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[FWNuke]

I never said any such thing, I've never disputed that there are times when a lateral force couldn be transmitted through a bearing.



At which point we're no longer discussing a plane with free-spinning wheels are we? If the wheels are glued to the treadmill they're not free to spin and are essentially locked to the axle, as such any force acting on them will be transmitted to the axle and the rest of the plane.

The wheel is free to spin still, it's just that it takes a lot more acceleration to do it because the friction between the tire and treadmill is so high.
If you start the treadmill slowly enough, you will move the plane with frictionless bearings.

 

[Son of Sluggish]

By the way, Congrats on the new PM!

A NATION ONCE AGAIN! A NATION ONCE AGAIN!!
(sing it with me)

 

[Scouse]

Gents. The only true proof is mathematical proof. Get to it!

 

[FWNuke]

Yeah but I wanna see if it is possible to educate a Yank. So far it'd appear not. They seem to live in a strange world where if you spin a wheel it doesn't spin, it instead tries to move the entire object it's connected to backwards.

You are the one that can't grasp this. I happen to have a pretty darn high IQ. I'm not stupid.

You may be beginning to see it though, because you seem to have stumbled over a couple of your own arguments.

You started out saying that a lateral force would not be transferred through a frictionless bearing.

You also said that mass makes a difference in the unicycle example. If you agree that a light unicycle would fall, then you have just agreed with me that a lateral force is transmitted through a frictionless bearing and you have lost the argument.

Seriously, take the question to a physics professor and they will tell you that I am right.

 

[Scouse]

You are the one that can't grasp this. I happen to have a pretty darn high IQ. I'm not stupid.

Just out of interest. What's a high IQ in the US of A then?

 

[Krazeh]

You started out saying that a lateral force would not be transferred through a frictionless bearing.

Again I never said anything of the sort, please tell me where I have ever said that under no circumstances could a lateral force be transferred through a frictionless bearing.

You also said that mass makes a difference in the unicycle example. If you agree that a light unicycle would fall, then you have just agreed with me that a lateral force is transmitted through a frictionless bearing and you have lost the argument.

You'll have to forgive me as it's fairly late here and my brain may be shutting down but my point about mass related to the inertia of the systems. Not that agreeing with you that a lateral force could be tranmitted through a frictionless bearing would lose me the argument as I have never stated that it couldn't be.

 

[FWNuke]

A car in a vacuum with frictionless bearings coasting on a flat surface will slow down and stop because of rolling friction between the road and the tire's surface.

The friction of the road/tires is applying lateral resistance to the vehicle's forward motion.

 

[FWNuke]

Okay, it's been fun having this discussion. Hope you have a great night.

 

[Son of Sluggish]

A car in a vacuum with frictionless bearings coasting on a flat surface will slow down and stop because of rolling friction between the road and the tire's surface.

The friction of the road/tires is applying lateral resistance to the vehicle's forward motion.

Yeah... But... The car's engine is connected to the wheels!

 

[Krazeh]

Why... You don't think that an airplane is physically attached to its wheel? If there is inertial force pulling back on the wheels, it is pulling back on the entire plane.

In fact... If you take a small plane like a Piper Cub... Next to the engine, the wheels probably hold the most mass of any component in whole plane. With its weak thrust to weight ratio, it wouldn't take a whole lot of rotational inertia to prevent it from moving forward. Of course, if the conveyor belt reached its maximum speed, rotational inertial would cease and the plane would move forward.

I don't expect any of you to understand this.

Just so i'm clear you're saying that you could eventually create enough momentum through the rotational inertia of the turning wheels to accelerate the plane backwards at the same speed that the engines are accelerating it forwards??

I think i'll stick with my view that the entire undercarriage would have spectacularly self destructed well before you could get the wheels spinning anywhere near fast enough for the backward force produced through their rotational inertia to come anywhere close to the forward force produced by the plane's engine(s).

Also what exactly would be stopping the plane from accelerating forwards and taking off anyway while the treadmill is spinning the tyres upto a speed where the rotational inertia could possibly begin to have any effect?

 

[Krazeh]

A car in a vacuum with frictionless bearings coasting on a flat surface will slow down and stop because of rolling friction between the road and the tire's surface.

The friction of the road/tires is applying lateral resistance to the vehicle's forward motion.

Yes it would slow down, the friction of the road on the tyres would cause them to slow their forward movement which would mean the inertia of the car would push the axles laterally against the wheel bearings. This would continue, slowly transferring energy from the body of the car to the wheels, which would then be lost most probably as heat due to friction between the road and the tyres.

