FabSwingers.com mobile

Join us FREE, we're FREE to use

Web's largest swingers site since 2006.

Already registered?
Login here

Back to forum list
Back to The Lounge

That sodding 'plane!

Jump to newest
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk

Copied from a link I can't share. For the love of all things horny, read it until you understand it!

I created this blog specifically to make this post. It may be the only post I ever write, but since human ignorance is seemingly unbounded, perhaps it won't be.

I thought that today would be a monumental day for this topic. Today, the Mythbusters debuted their long-awaited "Airplane on a treadmill" episode. For years, physics teachers around the world have cringed in horror at heated internet debates concerning a ludicrous thought experiment. Sadly, half of them recoiled in disgust at the correct arguments. Forum posters signed their names with such epithets as "Ph.D. Aerospace Engineer" and "20-year pilot." Somewhat tellingly, these ego-boosters were most often employed by those delivering the wrong answers. Mythbusters finally attempted to end the insanity by performing the experiment themselves.

AND YET...

The debate rages on. Even after being shown seemingly conclusive evidence of the other side's argument, forum-goers from near and far continued to staunchly defend their own theories.

Here and now, the debate will end. I intend this long-winded article to be the definitive answer to the great AOAT conundrum. No further debate is necessary - simply direct the ignorant people to this page, tell them to read it, and let's all get on with answering more intriguing questions, like does P = NP?

For those of you just joining us, "Airplane On A Treadmill," also known as "Airplane on a Conveyor Belt," is a thought experiment in physics. Some consider it a litmus test for assessing one's knowledge of airplane physics. In its most basic form, the experiment is worded thusly:

A plane is standing on a large treadmill or conveyor belt. The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the plane speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction). Can the plane take off?

The question suffers from many rewordings that muddle much of the debate about the thought experiment. The basic idea is that there's a plane, on a treadmill, and we're going to run the treadmill backwards in an attempt to stop the plane from taking off. And here, at the very beginning of this explanation, is the definitive answer. There are in fact two correct answers to this question:

- No, the plane can't take off.

- Yes, the plane can take off.

Fooled you! But that's just the point. The experiment is meaningless, and the passionate internet debates more so, if we cannot agree on what is truly meant by the question. But don't worry, I won't pull a Lost on you - I do intend to give a truly airtight answer later on. For now though, we need to debate semantics.

Really, we do.

You see, the AOAT confusion all arises from misses - misconceptions, misinterpretations, and misunderstandings. Consider three rewordings of the question:

1) An airplane is sitting at rest on a very powerful treadmill. You are at the controls of the treadmill, while I am at the controls of the airplane. On some signal, I begin to attempt to take flight in the plane, and you attempt to match my speed to try to keep me stationary. Will the plane take off?

2) An airplane is sitting at rest on a very powerful treadmill. You are at the controls of the treadmill, while I am at the controls of the airplane. On some signal, I throttle up the airplane and you turn on the treadmill, and we conspire by our joint effort to try to keep the plane stationary relative to the ground. Will the plane take off?

3) An airplane is sitting at rest on a very powerful treadmill. You are at the controls of the treadmill, while I am at the controls of the airplane. On some signal, I attempt to take flight in the plane, but you match my speed with the treadmill and keep me stationary relative to the ground. Will the plane take off?

Here are the absolute, 100%, bet-your-life-on-it answers to these rewordings:

Yes.

No.

Whoever asked this question is an idiot.

And that's about all this debate comes down to, folks. If we could all agree on one set of rules for the thought experiment, then we ought to be able to make the explanation of the answer clear. As it stands, normally one side has interpretation (1) in mind, and argues vehemently with someone else who has interpretation (2) in mind, and the whole thing blows up into a senseless squabble.

Here are the three core facts that are rock-solid:

A) If the plane remains stationary relative to the ground, it will not take off.

B) If the plane moves relative to the ground, it will take off.

C) The person operating the conveyor belt CANNOT by himself make the plane remain stationary relative to the ground.

(EDIT: Really, you should substitute the word "air" for ground in the above facts. I use "ground" throughout this post because of a consistent mistake made by "no-flys" in their assumption that the plane remains stationary. It doesn't remain stationary, relative to the ground or the air. The important point is that it moves relative to the air, not the ground, but I'm assuming throughout this post that there is no significant tailwind or headwind. I discuss the implications of this briefly in the section about windtunnels.)

That's about all you need to know to argue whichever interpretation is appropriate. I'll discuss why these facts are true in a moment. In the meantime, look back at the three re-wordings of the question above.

In (1), the key phrase is "you attempt to match my speed to try to keep me stationary." Since we know from fact (C) that you cannot keep me stationary, it follows from (B) that I will take off successfully.

In (2), we conspire together to keep the plane stationary. This is possible, albeit stupid. We know from fact (A) that I will not take off.

In (3) - and this is the important part - the actions being described are impossible. We know from (C) that the conveyor operator cannot keep the plane stationary. The most powerful conveyor belt in the world couldn't do it. David Copperfield couldn't do it. It can't be done. Only if the pilot "plays along" can the plane be made to remain stationary.

Unfortunately, most of the "no-flys" - the label given to those who argue that the plane won't take off - are assuming that interpretation (3) is what is being asked. They accept that the plane remains stationary, and say it won't take off. The "will-flys" know that the plane can't remain stationary, and say it will take off. Add to the mix a few people who see that in one way, the plane could be forced to be stationary by some pilot-conveyor cooperation, and you've got a deadly internet forum explosion cocktail.

Let's examine the physics behind the three key facts, so that there will be no doubt as to their validity. The first two are pretty easy to follow. Airplanes create lift by causing air to flow over their wings. This airflow is caused by the motion of the wings relative to the air - that can happen in two ways. The first way is to move the plane forward through the air. The second is to blow air against the plane and over the wings. As far as the plane is concerned, these two scenarios are equivalent. So you could put a plane in a very powerful wind tunnel, blow air over its wings, and have it fly stationary relative to the ground. But that's another question.

In our treadmill scenario, the air is stationary relative to the ground, so the plane has to move relative to the ground in order to gain flight. If it doesn't move, it simply won't fly. There will be no airflow over the wings, and there will be no lift. A lot of people get confused here, and think that the original thought experiment is some sort of trick question, and that the propeller of the airplane, or possibly the jet engines, will be blowing air backwards over the wings, which will create lift. While there will be a certain amount of airflow created by the propeller or engines, it is not enough to create flight. I promise you, that's not what the question is asking.

Really, I promise. Please, please stop talking about airflow created by the prop. It isn't part of the question.

So we have facts (A) and (B) well taken care of. If the plane moves, it flies. If it doesn't move, it doesn't fly. The real question is, will it move? Again, the answer is unambiguous - if the pilot doesn't try to make the plane stay still, it won't. If he does, it will. This is always, always the part that confuses people, so stick with me for a few more paragraphs.

When a plane is sitting on a runway, it moves by using its engines. It does not move by any sort of motorized wheel. The propellers or jets create thrust that pushes against the surrounding air and causes the plane to move forward. A plane wouldn't move at all in a vacuum chamber. Compare this to a car, which moves by applying torque to the wheels. A car would drive just fine in a vacuum chamber - at least, as long as the driver could survive (and technically, it would need some sort of air reservoir to provide something to mix with the fuel. An electric car wouldn't have this problem.) However, a car could not drive on a frictionless surface - imagine, for example, that you had your car on a super slippery frozen lake. As you hit the gas, the wheels would simply spin and spin in place, and the car wouldn't move forward. You may even have firsthand experience with this situation if you've ever gotten stuck in a snow bank. In contrast, a plane would have no trouble moving on a frictionless surface. The jet engines or propeller would still push against the air, and the plane would still move forward. If it were on a truly frictionless surface, then you would see the wheels sliding along the ground, not rotating.

I hope those two scenarios clearly illustrate the difference in motive force between cars and planes. Cars create their forward movement from torque applied to the wheels, which push against the ground and create forward motion from friction. Planes create their forward movement from thrust applied to the air, which pushes the plane forward regardless of the surface it is on.

Imagine a plane without wheels. The fuselage would sit on the runway, and as you fired up the engines, it would skid spectacularly along the runway, possibly spewing sparks in its wake and doing quite a number on the body of the aircraft. No matter how fast it was going, the frictional force against the airplane would be constant; friction does not depend on speed! If the engines were strong enough to get the plane up to the critical take-off speed, then it would still take off. The only reason planes have wheels is to reduce this sliding friction. The wheels roll along the runway instead of sliding, and the only friction that the plane feels is in the bearings of the wheels. This is substantially less than the friction that a sliding fuselage would create, and it's a much smoother ride for the passengers as well.

(Edit: Technically, there are some factors that would make the friction change with speed. The classic idealized model called "coulomb friction" doesn't really apply to bearings. As the bearings spun faster and faster, they would generate heat, which would increase the friction slightly on the wheels. However, it would never be enough force to prevent take-off. The only time this would prevent take-off is if the wheels locked up or broke off, and then we'd have a much bigger problem and catastrophic failure.)

So what does this all have to do with treadmills? Well, now let's place our plane on that treadmill and see what happens. If the wheels were perfect - that is, there is no friction in the bearings (and no deformation of the wheels as they spin) - then something interesting happens. When we turn on the treadmill, the plane stays stationary on its own. The wheels simply spin along the track, and impart no force to the plane. If you had a car with frictionless axles, and you disconnected the whole drive train, the same thing would happen to your car.

The only reason that a plane or a car moves backwards on a treadmill is that the wheels are somehow partially locked to the axles. In a plane, this is because of minor friction in the bearings. In a car, it's because of the drive train. If you want the car to stay still, you have to turn the drive train at the proper speed. If you want the plane to stay still, you have to overcome the minor bearing friction. And again, since friction does not change with speed, you don't have to exert any more force at higher speeds. If you run the treadmill at 5mph and turn on the plane's engines just slightly, they will provide enough thrust, pushing against the air, to keep the plane still. If you then increase the treadmill speed to 500 mph, you won't need to adjust the throttle on the airplane - it will remain stationary. That's because it's seeing the same frictional force that it was at 5mph. Thus, it doesn't matter how fast the treadmill is moving - if the pilot does not want to remain stationary, then he won't. It only uses the very first bit of power from the engines to keep the plane stationary. As the throttle is increased from that point, it moves forward just as it would on any other runway. It's pushing against the stationary air!

