fast as the would be if it was accelerating on a normal runway. Airplane tires are rated to a certain speed before they explode which is not much higher than normal take off speed. Once the plane accelerates to near this speed the tires would explode sending rubber shrapnel into the engine intakes effectively FOD'ing them out (foreign object damage). The engines would light on fire and explode. The plane would not get airborne.
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Old 08-19-2006, 11:06 AM
  #272  
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Old 08-19-2006, 11:10 AM
  #273  
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OK you engineering minded people I have a question. In this instance, does it matter that the treadmill/conveyor is activley rotating in the opposite direction as the wheels? IE, it's not just some rollers, this thing is actively being driven to counteract any motion by the wheels?

I understand that the wheels/tires are entirely passive for thrust, it just seems that if the "ground" (aka conveyor belt) is moving in the opposite direction as the thrust is pusing the plane then the plane won't move - the wheels will spin really fast, but the plane ain't going anywhere.

I think part of the confusion for me is separating out a passive system (rollers just sitting there with zero friction) from a system that is actively counteracting the forward motion of the plane like the conveyor belt in this question.

Drinking wine last night didn't offer me any new insight - anyone else get buzzed and solve the meaning of life?
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Old 08-19-2006, 11:13 AM
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I agree if it linear speed then it would take off(maybe not on fighters though)... I thought it was matching the wheel speed though...

fdl... I'm not an idiot, I recognize he has higher credentials and does know more about this than me(generally), but If I see a point as valid(which since it appears to have been a misunderstanding, was), than why not defend it?

Mike
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Old 08-19-2006, 11:14 AM
  #275  
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Drinking wine last night didn't offer me any new insight - anyone else get buzzed and solve the meaning of life?
All the time.
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Old 08-19-2006, 11:21 AM
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That job is reserved for taking craps.

Mike
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Old 08-19-2006, 12:09 PM
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Originally Posted by fdl
wstevens, get real If you are trying to stack your measley engineering degree and 10+ years of experience against his grade 10 engineering class, sorry but it just aint gonna fly.

No pun intended?
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Old 08-19-2006, 12:10 PM
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Originally Posted by BEETROOT
unbelievable... I think we are all wrong.

I sent this to a friend of mine who is an air force pilot:

If we're assuming that a giant treadmill can exist, then I'm assuming the tires stay intact during this deal.

Last edited by wstevens; 08-19-2006 at 12:12 PM.
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Old 08-19-2006, 12:11 PM
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Originally Posted by crazymjb
I agree if it linear speed then it would take off(maybe not on fighters though)... I thought it was matching the wheel speed though...

fdl... I'm not an idiot, I recognize he has higher credentials and does know more about this than me(generally), but If I see a point as valid(which since it appears to have been a misunderstanding, was), than why not defend it?

Mike

You haven't answered my question about newton's law or the first law of thermo. What's your answer?

If you're going to defend your opinion, you look like an idiot (or a Water-S) if you only pick and choose which questions to answer.

Last edited by wstevens; 08-19-2006 at 12:14 PM.
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Old 08-19-2006, 12:36 PM
  #280  
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Originally Posted by wstevens
No pun intended?
pun intended
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