 

[Son of Sluggish]

Just so i'm clear you're saying that you could eventually create enough momentum through the rotational inertia of the turning wheels to accelerate the plane backwards at the same speed that the engines are accelerating it forwards??

I think i'll stick with my view that the entire undercarriage would have spectacularly self destructed well before you could get the wheels spinning anywhere near fast enough for the backward force produced through their rotational inertia to come anywhere close to the forward force produced by the plane's engine(s).

Also what exactly would be stopping the plane from accelerating forwards and taking off anyway while the treadmill is spinning the tyres upto a speed where the rotational inertia could possibly begin to have any effect?

Once again, I'm talking about acceleration, not ultimate speed. Once the conveyor belt/ wheel's speed leveled off the plane would easily take off. Only the reverse acceleration of the conveyor belt/wheel would prevent the plane's forward motion.

I'm beginning to think you're not reading what I'm writing.

 

[Krazeh]

Once again, I'm talking about acceleration, not ultimate speed. Once the conveyor belt/ wheel's speed leveled off the plane would easily take off. Only the reverse acceleration of the conveyor belt/wheel would prevent the plane's forward motion.

I'm beginning to think you're not reading what I'm writing.

Where did i say anything in that post about ultimate speed? I was simply clarifying that you were of the view that you could have a situation where you had a treadmill that could create enough momentum through the rotational inertia of a plane's wheels to counteract the forward acceleration being produced by the thrust from the engines? And that I was of the view that the undercarriage would have self destructed long before the rotational inertia of the wheels reached any sort of level that they could counteract the engine's thrust.

 

[Son of Sluggish]

Where did i say anything in that post about ultimate speed? I was simply clarifying that you were of the view that you could have a situation where you had a treadmill that could create enough momentum through the rotational inertia of a plane's wheels to counteract the forward acceleration being produced by the thrust from the engines? And that I was of the view that the undercarriage would have self destructed long before the rotational inertia of the wheels reached any sort of level that they could counteract the engine's thrust.

The reverse momentum will begin at the moment of acceleration. In fact, its powerful point is when the wheel is at rest.

 

[Airhead]

Just so i'm clear you're saying that you could eventually create enough momentum through the rotational inertia of the turning wheels to accelerate the plane backwards at the same speed that the engines are accelerating it forwards??

I think i'll stick with my view that the entire undercarriage would have spectacularly self destructed well before you could get the wheels spinning anywhere near fast enough for the backward force produced through their rotational inertia to come anywhere close to the forward force produced by the plane's engine(s).

Also what exactly would be stopping the plane from accelerating forwards and taking off anyway while the treadmill is spinning the tyres upto a speed where the rotational inertia could possibly begin to have any effect?

OK..I've tried to explain this on several radio talk shows, so let me try here- If the conveyor belt is programed to turn at the EXACT SAME ROTATION the plane cannot possibly move forward. The conveyor is the counter to its forward movement; if the conveyor moves faster to counter act the forward thrust of the plane's movement it will stand still.

It has been suggested this question should be used to determine rather one has the fitness to cast a ballot, and frankly I agree.

 

[Krazeh]

The reverse momentum will begin at the moment of acceleration. In fact, its powerful point is when the wheel is at rest.

You'll have to excuse me if i've misread this but it seems to me that you're saying the backwards force acting on the wheel due to rotational inertia will be most powerful at the point where the wheel begins accelerating from rest? Rather than starting low and increasing as the wheel accelerates?

 

[Krazeh]

OK..I've tried to explain this on several radio talk shows, so let me try here- If the conveyor belt is programed to turn at the EXACT SAME ROTATION the plane cannot possibly move forward. The conveyor is the counter to its forward movement; if the conveyor moves faster to counter act the forward thrust of the plane's movement it will stand still.

You appear to be mixing up what the treadmill is doing. Is it matching the rotational speed of the wheels or is it matching the forward movement speed of the plane?

It has been suggested this question should be used to determine rather one has the fitness to cast a ballot, and frankly I agree.

To be honest before making such claims you should probably make sure you're considering the correct question first.

 

[FWNuke]

Okay, new premise.

Helicopter on a turntable.

 

[Krazeh]

Depends which way you're spinning it and how fast it can be spun.

 

[FWNuke]

Does it have a frictionless rotor?

 

[Son of Sluggish]

You'll have to excuse me if i've misread this but it seems to me that you're saying the backwards force acting on the wheel due to rotational inertia will be most powerful at the point where the wheel begins accelerating from rest? Rather than starting low and increasing as the wheel accelerates?