If you don't believe me, imagine this (or even try it at home): you're standing on a skateboard on a treadmill. You hold onto the handrails of the treadmill and turn it on. Of course, you'll remain stationary (relative to the ground). In fact, you only need to use a very light touch to stay stationary - perhaps a few fingers pressed against the handrails. Crank up the treadmill speed as high as you like. You'll still only need the same light touch to remain stationary. At any time you like, you can move forward - closer to the treadmill console - by simple pulling on the handrails. If you had a jet engine, or super-strong hairdryer, you could use this to propel yourself forward instead of holding onto the handrails. In fact, if you're really careful, you might be able to do this at home with a skateboard and a leafbower, but I doubt you'll have a sensitive enough control of your leafblower thrust to get yourself to remain stationary.

So you see (oh please tell me you see), the conveyor operator cannot force the plane to remain stationary. And if the plane isn't stationary, it can take off.

And yes, if we interpret the question in a different way, and assume that for some reason the pilot is colluding with the conveyor operator and keeping the plane stationary, then the plane can't take off.

But what is the question really getting at, anyway? There are really two "spirits" of the question. In the first, we're asking "can a plane take off with no runway, if I replace the runway with a treadmill?" The answer, as we know now, is no. The plane must move relative to the ground in order to take off. In another deep-meaning of the question, we're asking "is it possible to prevent a plane from taking off, by moving the runway backwards under it?" The answer again is no, you can't prevent it from taking off.

The interesting thing about all this is that in both scenarios, you'd wind up with a plane moving relative to the ground. In the first scenario, you might think you're being clever by allowing a plane to take off from a very small field, by using a treadmill runway. If you actually tried it, you'd be attempting to take off, so the plane would move, and would likely crash into something, or fall off a cliff, or suffer some other catastrophe that you were trying to avoid with questionable physics. In the second scenario, you'd give the plane plenty of room and safety to take off, but attempt to play a practical joke on the pilot by moving the runway backwards, and you'd wind up with a plane in flight, much to your chagrin.

When the "no-flys" saw the Mythbusters episode, they all complained that it wasn't done properly, because the plane didn't remain stationary. But think about it for a moment. No, really think about it, don't just spout about Bernoulli's principle and airflow and all that. In what possible scenario would the plane actually stay still? The only way this can happen is if the pilot is trying to stay still, and this only happens if he just barely applies the throttle, making no attempt to take off. This makes no sense. Either you're trying to prevent him from taking off with your clever and misinformed use of a conveyor belt, or he's trying to defy physics by taking off in a too-small area. There is no scenario in which the plane would realistically stay still. We know what would happen if it did - it would sit on the runway, not taking off, and we'd all stare at each other in an all-too-short silence punctuated by loud exclamations of "I told you so!". But that's not really what the thought experiment is getting at, no matter how you reasonably interpret it. Luckily for all of us, if we agree on the interpretation, reasonable or not, we should all agree on the answer.

So let's get back to the next great internet debate, shall we?

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk

tl;dr The 'plane will take off UNLESS the pilot coludes in order to keep the 'plane stationary with respect to the ground.

The belt CANNOT keep the plane stationery with respect to the ground without the assistance of the pilot.

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk

colludes*

Reply privatelyReply in forumReply +quote
 

By *lkDomWhtSubBiCpleCouple
over a year ago

Somewhere / Everywhere /Kinksville

Reply privatelyReply in forumReply +quote
 

By (user no longer on site)
over a year ago

Can't argue with that

Reply privatelyReply in forumReply +quote
 

By (user no longer on site)
over a year ago

Yeah - wot she said - I think - well mostly...

But it's still unresolved whether two African swallows can fly and carry a coconut between them...?

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk


"Can't argue with that "

I'm fairly sure plenty will!

Reply privatelyReply in forumReply +quote
 

By (user no longer on site)
over a year ago

Longest post of the year winner.

#notsuitableifyouhaveshortattentionspan.

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk


"Longest post of the year winner.

#notsuitableifyouhaveshortattentionspan. "

I did do a tl;dr

Reply privatelyReply in forumReply +quote
 

By (user no longer on site)
over a year ago

That's all well and good but can you put a Rowntrees fruit pastille in ya mouth without chewing it.

Reply privatelyReply in forumReply +quote
 

By *avrick15Man
over a year ago

glasgow

Nicely put and good breasts by the way, top marks on both

Reply privatelyReply in forumReply +quote
 

By (user no longer on site)
over a year ago

Can i have my 15 minutes back please? (slow reader)

Reply privatelyReply in forumReply +quote
 

By *ureTemptationWoman
over a year ago

Off the grid


"Yeah - wot she said - I think - well mostly...

But it's still unresolved whether two African swallows can fly and carry a coconut between them...?

"

They carry it by the husk!

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk


"That's all well and good but can you put a Rowntrees fruit pastille in ya mouth without chewing it. "

No.

I'm on a fucking diet

Reply privatelyReply in forumReply +quote
 

By (user no longer on site)
over a year ago

Big error in your statements.

For it to take off you state the plane is "stationary relative to the ground, but not to the air". Since you say there is no wind effect then the air is ALSO STATIONARY relative to the ground and, therefore, relative to the plane.

On take off a plane has to roll forward on its wheels. The conveyor is programmed to move backwards at same speed as wheels. In ALL of your re-wordings. (The initial thought experiment was not reworded....some on here have tried to do it). Therefore the plane doesn't move. Relative to ground OR relative to air. It is going nowhere!

Reply privatelyReply in forumReply +quote
 

By *aucy tiggerWoman
over a year ago

Back where I belong

I'm still getting excited about all the thrusts

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk


"Big error in your statements.

For it to take off you state the plane is "stationary relative to the ground, but not to the air". Since you say there is no wind effect then the air is ALSO STATIONARY relative to the ground and, therefore, relative to the plane.

On take off a plane has to roll forward on its wheels. The conveyor is programmed to move backwards at same speed as wheels. In ALL of your re-wordings. (The initial thought experiment was not reworded....some on here have tried to do it). Therefore the plane doesn't move. Relative to ground OR relative to air. It is going nowhere!"

You've totally missed the point.

And these are not "my" rewordings, which is something you've also apparently missed.

Reply privatelyReply in forumReply +quote
 

By (user no longer on site)
over a year ago

I'm more worried that this is gonna descend into 'Physics....vol' 4'

Reply privatelyReply in forumReply +quote
 

By *avrick15Man
over a year ago

glasgow


"I'm more worried that this is gonna descend into 'Physics....vol' 4' "

Shhhhhh

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk

PS the 'plane DOES move except when the pilot colludes to stop it. Please read the article again until you understand why.

Reply privatelyReply in forumReply +quote
 

By (user no longer on site)
over a year ago


"I'm more worried that this is gonna descend into 'Physics....vol' 4'

Shhhhhh "

It appears to be to late

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk


"I'm more worried that this is gonna descend into 'Physics....vol' 4' "

If it does, people failed to follow the direction to read the article until the understand it, or are continuing to argue without understanding the situation at all.

Not that it's at all unusual here.

Reply privatelyReply in forumReply +quote
 

By (user no longer on site)
over a year ago

Zzzz...

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk

OIIIIII YOU ON THE PHYSICS THREAD!!!

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk

*cough*

Reply privatelyReply in forumReply +quote
 

By (user no longer on site)
over a year ago


"Copied from a link I can't share. For the love of all things horny, read it until you understand it!

I created this blog specifically to make this post. It may be the only post I ever write, but since human ignorance is seemingly unbounded, perhaps it won't be.

I thought that today would be a monumental day for this topic. Today, the Mythbusters debuted their long-awaited "Airplane on a treadmill" episode. For years, physics teachers around the world have cringed in horror at heated internet debates concerning a ludicrous thought experiment. Sadly, half of them recoiled in disgust at the correct arguments. Forum posters signed their names with such epithets as "Ph.D. Aerospace Engineer" and "20-year pilot." Somewhat tellingly, these ego-boosters were most often employed by those delivering the wrong answers. Mythbusters finally attempted to end the insanity by performing the experiment themselves.

AND YET...

The debate rages on. Even after being shown seemingly conclusive evidence of the other side's argument, forum-goers from near and far continued to staunchly defend their own theories.

Here and now, the debate will end. I intend this long-winded article to be the definitive answer to the great AOAT conundrum. No further debate is necessary - simply direct the ignorant people to this page, tell them to read it, and let's all get on with answering more intriguing questions, like does P = NP?

For those of you just joining us, "Airplane On A Treadmill," also known as "Airplane on a Conveyor Belt," is a thought experiment in physics. Some consider it a litmus test for assessing one's knowledge of airplane physics. In its most basic form, the experiment is worded thusly:

A plane is standing on a large treadmill or conveyor belt. The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the plane speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction). Can the plane take off?

The question suffers from many rewordings that muddle much of the debate about the thought experiment. The basic idea is that there's a plane, on a treadmill, and we're going to run the treadmill backwards in an attempt to stop the plane from taking off. And here, at the very beginning of this explanation, is the definitive answer. There are in fact two correct answers to this question:

- No, the plane can't take off.

- Yes, the plane can take off.

Fooled you! But that's just the point. The experiment is meaningless, and the passionate internet debates more so, if we cannot agree on what is truly meant by the question. But don't worry, I won't pull a Lost on you - I do intend to give a truly airtight answer later on. For now though, we need to debate semantics.

Really, we do.

You see, the AOAT confusion all arises from misses - misconceptions, misinterpretations, and misunderstandings. Consider three rewordings of the question:

1) An airplane is sitting at rest on a very powerful treadmill. You are at the controls of the treadmill, while I am at the controls of the airplane. On some signal, I begin to attempt to take flight in the plane, and you attempt to match my speed to try to keep me stationary. Will the plane take off?

2) An airplane is sitting at rest on a very powerful treadmill. You are at the controls of the treadmill, while I am at the controls of the airplane. On some signal, I throttle up the airplane and you turn on the treadmill, and we conspire by our joint effort to try to keep the plane stationary relative to the ground. Will the plane take off?

3) An airplane is sitting at rest on a very powerful treadmill. You are at the controls of the treadmill, while I am at the controls of the airplane. On some signal, I attempt to take flight in the plane, but you match my speed with the treadmill and keep me stationary relative to the ground. Will the plane take off?

Here are the absolute, 100%, bet-your-life-on-it answers to these rewordings:

Yes.

No.

Whoever asked this question is an idiot.

And that's about all this debate comes down to, folks. If we could all agree on one set of rules for the thought experiment, then we ought to be able to make the explanation of the answer clear. As it stands, normally one side has interpretation (1) in mind, and argues vehemently with someone else who has interpretation (2) in mind, and the whole thing blows up into a senseless squabble.

Here are the three core facts that are rock-solid:

A) If the plane remains stationary relative to the ground, it will not take off.

B) If the plane moves relative to the ground, it will take off.

C) The person operating the conveyor belt CANNOT by himself make the plane remain stationary relative to the ground.

(EDIT: Really, you should substitute the word "air" for ground in the above facts. I use "ground" throughout this post because of a consistent mistake made by "no-flys" in their assumption that the plane remains stationary. It doesn't remain stationary, relative to the ground or the air. The important point is that it moves relative to the air, not the ground, but I'm assuming throughout this post that there is no significant tailwind or headwind. I discuss the implications of this briefly in the section about windtunnels.)

That's about all you need to know to argue whichever interpretation is appropriate. I'll discuss why these facts are true in a moment. In the meantime, look back at the three re-wordings of the question above.

In (1), the key phrase is "you attempt to match my speed to try to keep me stationary." Since we know from fact (C) that you cannot keep me stationary, it follows from (B) that I will take off successfully.

In (2), we conspire together to keep the plane stationary. This is possible, albeit stupid. We know from fact (A) that I will not take off.

In (3) - and this is the important part - the actions being described are impossible. We know from (C) that the conveyor operator cannot keep the plane stationary. The most powerful conveyor belt in the world couldn't do it. David Copperfield couldn't do it. It can't be done. Only if the pilot "plays along" can the plane be made to remain stationary.

Unfortunately, most of the "no-flys" - the label given to those who argue that the plane won't take off - are assuming that interpretation (3) is what is being asked. They accept that the plane remains stationary, and say it won't take off. The "will-flys" know that the plane can't remain stationary, and say it will take off. Add to the mix a few people who see that in one way, the plane could be forced to be stationary by some pilot-conveyor cooperation, and you've got a deadly internet forum explosion cocktail.

Let's examine the physics behind the three key facts, so that there will be no doubt as to their validity. The first two are pretty easy to follow. Airplanes create lift by causing air to flow over their wings. This airflow is caused by the motion of the wings relative to the air - that can happen in two ways. The first way is to move the plane forward through the air. The second is to blow air against the plane and over the wings. As far as the plane is concerned, these two scenarios are equivalent. So you could put a plane in a very powerful wind tunnel, blow air over its wings, and have it fly stationary relative to the ground. But that's another question.

In our treadmill scenario, the air is stationary relative to the ground, so the plane has to move relative to the ground in order to gain flight. If it doesn't move, it simply won't fly. There will be no airflow over the wings, and there will be no lift. A lot of people get confused here, and think that the original thought experiment is some sort of trick question, and that the propeller of the airplane, or possibly the jet engines, will be blowing air backwards over the wings, which will create lift. While there will be a certain amount of airflow created by the propeller or engines, it is not enough to create flight. I promise you, that's not what the question is asking.

Really, I promise. Please, please stop talking about airflow created by the prop. It isn't part of the question.

So we have facts (A) and (B) well taken care of. If the plane moves, it flies. If it doesn't move, it doesn't fly. The real question is, will it move? Again, the answer is unambiguous - if the pilot doesn't try to make the plane stay still, it won't. If he does, it will. This is always, always the part that confuses people, so stick with me for a few more paragraphs.

When a plane is sitting on a runway, it moves by using its engines. It does not move by any sort of motorized wheel. The propellers or jets create thrust that pushes against the surrounding air and causes the plane to move forward. A plane wouldn't move at all in a vacuum chamber. Compare this to a car, which moves by applying torque to the wheels. A car would drive just fine in a vacuum chamber - at least, as long as the driver could survive (and technically, it would need some sort of air reservoir to provide something to mix with the fuel. An electric car wouldn't have this problem.) However, a car could not drive on a frictionless surface - imagine, for example, that you had your car on a super slippery frozen lake. As you hit the gas, the wheels would simply spin and spin in place, and the car wouldn't move forward. You may even have firsthand experience with this situation if you've ever gotten stuck in a snow bank. In contrast, a plane would have no trouble moving on a frictionless surface. The jet engines or propeller would still push against the air, and the plane would still move forward. If it were on a truly frictionless surface, then you would see the wheels sliding along the ground, not rotating.

I hope those two scenarios clearly illustrate the difference in motive force between cars and planes. Cars create their forward movement from torque applied to the wheels, which push against the ground and create forward motion from friction. Planes create their forward movement from thrust applied to the air, which pushes the plane forward regardless of the surface it is on.

Imagine a plane without wheels. The fuselage would sit on the runway, and as you fired up the engines, it would skid spectacularly along the runway, possibly spewing sparks in its wake and doing quite a number on the body of the aircraft. No matter how fast it was going, the frictional force against the airplane would be constant; friction does not depend on speed! If the engines were strong enough to get the plane up to the critical take-off speed, then it would still take off. The only reason planes have wheels is to reduce this sliding friction. The wheels roll along the runway instead of sliding, and the only friction that the plane feels is in the bearings of the wheels. This is substantially less than the friction that a sliding fuselage would create, and it's a much smoother ride for the passengers as well.

(Edit: Technically, there are some factors that would make the friction change with speed. The classic idealized model called "coulomb friction" doesn't really apply to bearings. As the bearings spun faster and faster, they would generate heat, which would increase the friction slightly on the wheels. However, it would never be enough force to prevent take-off. The only time this would prevent take-off is if the wheels locked up or broke off, and then we'd have a much bigger problem and catastrophic failure.)

So what does this all have to do with treadmills? Well, now let's place our plane on that treadmill and see what happens. If the wheels were perfect - that is, there is no friction in the bearings (and no deformation of the wheels as they spin) - then something interesting happens. When we turn on the treadmill, the plane stays stationary on its own. The wheels simply spin along the track, and impart no force to the plane. If you had a car with frictionless axles, and you disconnected the whole drive train, the same thing would happen to your car.

The only reason that a plane or a car moves backwards on a treadmill is that the wheels are somehow partially locked to the axles. In a plane, this is because of minor friction in the bearings. In a car, it's because of the drive train. If you want the car to stay still, you have to turn the drive train at the proper speed. If you want the plane to stay still, you have to overcome the minor bearing friction. And again, since friction does not change with speed, you don't have to exert any more force at higher speeds. If you run the treadmill at 5mph and turn on the plane's engines just slightly, they will provide enough thrust, pushing against the air, to keep the plane still. If you then increase the treadmill speed to 500 mph, you won't need to adjust the throttle on the airplane - it will remain stationary. That's because it's seeing the same frictional force that it was at 5mph. Thus, it doesn't matter how fast the treadmill is moving - if the pilot does not want to remain stationary, then he won't. It only uses the very first bit of power from the engines to keep the plane stationary. As the throttle is increased from that point, it moves forward just as it would on any other runway. It's pushing against the stationary air!

If you don't believe me, imagine this (or even try it at home): you're standing on a skateboard on a treadmill. You hold onto the handrails of the treadmill and turn it on. Of course, you'll remain stationary (relative to the ground). In fact, you only need to use a very light touch to stay stationary - perhaps a few fingers pressed against the handrails. Crank up the treadmill speed as high as you like. You'll still only need the same light touch to remain stationary. At any time you like, you can move forward - closer to the treadmill console - by simple pulling on the handrails. If you had a jet engine, or super-strong hairdryer, you could use this to propel yourself forward instead of holding onto the handrails. In fact, if you're really careful, you might be able to do this at home with a skateboard and a leafbower, but I doubt you'll have a sensitive enough control of your leafblower thrust to get yourself to remain stationary.

So you see (oh please tell me you see), the conveyor operator cannot force the plane to remain stationary. And if the plane isn't stationary, it can take off.

And yes, if we interpret the question in a different way, and assume that for some reason the pilot is colluding with the conveyor operator and keeping the plane stationary, then the plane can't take off.

But what is the question really getting at, anyway? There are really two "spirits" of the question. In the first, we're asking "can a plane take off with no runway, if I replace the runway with a treadmill?" The answer, as we know now, is no. The plane must move relative to the ground in order to take off. In another deep-meaning of the question, we're asking "is it possible to prevent a plane from taking off, by moving the runway backwards under it?" The answer again is no, you can't prevent it from taking off.

The interesting thing about all this is that in both scenarios, you'd wind up with a plane moving relative to the ground. In the first scenario, you might think you're being clever by allowing a plane to take off from a very small field, by using a treadmill runway. If you actually tried it, you'd be attempting to take off, so the plane would move, and would likely crash into something, or fall off a cliff, or suffer some other catastrophe that you were trying to avoid with questionable physics. In the second scenario, you'd give the plane plenty of room and safety to take off, but attempt to play a practical joke on the pilot by moving the runway backwards, and you'd wind up with a plane in flight, much to your chagrin.