Indeed. The object at rest tends to stay at rest. The moment of movement is the most powerful because the ratio from non-movement to movement is one while movement to faster movement is a fraction. In order to maintain the same reverse momentum against the wheel it would have to increase its *acceleration* exponentially. If you could instantly accelerate the conveyor belt from zero to one-thousand miles per hour, even with the plane at full throttle, the plane would be thrown off the back of the conveyor with the plane cartwheeling over on its nose because the plane's freewheeling acceleration could not possibly keep up with the conveyor belts acceleration.

 

[Krazeh]

Does it have a frictionless rotor?

It'd be the wierdest helicopter i'd ever heard of if it did.

 

[Krazeh]

Indeed. The object at rest tends to stay at rest. The moment of movement is the most powerful because the ratio from non-movement to movement is one while movement to faster movement is a fraction. In order to maintain the same reverse momentum against the wheel it would have to increase its *acceleration* exponentially. If you could instantly accelerate the conveyor belt from zero to one-thousand miles per hour, even with the plane at full throttle, the plane would be thrown off the back of the conveyor with the plane cartwheeling over on its nose because the plane's freewheeling acceleration could not possibly keep up with the conveyor belts acceleration.

So if I understand this correctly, and what you've said previously, you think the thought experiment is essentially this:

If you have a indestructible treadmill (which can accelerate at an infinite rate to an infinite speed) on which is positioned a plane that has indestructible undercarriage (which can again accelerate at an infinite rate to an infinite speed) and you set the treadmill up in such a way that it prevent the plane from moving forward, can the plane take off?

Not really much of a thought experiment is it? Can a non-moving plane take off?? Gonna have to go with no there.

I think the problem here is that you've either misunderstood or have been provided with an incorrect version of the problem. For the problem to have been the one you appear to believe it to be you'd have to be consider a number of wholly unrealistic aspects and would still end up with teh question of whether a non-moving plane can take off.

The original question was, as far as i'm aware, posed in terms of the conveyor belt being set up in a way that it matches the plane's forward speed, altho I believe it was also described in terms of matching the plane's wheels speed so can see where it got confused down the line. Now obviously without ever being able to speak to the person who originally posed the question we'll never know for certain but it would certainly seem that having the treadmill match the plane's forward speed makes for a far better thought experiment as 1) people without a physics degree can actually make a reasonable attempt to answer it, and 2) it trips people up by the fact that the first thing people usually think of when considering hte movement of a vehicle with wheels is how a car moves along, which as we all know is very different to a plane.

 

[Son of Sluggish]

Here is a neat little video a intardnet buddy made to demonstrate moment of inertia and its potential to push a freewheeling object backward...

http://hallbuzz.com/movies/wheel_on_sander_250th.AVI

 

[Son of Sluggish]

So if I understand this correctly, and what you've said previously, you think the thought experiment is essentially this:

If you have a indestructible treadmill (which can accelerate at an infinite rate to an infinite speed) on which is positioned a plane that has indestructible undercarriage (which can again accelerate at an infinite rate to an infinite speed) and you set the treadmill up in such a way that it prevent the plane from moving forward, can the plane take off?

Not really much of a thought experiment is it? Can a non-moving plane take off?? Gonna have to go with no there.

I think the problem here is that you've either misunderstood or have been provided with an incorrect version of the problem. For the problem to have been the one you appear to believe it to be you'd have to be consider a number of wholly unrealistic aspects and would still end up with teh question of whether a non-moving plane can take off.

The original question was, as far as i'm aware, posed in terms of the conveyor belt being set up in a way that it matches the plane's forward speed, altho I believe it was also described in terms of matching the plane's wheels speed so can see where it got confused down the line. Now obviously without ever being able to speak to the person who originally posed the question we'll never know for certain but it would certainly seem that having the treadmill match the plane's forward speed makes for a far better thought experiment as 1) people without a physics degree can actually make a reasonable attempt to answer it, and 2) it trips people up by the fact that the first thing people usually think of when considering hte movement of a vehicle with wheels is how a car moves along, which as we all know is very different to a plane.

There have always been two forms of the question. In the simple one, where the conveyor belt matches the plane's speed, of course the plane will take off. In the second, the one where the conveyor belt matches the wheel speed, and the one which I have clearly stated that I am talking about and is clearly the most provocative, the plane cannot take off.

As I said from the onset, it is a mental exercise that cannot be replicated in the world. You guys have been too busy yucking it up at the stupid Yank to even read what I have been writing.