When the "no-flys" saw the Mythbusters episode, they all complained that it wasn't done properly, because the plane didn't remain stationary. But think about it for a moment. No, really think about it, don't just spout about Bernoulli's principle and airflow and all that. In what possible scenario would the plane actually stay still? The only way this can happen is if the pilot is trying to stay still, and this only happens if he just barely applies the throttle, making no attempt to take off. This makes no sense. Either you're trying to prevent him from taking off with your clever and misinformed use of a conveyor belt, or he's trying to defy physics by taking off in a too-small area. There is no scenario in which the plane would realistically stay still. We know what would happen if it did - it would sit on the runway, not taking off, and we'd all stare at each other in an all-too-short silence punctuated by loud exclamations of "I told you so!". But that's not really what the thought experiment is getting at, no matter how you reasonably interpret it. Luckily for all of us, if we agree on the interpretation, reasonable or not, we should all agree on the answer.

So let's get back to the next great internet debate, shall we?"

I don't have anything to say, I just enjoy making people scroll unnecessarily

Reply privatelyReply in forumReply +quote
 

By *ranny-CrumpetWoman
over a year ago

The Town by The Cross


"Copied from a link I can't share. For the love of all things horny, read it until you understand it!

I created this blog specifically to make this post. It may be the only post I ever write, but since human ignorance is seemingly unbounded, perhaps it won't be.

I thought that today would be a monumental day for this topic. Today, the Mythbusters debuted their long-awaited "Airplane on a treadmill" episode. For years, physics teachers around the world have cringed in horror at heated internet debates concerning a ludicrous thought experiment. Sadly, half of them recoiled in disgust at the correct arguments. Forum posters signed their names with such epithets as "Ph.D. Aerospace Engineer" and "20-year pilot." Somewhat tellingly, these ego-boosters were most often employed by those delivering the wrong answers. Mythbusters finally attempted to end the insanity by performing the experiment themselves.

AND YET...

The debate rages on. Even after being shown seemingly conclusive evidence of the other side's argument, forum-goers from near and far continued to staunchly defend their own theories.

Here and now, the debate will end. I intend this long-winded article to be the definitive answer to the great AOAT conundrum. No further debate is necessary - simply direct the ignorant people to this page, tell them to read it, and let's all get on with answering more intriguing questions, like does P = NP?

For those of you just joining us, "Airplane On A Treadmill," also known as "Airplane on a Conveyor Belt," is a thought experiment in physics. Some consider it a litmus test for assessing one's knowledge of airplane physics. In its most basic form, the experiment is worded thusly:

A plane is standing on a large treadmill or conveyor belt. The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the plane speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction). Can the plane take off?

The question suffers from many rewordings that muddle much of the debate about the thought experiment. The basic idea is that there's a plane, on a treadmill, and we're going to run the treadmill backwards in an attempt to stop the plane from taking off. And here, at the very beginning of this explanation, is the definitive answer. There are in fact two correct answers to this question:

- No, the plane can't take off.

- Yes, the plane can take off.

Fooled you! But that's just the point. The experiment is meaningless, and the passionate internet debates more so, if we cannot agree on what is truly meant by the question. But don't worry, I won't pull a Lost on you - I do intend to give a truly airtight answer later on. For now though, we need to debate semantics.

Really, we do.

You see, the AOAT confusion all arises from misses - misconceptions, misinterpretations, and misunderstandings. Consider three rewordings of the question:

1) An airplane is sitting at rest on a very powerful treadmill. You are at the controls of the treadmill, while I am at the controls of the airplane. On some signal, I begin to attempt to take flight in the plane, and you attempt to match my speed to try to keep me stationary. Will the plane take off?

2) An airplane is sitting at rest on a very powerful treadmill. You are at the controls of the treadmill, while I am at the controls of the airplane. On some signal, I throttle up the airplane and you turn on the treadmill, and we conspire by our joint effort to try to keep the plane stationary relative to the ground. Will the plane take off?

3) An airplane is sitting at rest on a very powerful treadmill. You are at the controls of the treadmill, while I am at the controls of the airplane. On some signal, I attempt to take flight in the plane, but you match my speed with the treadmill and keep me stationary relative to the ground. Will the plane take off?

Here are the absolute, 100%, bet-your-life-on-it answers to these rewordings:

Yes.

No.

Whoever asked this question is an idiot.

And that's about all this debate comes down to, folks. If we could all agree on one set of rules for the thought experiment, then we ought to be able to make the explanation of the answer clear. As it stands, normally one side has interpretation (1) in mind, and argues vehemently with someone else who has interpretation (2) in mind, and the whole thing blows up into a senseless squabble.

Here are the three core facts that are rock-solid:

A) If the plane remains stationary relative to the ground, it will not take off.

B) If the plane moves relative to the ground, it will take off.

C) The person operating the conveyor belt CANNOT by himself make the plane remain stationary relative to the ground.

(EDIT: Really, you should substitute the word "air" for ground in the above facts. I use "ground" throughout this post because of a consistent mistake made by "no-flys" in their assumption that the plane remains stationary. It doesn't remain stationary, relative to the ground or the air. The important point is that it moves relative to the air, not the ground, but I'm assuming throughout this post that there is no significant tailwind or headwind. I discuss the implications of this briefly in the section about windtunnels.)

That's about all you need to know to argue whichever interpretation is appropriate. I'll discuss why these facts are true in a moment. In the meantime, look back at the three re-wordings of the question above.

In (1), the key phrase is "you attempt to match my speed to try to keep me stationary." Since we know from fact (C) that you cannot keep me stationary, it follows from (B) that I will take off successfully.

In (2), we conspire together to keep the plane stationary. This is possible, albeit stupid. We know from fact (A) that I will not take off.

In (3) - and this is the important part - the actions being described are impossible. We know from (C) that the conveyor operator cannot keep the plane stationary. The most powerful conveyor belt in the world couldn't do it. David Copperfield couldn't do it. It can't be done. Only if the pilot "plays along" can the plane be made to remain stationary.

Unfortunately, most of the "no-flys" - the label given to those who argue that the plane won't take off - are assuming that interpretation (3) is what is being asked. They accept that the plane remains stationary, and say it won't take off. The "will-flys" know that the plane can't remain stationary, and say it will take off. Add to the mix a few people who see that in one way, the plane could be forced to be stationary by some pilot-conveyor cooperation, and you've got a deadly internet forum explosion cocktail.

Let's examine the physics behind the three key facts, so that there will be no doubt as to their validity. The first two are pretty easy to follow. Airplanes create lift by causing air to flow over their wings. This airflow is caused by the motion of the wings relative to the air - that can happen in two ways. The first way is to move the plane forward through the air. The second is to blow air against the plane and over the wings. As far as the plane is concerned, these two scenarios are equivalent. So you could put a plane in a very powerful wind tunnel, blow air over its wings, and have it fly stationary relative to the ground. But that's another question.

In our treadmill scenario, the air is stationary relative to the ground, so the plane has to move relative to the ground in order to gain flight. If it doesn't move, it simply won't fly. There will be no airflow over the wings, and there will be no lift. A lot of people get confused here, and think that the original thought experiment is some sort of trick question, and that the propeller of the airplane, or possibly the jet engines, will be blowing air backwards over the wings, which will create lift. While there will be a certain amount of airflow created by the propeller or engines, it is not enough to create flight. I promise you, that's not what the question is asking.

Really, I promise. Please, please stop talking about airflow created by the prop. It isn't part of the question.

So we have facts (A) and (B) well taken care of. If the plane moves, it flies. If it doesn't move, it doesn't fly. The real question is, will it move? Again, the answer is unambiguous - if the pilot doesn't try to make the plane stay still, it won't. If he does, it will. This is always, always the part that confuses people, so stick with me for a few more paragraphs.

When a plane is sitting on a runway, it moves by using its engines. It does not move by any sort of motorized wheel. The propellers or jets create thrust that pushes against the surrounding air and causes the plane to move forward. A plane wouldn't move at all in a vacuum chamber. Compare this to a car, which moves by applying torque to the wheels. A car would drive just fine in a vacuum chamber - at least, as long as the driver could survive (and technically, it would need some sort of air reservoir to provide something to mix with the fuel. An electric car wouldn't have this problem.) However, a car could not drive on a frictionless surface - imagine, for example, that you had your car on a super slippery frozen lake. As you hit the gas, the wheels would simply spin and spin in place, and the car wouldn't move forward. You may even have firsthand experience with this situation if you've ever gotten stuck in a snow bank. In contrast, a plane would have no trouble moving on a frictionless surface. The jet engines or propeller would still push against the air, and the plane would still move forward. If it were on a truly frictionless surface, then you would see the wheels sliding along the ground, not rotating.

I hope those two scenarios clearly illustrate the difference in motive force between cars and planes. Cars create their forward movement from torque applied to the wheels, which push against the ground and create forward motion from friction. Planes create their forward movement from thrust applied to the air, which pushes the plane forward regardless of the surface it is on.

Imagine a plane without wheels. The fuselage would sit on the runway, and as you fired up the engines, it would skid spectacularly along the runway, possibly spewing sparks in its wake and doing quite a number on the body of the aircraft. No matter how fast it was going, the frictional force against the airplane would be constant; friction does not depend on speed! If the engines were strong enough to get the plane up to the critical take-off speed, then it would still take off. The only reason planes have wheels is to reduce this sliding friction. The wheels roll along the runway instead of sliding, and the only friction that the plane feels is in the bearings of the wheels. This is substantially less than the friction that a sliding fuselage would create, and it's a much smoother ride for the passengers as well.

(Edit: Technically, there are some factors that would make the friction change with speed. The classic idealized model called "coulomb friction" doesn't really apply to bearings. As the bearings spun faster and faster, they would generate heat, which would increase the friction slightly on the wheels. However, it would never be enough force to prevent take-off. The only time this would prevent take-off is if the wheels locked up or broke off, and then we'd have a much bigger problem and catastrophic failure.)

So what does this all have to do with treadmills? Well, now let's place our plane on that treadmill and see what happens. If the wheels were perfect - that is, there is no friction in the bearings (and no deformation of the wheels as they spin) - then something interesting happens. When we turn on the treadmill, the plane stays stationary on its own. The wheels simply spin along the track, and impart no force to the plane. If you had a car with frictionless axles, and you disconnected the whole drive train, the same thing would happen to your car.