The plane doesn't fly.

 

[Krazeh]

There have always been two forms of the question. In the simple one, where the conveyor belt matches the plane's speed, of course the plane will take off. In the second, the one where the conveyor belt matches the wheel speed, and the one which I have clearly stated that I am talking about and is clearly the most provocative, the plane cannot take off.

I'm sorry but I disagree, it's not provocative in the slightest. How is creating a wholly unrealistic situation where it's the plane won't move and then asking if it could take off provocative? Not to mention that it requires using so many wholly unrealistic aspects and assumptions which aren't required when considering the conveyor belt matching the plane's speed. And to be perfectly honest it's only recently become clear that you were talking about the conveyor matching the wheel speed in terms of the wheel's rotational speed and not the wheel's speed along the ground. Without that distinction you could have been talking about either.

As I said from the onset, it is a mental exercise that cannot be replicated in the world. You guys have been too busy yucking it up at the stupid Yank to even read what I have been writing.

The plane doesn't fly.

Creating a situation in which you stop a plane from moving and then asking if it can take off isn't a mental exercise. The mental exercise in the whole "airplane on a treadmill" scenario has always been about coming to grips with the plane's forward movement being created in a different fashion to how most people would normally picture a wheeled vehicle creating forward motion, and grasping that the wheels actually disconnect the plane from the ground rather than creating the forward movement.

Anyway, on a final note, I did a bit of googling and have found what appears to be the first appearance of hte problem on an english speaking forum (it was originally posted on a russian forum but I don't speak russian and the poster on the english forum is apparently half-russian so i'll trust his translation, besides it's likely his post has been the basis for all the english speaking versions of hte problem). It was posted on a physics forum and states-

"A plane is standing on 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).

The question is:

Will the plane take off or not? Will it be able to run up and take off?"

(Source: PhysForum Science, Physics and Technology Discussion Forums -> Plane on conveyor... Will it ever take off?)

 

[StRaNgEdAyS]

The plane will continue to move forward regardless of the exponentially increasing speed of the conveyor and take off.

 

[Jail Bait]

The plane will continue to move forward regardless of the exponentially increasing speed of the conveyor and take off.

Spit the hook out SD

 

[Son of Sluggish]

I'm sorry but I disagree, it's not provocative in the slightest. How is creating a wholly unrealistic situation where it's the plane won't move and then asking if it could take off provocative? Not to mention that it requires using so many wholly unrealistic aspects and assumptions which aren't required when considering the conveyor belt matching the plane's speed. And to be perfectly honest it's only recently become clear that you were talking about the conveyor matching the wheel speed in terms of the wheel's rotational speed and not the wheel's speed along the ground. Without that distinction you could have been talking about either.

And the provocative part is in WHY the plane won't move. I bet your northern friend can't grasp why the plane can't move. After all, the engine isn't connected to the wheels!





Creating a situation in which you stop a plane from moving and then asking if it can take off isn't a mental exercise. The mental exercise in the whole "airplane on a treadmill" scenario has always been about coming to grips with the plane's forward movement being created in a different fashion to how most people would normally picture a wheeled vehicle creating forward motion, and grasping that the wheels actually disconnect the plane from the ground rather than creating the forward movement.

Anyway, on a final note, I did a bit of googling and have found what appears to be the first appearance of hte problem on an english speaking forum (it was originally posted on a russian forum but I don't speak russian and the poster on the english forum is apparently half-russian so i'll trust his translation, besides it's likely his post has been the basis for all the english speaking versions of hte problem). It was posted on a physics forum and states-

"A plane is standing on 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).

The question is:

Will the plane take off or not? Will it be able to run up and take off?"

(Source: PhysForum Science, Physics and Technology Discussion Forums -> Plane on conveyor... Will it ever take off?)

Yes... of course it was my fault... I was unclear...

https://forums.freddyshouse.com/general-2/242575-forum-fun-95.html#post3644424

My first post on the subject. Of course you and yours were too smug to actually read what the thick American wrote. The funny part? That idiot northerner will still try to argue why I'm wrong.

Whatever you felt the scenario was was from your own smugness. If you had read the first post I made on the subject there would no question.

 

[SWtarget]

A car in a vacuum with frictionless bearings coasting on a flat surface will slow down and stop because of rolling friction between the road and the tire's surface.

The friction of the road/tires is applying lateral resistance to the vehicle's forward motion.

Would this whole discussion be similar or dissimilar to the FW thread a while back as to whether anti-lock brakes stop a car faster than locking the wheels?