The only reason that a plane or a car moves backwards on a treadmill is that the wheels are somehow partially locked to the axles. In a plane, this is because of minor friction in the bearings. In a car, it's because of the drive train. If you want the car to stay still, you have to turn the drive train at the proper speed. If you want the plane to stay still, you have to overcome the minor bearing friction. And again, since friction does not change with speed, you don't have to exert any more force at higher speeds. If you run the treadmill at 5mph and turn on the plane's engines just slightly, they will provide enough thrust, pushing against the air, to keep the plane still. If you then increase the treadmill speed to 500 mph, you won't need to adjust the throttle on the airplane - it will remain stationary. That's because it's seeing the same frictional force that it was at 5mph. Thus, it doesn't matter how fast the treadmill is moving - if the pilot does not want to remain stationary, then he won't. It only uses the very first bit of power from the engines to keep the plane stationary. As the throttle is increased from that point, it moves forward just as it would on any other runway. It's pushing against the stationary air!

If you don't believe me, imagine this (or even try it at home): you're standing on a skateboard on a treadmill. You hold onto the handrails of the treadmill and turn it on. Of course, you'll remain stationary (relative to the ground). In fact, you only need to use a very light touch to stay stationary - perhaps a few fingers pressed against the handrails. Crank up the treadmill speed as high as you like. You'll still only need the same light touch to remain stationary. At any time you like, you can move forward - closer to the treadmill console - by simple pulling on the handrails. If you had a jet engine, or super-strong hairdryer, you could use this to propel yourself forward instead of holding onto the handrails. In fact, if you're really careful, you might be able to do this at home with a skateboard and a leafbower, but I doubt you'll have a sensitive enough control of your leafblower thrust to get yourself to remain stationary.

So you see (oh please tell me you see), the conveyor operator cannot force the plane to remain stationary. And if the plane isn't stationary, it can take off.

And yes, if we interpret the question in a different way, and assume that for some reason the pilot is colluding with the conveyor operator and keeping the plane stationary, then the plane can't take off.

But what is the question really getting at, anyway? There are really two "spirits" of the question. In the first, we're asking "can a plane take off with no runway, if I replace the runway with a treadmill?" The answer, as we know now, is no. The plane must move relative to the ground in order to take off. In another deep-meaning of the question, we're asking "is it possible to prevent a plane from taking off, by moving the runway backwards under it?" The answer again is no, you can't prevent it from taking off.

The interesting thing about all this is that in both scenarios, you'd wind up with a plane moving relative to the ground. In the first scenario, you might think you're being clever by allowing a plane to take off from a very small field, by using a treadmill runway. If you actually tried it, you'd be attempting to take off, so the plane would move, and would likely crash into something, or fall off a cliff, or suffer some other catastrophe that you were trying to avoid with questionable physics. In the second scenario, you'd give the plane plenty of room and safety to take off, but attempt to play a practical joke on the pilot by moving the runway backwards, and you'd wind up with a plane in flight, much to your chagrin.

When the "no-flys" saw the Mythbusters episode, they all complained that it wasn't done properly, because the plane didn't remain stationary. But think about it for a moment. No, really think about it, don't just spout about Bernoulli's principle and airflow and all that. In what possible scenario would the plane actually stay still? The only way this can happen is if the pilot is trying to stay still, and this only happens if he just barely applies the throttle, making no attempt to take off. This makes no sense. Either you're trying to prevent him from taking off with your clever and misinformed use of a conveyor belt, or he's trying to defy physics by taking off in a too-small area. There is no scenario in which the plane would realistically stay still. We know what would happen if it did - it would sit on the runway, not taking off, and we'd all stare at each other in an all-too-short silence punctuated by loud exclamations of "I told you so!". But that's not really what the thought experiment is getting at, no matter how you reasonably interpret it. Luckily for all of us, if we agree on the interpretation, reasonable or not, we should all agree on the answer.

So let's get back to the next great internet debate, shall we?

I don't have anything to say, I just enjoy making people scroll unnecessarily "

That's just unnecessary.

Reply privatelyReply in forumReply +quote
 

By *enard ArgenteMan
over a year ago

London and France

if a plane crashes exactly on the US / Canada border, where do you bury the survivors?

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk


"if a plane crashes exactly on the US / Canada border, where do you bury the survivors?

"

I would very much hope you wouldn't bury survivors

Reply privatelyReply in forumReply +quote
 

By (user no longer on site)
over a year ago

Not read everything.... but in my view you need airspeed (airflow under wings) for pressure to lift, thus airborne.

Reply privatelyReply in forumReply +quote
 

By *unandbuckCouple
over a year ago

Sheffield

Thanks Dee Viant I have posted on Pt3 similar (thanks to your link)

This is a word puzzle, not a physics puzzle.

If the belt tracks the planes speed, then both things have speed.

If the plane has speed it flies.

It is intended to trick by how it is phrased.

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk


"Not read everything.... but in my view you need airspeed (airflow under wings) for pressure to lift, thus airborne.

"

Nobody is disputing that.

If you think the 'plane won't move wrt to the ground, you need to read the article.

The belt CANNOT hold the 'plane still in relation to the ground by itself, regardless of its speed.

Unless the pilot of the 'plane acts with the belt in order to hold the 'plane stationary in relation to the ground, the 'plane will be driven forward by the engines.

Reply privatelyReply in forumReply +quote
 

By (user no longer on site)
over a year ago

Yes the planes wheels will be going round.. if the pilot hits the brakes then the plane will be thrust forwards... is this what your trying to ask?

Reply privatelyReply in forumReply +quote
 

By *unandbuckCouple
over a year ago

Sheffield

Aaaaaaahhhh !!

Its a word puzzle !

The question says ' the belt matches the planes speed'

For the belt to have speed the plane must have speed.

If the plane has speed it flies.

Reply privatelyReply in forumReply +quote
 

By (user no longer on site)
over a year ago


"Aaaaaaahhhh !!

Its a word puzzle !

The question says ' the belt matches the planes speed'

For the belt to have speed the plane must have speed.

If the plane has speed it flies."

No it doesn't.. it needs airflow to get airborne

Reply privatelyReply in forumReply +quote
 

By *unandbuckCouple
over a year ago

Sheffield


"Aaaaaaahhhh !!

Its a word puzzle !

The question says ' the belt matches the planes speed'

For the belt to have speed the plane must have speed.

If the plane has speed it flies.

No it doesn't.. it needs airflow to get airborne "

This thread is on Part 3, with 400+ posts. You are saying what lots of people have said.

It is a trick question.

Read through the threads

Reply privatelyReply in forumReply +quote
 

By (user no longer on site)
over a year ago

Fuck reading that lot all over again! Haha

I'm going to get a treadmill and borrow a light aircraft from a friend...

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk


"Aaaaaaahhhh !!

Its a word puzzle !

The question says ' the belt matches the planes speed'

For the belt to have speed the plane must have speed.

If the plane has speed it flies.

No it doesn't.. it needs airflow to get airborne "

Please read the post.

Or at least take the argument back to the physics thread.

The conveyor belt cannot, by itself, stop the 'plane moving forward.

There are a few different ways in which this question can be considered but it is a fact, that by itself, the conveyor cannot hold the 'plane still in relation to the ground.

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk


"Fuck reading that lot all over again! Haha

I'm going to get a treadmill and borrow a light aircraft from a friend... "

Just read the first post on this thread.

Reply privatelyReply in forumReply +quote
 

By (user no longer on site)
over a year ago

Most boring thread of 2016. Off to watch paint dry

Reply privatelyReply in forumReply +quote
 

By *unandbuckCouple
over a year ago

Sheffield


"Most boring thread of 2016. Off to watch paint dry"

'Threads' - Pt3 is going. 400 posts cant be wrong....

Reply privatelyReply in forumReply +quote
 

By *enard ArgenteMan
over a year ago

London and France


"if a plane crashes exactly on the US / Canada border, where do you bury the survivors?

I would very much hope you wouldn't bury survivors "

Exactly; but I asked this question once in a management seminar, and the argument raged for an hour; even after I had stopped them after half an hour and ecplained that you don't bury survivors; they continued to obsess about the legal issues of location and jurisdiction, despite there being an illogical question.

The point was to prove that to solve a problem; you have to make sure you know what the problem is; and that decisions are made in business, politics ( dare I say elections?) when an answer is given,without checking what the question/problem actuality is.

And in my my role leading an organisation which carried out analysis of situations for other organisations; we would be asked to solve a problem or asked a question; the first 25% of effort was to analyse the question ; often ( actually always) going back to the customer to refine the question; or tell them that they were actually asking the wrong question

Reply privatelyReply in forumReply +quote
 

By (user no longer on site)
over a year ago

Are you all still bickering about this?

Your never all gonna agree

Reply privatelyReply in forumReply +quote
 

By *unandbuckCouple
over a year ago

Sheffield


"if a plane crashes exactly on the US / Canada border, where do you bury the survivors?

I would very much hope you wouldn't bury survivors

Exactly; but I asked this question once in a management seminar, and the argument raged for an hour; even after I had stopped them after half an hour and ecplained that you don't bury survivors; they continued to obsess about the legal issues of location and jurisdiction, despite there being an illogical question.

The point was to prove that to solve a problem; you have to make sure you know what the problem is; and that decisions are made in business, politics ( dare I say elections?) when an answer is given,without checking what the question/problem actuality is.

And in my my role leading an organisation which carried out analysis of situations for other organisations; we would be asked to solve a problem or asked a question; the first 25% of effort was to analyse the question ; often ( actually always) going back to the customer to refine the question; or tell them that they were actually asking the wrong question "

Just what we do on here , on lots of threads.

Instead, take a step back, think.

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk


"Are you all still bickering about this?

Your never all gonna agree "

I've posted the flipping answer, from two separate sources, 4 times so far and yes, they're still bickering!

Reply privatelyReply in forumReply +quote
 

By *unandbuckCouple
over a year ago

Sheffield


"Are you all still bickering about this?

Your never all gonna agree

I've posted the flipping answer, from two separate sources, 4 times so far and yes, they're still bickering! "

More to learn from that fact, than about the answer to the original question, I think.

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk


"Are you all still bickering about this?

Your never all gonna agree

I've posted the flipping answer, from two separate sources, 4 times so far and yes, they're still bickering!

More to learn from that fact, than about the answer to the original question, I think."

As a psychology experiment it's absolutely fascinating

Reply privatelyReply in forumReply +quote
 

By *adyDangerWoman
over a year ago

land of debauchery and kink

Any need for all that quoting, never scrolled so much in my life. Total waste of server space.

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk


"Any need for all that quoting, never scrolled so much in my life. Total waste of server space. "

I'm not allowed to post the link, so yes.

Reply privatelyReply in forumReply +quote
 

By (user no longer on site)
over a year ago


"Are you all still bickering about this?

Your never all gonna agree

I've posted the flipping answer, from two separate sources, 4 times so far and yes, they're still bickering! "

I'm staying out of it..It's just fun to watch

Reply privatelyReply in forumReply +quote
 

By *adyDangerWoman
over a year ago

land of debauchery and kink


"Any need for all that quoting, never scrolled so much in my life. Total waste of server space.

I'm not allowed to post the link, so yes."

Not you I meant the person who quoted what you wrote 4 times to be a smart arse

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk


"Are you all still bickering about this?

Your never all gonna agree

I've posted the flipping answer, from two separate sources, 4 times so far and yes, they're still bickering!

I'm staying out of it..It's just fun to watch "

It is that.

I tried to be helpful though, for those who actually want to know.

The rest are more bothered about being right than finding out what the actual answer is!

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk


"Any need for all that quoting, never scrolled so much in my life. Total waste of server space.

I'm not allowed to post the link, so yes.

Not you I meant the person who quoted what you wrote 4 times to be a smart arse "

Yes, that was a bit pointless. It takes all sorts...

Reply privatelyReply in forumReply +quote
 

By (user no longer on site)
over a year ago


"Are you all still bickering about this?

Your never all gonna agree

I've posted the flipping answer, from two separate sources, 4 times so far and yes, they're still bickering!

I'm staying out of it..It's just fun to watch

It is that.

I tried to be helpful though, for those who actually want to know.

The rest are more bothered about being right than finding out what the actual answer is!"

I'm gonna come back at some point and read and attempt to understand it..just for my own interest. It does rather seem to be a better psychology experiment than a physics one though at the moment I don't know where I fall as I've not read it and tried to understand it. I sometimes need to sit and think or stuff to get in my brain..I'm a bit slow on the uptake at times. (especially if I'm on a treadmill)

Reply privatelyReply in forumReply +quote
 

By *xx1Man
over a year ago

.

Without airflow it'll be impossible to take off.

So, no!..... But, with cake, now that's a different story, as anything is possible with "cake!" X

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk


"Are you all still bickering about this?

Your never all gonna agree

I've posted the flipping answer, from two separate sources, 4 times so far and yes, they're still bickering!

I'm staying out of it..It's just fun to watch

It is that.

I tried to be helpful though, for those who actually want to know.

The rest are more bothered about being right than finding out what the actual answer is!

I'm gonna come back at some point and read and attempt to understand it..just for my own interest. It does rather seem to be a better psychology experiment than a physics one though at the moment I don't know where I fall as I've not read it and tried to understand it. I sometimes need to sit and think or stuff to get in my brain..I'm a bit slow on the uptake at times. (especially if I'm on a treadmill) "

Ask me for the links. The articles are laid out better on their own pages and a bit easier to follow.

The XKCD one has diagrams.

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk


"Without airflow it'll be impossible to take off.

So, no!..... But, with cake, now that's a different story, as anything is possible with "cake!" X "

Your first statement is correct.

The "no" isn't.

Go read the flippin' article!

The physics thread is the one for the arguing. This is the one for people who actually want a decent explaination of the question and are willing to think about it!

Reply privatelyReply in forumReply +quote
 

By (user no longer on site)
over a year ago


"Are you all still bickering about this?

Your never all gonna agree

I've posted the flipping answer, from two separate sources, 4 times so far and yes, they're still bickering!

I'm staying out of it..It's just fun to watch

It is that.

I tried to be helpful though, for those who actually want to know.

The rest are more bothered about being right than finding out what the actual answer is!

I'm gonna come back at some point and read and attempt to understand it..just for my own interest. It does rather seem to be a better psychology experiment than a physics one though at the moment I don't know where I fall as I've not read it and tried to understand it. I sometimes need to sit and think or stuff to get in my brain..I'm a bit slow on the uptake at times. (especially if I'm on a treadmill)

Ask me for the links. The articles are laid out better on their own pages and a bit easier to follow.

The XKCD one has diagrams."

pictures..now we're talking!

i'll come hastle you for them in a bit. headed out shortly but it might make for an interesting read later

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk


"Are you all still bickering about this?

Your never all gonna agree

I've posted the flipping answer, from two separate sources, 4 times so far and yes, they're still bickering!

I'm staying out of it..It's just fun to watch

It is that.

I tried to be helpful though, for those who actually want to know.

The rest are more bothered about being right than finding out what the actual answer is!

I'm gonna come back at some point and read and attempt to understand it..just for my own interest. It does rather seem to be a better psychology experiment than a physics one though at the moment I don't know where I fall as I've not read it and tried to understand it. I sometimes need to sit and think or stuff to get in my brain..I'm a bit slow on the uptake at times. (especially if I'm on a treadmill)

Ask me for the links. The articles are laid out better on their own pages and a bit easier to follow.

The XKCD one has diagrams.

pictures..now we're talking!

i'll come hastle you for them in a bit. headed out shortly but it might make for an interesting read later "

The problem with the question is that it can be interpreted in more than one way, and one of the apparent possibilities is actually impossible.

It's a really bad question which is part of the reason for the extent of the arguments.

One group take the question one way, and think the answer is obvious and another group take the question a different way and think a different answer is obvious and both groups think the other group is dim and tries to explain basic physics to them.

It's great!

Reply privatelyReply in forumReply +quote
 

By *enard ArgenteMan
over a year ago

London and France

Perhaps we should try to find out if a helicopter can take off if it is sat on a turntable which rotates at the same speed ( but in the opposite direction) as the rotor.

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk


"Perhaps we should try to find out if a helicopter can take off if it is sat on a turntable which rotates at the same speed ( but in the opposite direction) as the rotor.

"

Perhaps we shouldn't!

Reply privatelyReply in forumReply +quote
 

By (user no longer on site)
over a year ago

What does the PiTot read? If no R.A.F. There's lift, no lift no fly.

Reply privatelyReply in forumReply +quote
 

By *horltzMan
over a year ago

heysham


"Copied from a link I can't share. For the love of all things horny, read it until you understand it!

I created this blog specifically to make this post. It may be the only post I ever write, but since human ignorance is seemingly unbounded, perhaps it won't be.

I thought that today would be a monumental day for this topic. Today, the Mythbusters debuted their long-awaited "Airplane on a treadmill" episode. For years, physics teachers around the world have cringed in horror at heated internet debates concerning a ludicrous thought experiment. Sadly, half of them recoiled in disgust at the correct arguments. Forum posters signed their names with such epithets as "Ph.D. Aerospace Engineer" and "20-year pilot." Somewhat tellingly, these ego-boosters were most often employed by those delivering the wrong answers. Mythbusters finally attempted to end the insanity by performing the experiment themselves.

AND YET...

The debate rages on. Even after being shown seemingly conclusive evidence of the other side's argument, forum-goers from near and far continued to staunchly defend their own theories.

Here and now, the debate will end. I intend this long-winded article to be the definitive answer to the great AOAT conundrum. No further debate is necessary - simply direct the ignorant people to this page, tell them to read it, and let's all get on with answering more intriguing questions, like does P = NP?

For those of you just joining us, "Airplane On A Treadmill," also known as "Airplane on a Conveyor Belt," is a thought experiment in physics. Some consider it a litmus test for assessing one's knowledge of airplane physics. In its most basic form, the experiment is worded thusly:

A plane is standing on a large treadmill or conveyor belt. The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the plane speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction). Can the plane take off?

The question suffers from many rewordings that muddle much of the debate about the thought experiment. The basic idea is that there's a plane, on a treadmill, and we're going to run the treadmill backwards in an attempt to stop the plane from taking off. And here, at the very beginning of this explanation, is the definitive answer. There are in fact two correct answers to this question:

- No, the plane can't take off.

- Yes, the plane can take off.

Fooled you! But that's just the point. The experiment is meaningless, and the passionate internet debates more so, if we cannot agree on what is truly meant by the question. But don't worry, I won't pull a Lost on you - I do intend to give a truly airtight answer later on. For now though, we need to debate semantics.

Really, we do.

You see, the AOAT confusion all arises from misses - misconceptions, misinterpretations, and misunderstandings. Consider three rewordings of the question:

1) An airplane is sitting at rest on a very powerful treadmill. You are at the controls of the treadmill, while I am at the controls of the airplane. On some signal, I begin to attempt to take flight in the plane, and you attempt to match my speed to try to keep me stationary. Will the plane take off?

2) An airplane is sitting at rest on a very powerful treadmill. You are at the controls of the treadmill, while I am at the controls of the airplane. On some signal, I throttle up the airplane and you turn on the treadmill, and we conspire by our joint effort to try to keep the plane stationary relative to the ground. Will the plane take off?

3) An airplane is sitting at rest on a very powerful treadmill. You are at the controls of the treadmill, while I am at the controls of the airplane. On some signal, I attempt to take flight in the plane, but you match my speed with the treadmill and keep me stationary relative to the ground. Will the plane take off?

Here are the absolute, 100%, bet-your-life-on-it answers to these rewordings:

Yes.

No.

Whoever asked this question is an idiot.

And that's about all this debate comes down to, folks. If we could all agree on one set of rules for the thought experiment, then we ought to be able to make the explanation of the answer clear. As it stands, normally one side has interpretation (1) in mind, and argues vehemently with someone else who has interpretation (2) in mind, and the whole thing blows up into a senseless squabble.

Here are the three core facts that are rock-solid:

A) If the plane remains stationary relative to the ground, it will not take off.

B) If the plane moves relative to the ground, it will take off.

C) The person operating the conveyor belt CANNOT by himself make the plane remain stationary relative to the ground.

(EDIT: Really, you should substitute the word "air" for ground in the above facts. I use "ground" throughout this post because of a consistent mistake made by "no-flys" in their assumption that the plane remains stationary. It doesn't remain stationary, relative to the ground or the air. The important point is that it moves relative to the air, not the ground, but I'm assuming throughout this post that there is no significant tailwind or headwind. I discuss the implications of this briefly in the section about windtunnels.)

That's about all you need to know to argue whichever interpretation is appropriate. I'll discuss why these facts are true in a moment. In the meantime, look back at the three re-wordings of the question above.

In (1), the key phrase is "you attempt to match my speed to try to keep me stationary." Since we know from fact (C) that you cannot keep me stationary, it follows from (B) that I will take off successfully.

In (2), we conspire together to keep the plane stationary. This is possible, albeit stupid. We know from fact (A) that I will not take off.

In (3) - and this is the important part - the actions being described are impossible. We know from (C) that the conveyor operator cannot keep the plane stationary. The most powerful conveyor belt in the world couldn't do it. David Copperfield couldn't do it. It can't be done. Only if the pilot "plays along" can the plane be made to remain stationary.

Unfortunately, most of the "no-flys" - the label given to those who argue that the plane won't take off - are assuming that interpretation (3) is what is being asked. They accept that the plane remains stationary, and say it won't take off. The "will-flys" know that the plane can't remain stationary, and say it will take off. Add to the mix a few people who see that in one way, the plane could be forced to be stationary by some pilot-conveyor cooperation, and you've got a deadly internet forum explosion cocktail.

Let's examine the physics behind the three key facts, so that there will be no doubt as to their validity. The first two are pretty easy to follow. Airplanes create lift by causing air to flow over their wings. This airflow is caused by the motion of the wings relative to the air - that can happen in two ways. The first way is to move the plane forward through the air. The second is to blow air against the plane and over the wings. As far as the plane is concerned, these two scenarios are equivalent. So you could put a plane in a very powerful wind tunnel, blow air over its wings, and have it fly stationary relative to the ground. But that's another question.

In our treadmill scenario, the air is stationary relative to the ground, so the plane has to move relative to the ground in order to gain flight. If it doesn't move, it simply won't fly. There will be no airflow over the wings, and there will be no lift. A lot of people get confused here, and think that the original thought experiment is some sort of trick question, and that the propeller of the airplane, or possibly the jet engines, will be blowing air backwards over the wings, which will create lift. While there will be a certain amount of airflow created by the propeller or engines, it is not enough to create flight. I promise you, that's not what the question is asking.

Really, I promise. Please, please stop talking about airflow created by the prop. It isn't part of the question.

So we have facts (A) and (B) well taken care of. If the plane moves, it flies. If it doesn't move, it doesn't fly. The real question is, will it move? Again, the answer is unambiguous - if the pilot doesn't try to make the plane stay still, it won't. If he does, it will. This is always, always the part that confuses people, so stick with me for a few more paragraphs.

When a plane is sitting on a runway, it moves by using its engines. It does not move by any sort of motorized wheel. The propellers or jets create thrust that pushes against the surrounding air and causes the plane to move forward. A plane wouldn't move at all in a vacuum chamber. Compare this to a car, which moves by applying torque to the wheels. A car would drive just fine in a vacuum chamber - at least, as long as the driver could survive (and technically, it would need some sort of air reservoir to provide something to mix with the fuel. An electric car wouldn't have this problem.) However, a car could not drive on a frictionless surface - imagine, for example, that you had your car on a super slippery frozen lake. As you hit the gas, the wheels would simply spin and spin in place, and the car wouldn't move forward. You may even have firsthand experience with this situation if you've ever gotten stuck in a snow bank. In contrast, a plane would have no trouble moving on a frictionless surface. The jet engines or propeller would still push against the air, and the plane would still move forward. If it were on a truly frictionless surface, then you would see the wheels sliding along the ground, not rotating.

I hope those two scenarios clearly illustrate the difference in motive force between cars and planes. Cars create their forward movement from torque applied to the wheels, which push against the ground and create forward motion from friction. Planes create their forward movement from thrust applied to the air, which pushes the plane forward regardless of the surface it is on.

Imagine a plane without wheels. The fuselage would sit on the runway, and as you fired up the engines, it would skid spectacularly along the runway, possibly spewing sparks in its wake and doing quite a number on the body of the aircraft. No matter how fast it was going, the frictional force against the airplane would be constant; friction does not depend on speed! If the engines were strong enough to get the plane up to the critical take-off speed, then it would still take off. The only reason planes have wheels is to reduce this sliding friction. The wheels roll along the runway instead of sliding, and the only friction that the plane feels is in the bearings of the wheels. This is substantially less than the friction that a sliding fuselage would create, and it's a much smoother ride for the passengers as well.

(Edit: Technically, there are some factors that would make the friction change with speed. The classic idealized model called "coulomb friction" doesn't really apply to bearings. As the bearings spun faster and faster, they would generate heat, which would increase the friction slightly on the wheels. However, it would never be enough force to prevent take-off. The only time this would prevent take-off is if the wheels locked up or broke off, and then we'd have a much bigger problem and catastrophic failure.)

So what does this all have to do with treadmills? Well, now let's place our plane on that treadmill and see what happens. If the wheels were perfect - that is, there is no friction in the bearings (and no deformation of the wheels as they spin) - then something interesting happens. When we turn on the treadmill, the plane stays stationary on its own. The wheels simply spin along the track, and impart no force to the plane. If you had a car with frictionless axles, and you disconnected the whole drive train, the same thing would happen to your car.

The only reason that a plane or a car moves backwards on a treadmill is that the wheels are somehow partially locked to the axles. In a plane, this is because of minor friction in the bearings. In a car, it's because of the drive train. If you want the car to stay still, you have to turn the drive train at the proper speed. If you want the plane to stay still, you have to overcome the minor bearing friction. And again, since friction does not change with speed, you don't have to exert any more force at higher speeds. If you run the treadmill at 5mph and turn on the plane's engines just slightly, they will provide enough thrust, pushing against the air, to keep the plane still. If you then increase the treadmill speed to 500 mph, you won't need to adjust the throttle on the airplane - it will remain stationary. That's because it's seeing the same frictional force that it was at 5mph. Thus, it doesn't matter how fast the treadmill is moving - if the pilot does not want to remain stationary, then he won't. It only uses the very first bit of power from the engines to keep the plane stationary. As the throttle is increased from that point, it moves forward just as it would on any other runway. It's pushing against the stationary air!

If you don't believe me, imagine this (or even try it at home): you're standing on a skateboard on a treadmill. You hold onto the handrails of the treadmill and turn it on. Of course, you'll remain stationary (relative to the ground). In fact, you only need to use a very light touch to stay stationary - perhaps a few fingers pressed against the handrails. Crank up the treadmill speed as high as you like. You'll still only need the same light touch to remain stationary. At any time you like, you can move forward - closer to the treadmill console - by simple pulling on the handrails. If you had a jet engine, or super-strong hairdryer, you could use this to propel yourself forward instead of holding onto the handrails. In fact, if you're really careful, you might be able to do this at home with a skateboard and a leafbower, but I doubt you'll have a sensitive enough control of your leafblower thrust to get yourself to remain stationary.

So you see (oh please tell me you see), the conveyor operator cannot force the plane to remain stationary. And if the plane isn't stationary, it can take off.

And yes, if we interpret the question in a different way, and assume that for some reason the pilot is colluding with the conveyor operator and keeping the plane stationary, then the plane can't take off.

But what is the question really getting at, anyway? There are really two "spirits" of the question. In the first, we're asking "can a plane take off with no runway, if I replace the runway with a treadmill?" The answer, as we know now, is no. The plane must move relative to the ground in order to take off. In another deep-meaning of the question, we're asking "is it possible to prevent a plane from taking off, by moving the runway backwards under it?" The answer again is no, you can't prevent it from taking off.

The interesting thing about all this is that in both scenarios, you'd wind up with a plane moving relative to the ground. In the first scenario, you might think you're being clever by allowing a plane to take off from a very small field, by using a treadmill runway. If you actually tried it, you'd be attempting to take off, so the plane would move, and would likely crash into something, or fall off a cliff, or suffer some other catastrophe that you were trying to avoid with questionable physics. In the second scenario, you'd give the plane plenty of room and safety to take off, but attempt to play a practical joke on the pilot by moving the runway backwards, and you'd wind up with a plane in flight, much to your chagrin.

When the "no-flys" saw the Mythbusters episode, they all complained that it wasn't done properly, because the plane didn't remain stationary. But think about it for a moment. No, really think about it, don't just spout about Bernoulli's principle and airflow and all that. In what possible scenario would the plane actually stay still? The only way this can happen is if the pilot is trying to stay still, and this only happens if he just barely applies the throttle, making no attempt to take off. This makes no sense. Either you're trying to prevent him from taking off with your clever and misinformed use of a conveyor belt, or he's trying to defy physics by taking off in a too-small area. There is no scenario in which the plane would realistically stay still. We know what would happen if it did - it would sit on the runway, not taking off, and we'd all stare at each other in an all-too-short silence punctuated by loud exclamations of "I told you so!". But that's not really what the thought experiment is getting at, no matter how you reasonably interpret it. Luckily for all of us, if we agree on the interpretation, reasonable or not, we should all agree on the answer.

So let's get back to the next great internet debate, shall we?

I don't have anything to say, I just enjoy making people scroll unnecessarily

That's just unnecessary."

And childish

Reply privatelyReply in forumReply +quote
 

By *enard ArgenteMan
over a year ago

London and France


"What does the PiTot read? If no R.A.F. There's lift, no lift no fly."

We are dealing with the fly and the électrocuter on a different thread.

I think we have decided the fly died and doesn't revive

Reply privatelyReply in forumReply +quote
 

By (user no longer on site)
over a year ago

I lost interest after about 2 paragraphs as it proves most totally misunderstand basic physics and principles of flight.

Reply privatelyReply in forumReply +quote
 

By *unandbuckCouple
over a year ago

Sheffield


"I lost interest after about 2 paragraphs as it proves most totally misunderstand basic physics and principles of flight."

Aah might be worth reading then, as you might find you were 'wrong' too

Reply privatelyReply in forumReply +quote
 

By *eesideMan
over a year ago

margate sumwear by the sea

Just wotched the myth busters clip. Plain on a tredmoll. ok I wos rong I wos not expecting that...... To anyone hoo thinks it won't take off wotch this clip.

The plan dus take off

Carnt argue with the evidence.

Reply privatelyReply in forumReply +quote
 

By *xx1Man
over a year ago

.


"Without airflow it'll be impossible to take off.

So, no!..... But, with cake, now that's a different story, as anything is possible with "cake!" X

Your first statement is correct.

The "no" isn't.

Go read the flippin' article!

The physics thread is the one for the arguing. This is the one for people who actually want a decent explaination of the question and are willing to think about it!"

Who care.... I've got cake x

Reply privatelyReply in forumReply +quote
 

By (user no longer on site)
over a year ago

Does this qualify for longest post ever?

Reply privatelyReply in forumReply +quote
 

By *aucy tiggerWoman
over a year ago

Back where I belong

I'm just glad I'm not on the plane or the treadmill xx

Reply privatelyReply in forumReply +quote
 

By *omez42Man
over a year ago

gloucester

As soon as the CAA sort out my medical...

I'm going flying

Reply privatelyReply in forumReply +quote
 

By (user no longer on site)
over a year ago

I couldn't face reading it all but I do have a question- will the air steward be coming round on this plane soon with drinks? I need vodka

Reply privatelyReply in forumReply +quote
 

By *ralbiswMan
over a year ago

Exeter


"I'm more worried that this is gonna descend into 'Physics....vol' 4' "

We are about 70 posts from volume 4!!! I don't want to go there!

Reply privatelyReply in forumReply +quote
 

By (user no longer on site)
over a year ago

Ahh so it's a trick question? I'll try it for real this weekend

Reply privatelyReply in forumReply +quote
 

By (user no longer on site)
over a year ago


"PS the 'plane DOES move except when the pilot colludes to stop it. Please read the article again until you understand why."

I read the original article....about 20 yrs back.

Wether you or others re-worded it (apologies if I got this wrong...it wasn't you). The re-wordings were all done to try and twist the scenario in some way to try to justify their wrong result.

The original "thought experiment" has the plane stationary.

However if the plane us stationary relative to the ground then it IS also stationary relative to the air so no uplift...no take off.

The initial thought experiment simply had a frictionless conveyor so that it automatically revolved backwards at whatever speed the wheels rotated.

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk


"PS the 'plane DOES move except when the pilot colludes to stop it. Please read the article again until you understand why.

I read the original article....about 20 yrs back.

Wether you or others re-worded it (apologies if I got this wrong...it wasn't you). The re-wordings were all done to try and twist the scenario in some way to try to justify their wrong result.

The original "thought experiment" has the plane stationary.

However if the plane us stationary relative to the ground then it IS also stationary relative to the air so no uplift...no take off.

The initial thought experiment simply had a frictionless conveyor so that it automatically revolved backwards at whatever speed the wheels rotated."

I don't know about the original thought experiment, what we're all discussing is the one that was posted on here. The article above is relevant to that.

I'm not sure of the point of bringing yet another scenario into it.

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk

Unless, of course, it's bringing yet another scenario into it in order to justify a wrong answer...

Reply privatelyReply in forumReply +quote
 

By *riskynriskyCouple
over a year ago

Essex.

Is Schrodinger's cat in the hold???

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk


"Is Schrodinger's cat in the hold??? "

Could well be!

Reply privatelyReply in forumReply +quote
 

By *riskynriskyCouple
over a year ago

Essex.

The trouble is, we can't look...

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk


"The trouble is, we can't look... "

Lord Lucan and Shergar could be in there too.

Reply privatelyReply in forumReply +quote
 

By *riskynriskyCouple
over a year ago

Essex.


"The trouble is, we can't look...

Lord Lucan and Shergar could be in there too."

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk


"The trouble is, we can't look...

Lord Lucan and Shergar could be in there too. "

I wonder if the extra weight would be a factor in whether it can take off.

Reply privatelyReply in forumReply +quote
 

By *riskynriskyCouple
over a year ago

Essex.


"The trouble is, we can't look...

Lord Lucan and Shergar could be in there too.

I wonder if the extra weight would be a factor in whether it can take off."

The extra horse power might help...

Reply privatelyReply in forumReply +quote
 

By *harpDressed ManMan
over a year ago

Here occasionally, but mostly somewhere else


"Longest post of the year winner.

#notsuitableifyouhaveshortattentionspan.

I did do a tl;dr"

You could have flagged it's existence at the start!!

Reply privatelyReply in forumReply +quote
 

By *ee Viante OP   Woman
over a year ago

Somewhere in North Norfolk


"Longest post of the year winner.

#notsuitableifyouhaveshortattentionspan.

I did do a tl;dr

You could have flagged it's existence at the start!!"

I didn't know it would exist at the start! It was an afterthought.

Reply privatelyReply in forumReply +quote
 

By *unandbuckCouple
over a year ago

Sheffield


"The trouble is, we can't look...

Lord Lucan and Shergar could be in there too.

I wonder if the extra weight would be a factor in whether it can take off."

No, they are on a mini helicopter in the hold, so the plane wouldn't weigh any extra.......

Reply privatelyReply in forumReply +quote
 

By *harpDressed ManMan
over a year ago

Here occasionally, but mostly somewhere else


"No, they are on a mini helicopter in the hold, so the plane wouldn't weigh any extra....... "

That's just silly.

No helicopter with a racehorse on it could be called "mini"

Reply privatelyReply in forumReply +quote
 

By *unandbuckCouple
over a year ago

Sheffield


"No, they are on a mini helicopter in the hold, so the plane wouldn't weigh any extra.......

That's just silly.

No helicopter with a racehorse on it could be called "mini"

"

BMW made it and call it and called it 'mini' . It can fit 3 horses and still room for schroedingers cat in the boot.

Reply privatelyReply in forumReply +quote
 

By *harpDressed ManMan
over a year ago

Here occasionally, but mostly somewhere else


"BMW made it and call it and called it 'mini' . It can fit 3 horses and still room for schroedingers cat in the boot."

BMW don't make helicopters, so their first attempt would be unlikely to be a new standard in miniaturisation.

You must think I was born yesterday...

Reply privatelyReply in forumReply +quote
 

By *unandbuckCouple
over a year ago

Sheffield


"BMW made it and call it and called it 'mini' . It can fit 3 horses and still room for schroedingers cat in the boot.

BMW don't make helicopters, so their first attempt would be unlikely to be a new standard in miniaturisation.

You must think I was born yesterday..."

They have some history in making aeroplanes....

Reply privatelyReply in forumReply +quote
 

By *harpDressed ManMan
over a year ago

Here occasionally, but mostly somewhere else


"BMW made it and call it and called it 'mini' . It can fit 3 horses and still room for schroedingers cat in the boot.

BMW don't make helicopters, so their first attempt would be unlikely to be a new standard in miniaturisation.

You must think I was born yesterday...

They have some history in making aeroplanes...."

Did they make them unusually small?

Reply privatelyReply in forumReply +quote
 

By *enard ArgenteMan
over a year ago

London and France


"BMW made it and call it and called it 'mini' . It can fit 3 horses and still room for schroedingers cat in the boot.

BMW don't make helicopters, so their first attempt would be unlikely to be a new standard in miniaturisation.

You must think I was born yesterday...

They have some history in making aeroplanes....

Did they make them unusually small?"

BMW ( Bayerische Motoren Werke) was originally a manufacturer of aircraft engines. Founded in 1916. The BMW logo represents a spinning propeller.

One if it's predecessor companies was Bayerische Flugzeuge Werke; ( Bavarian Aircraft Works) which was an aircraft manufacturer.

Reply privatelyReply in forumReply +quote
 

By *harpDressed ManMan
over a year ago

Here occasionally, but mostly somewhere else

Don't bring facts to this nonsense!

Reply privatelyReply in forumReply +quote
 

By *unandbuckCouple
over a year ago

Sheffield


"

They have some history in making aeroplanes....

Did they make them unusually small?

BMW ( Bayerische Motoren Werke) was originally a manufacturer of aircraft engines. Founded in 1916. The BMW logo represents a spinning propeller.

One if it's predecessor companies was Bayerische Flugzeuge Werke; ( Bavarian Aircraft Works) which was an aircraft manufacturer.

"

Correct. They were also the first to develop a rotating belt platform to allow vertical takeoff of stationary fixed wing aircraft...

Reply privatelyReply in forumReply +quote
 

By *harpDressed ManMan
over a year ago

Here occasionally, but mostly somewhere else

That's better, I feel safe again now!

Reply privatelyReply in forumReply +quote
 

By (user no longer on site)
over a year ago

Ads has been debating this elsewhere and to be honest it all makes my head hurt... I got half way through reading it in the hope I could dazzle him with facts but sadly it just made me realise I have a short attention span when it comes to all things science!

G x

Reply privatelyReply in forumReply +quote
 
 

By (user no longer on site)
over a year ago


"

...

When a plane is sitting on a runway, it moves by using its engines. It does not move by any sort of motorized wheel. The propellers or jets create thrust that pushes against the surrounding air and causes the plane to move forward. A plane wouldn't move at all in a vacuum chamber. Compare this to a car, which moves by applying torque to the wheels. A car would drive just fine in a vacuum chamber - at least, as long as the driver could survive (and technically, it would need some sort of air reservoir to provide something to mix with the fuel. An electric car wouldn't have this problem.) However, a car could not drive on a frictionless surface - imagine, for example, that you had your car on a super slippery frozen lake. As you hit the gas, the wheels would simply spin and spin in place, and the car wouldn't move forward. You may even have firsthand experience with this situation if you've ever gotten stuck in a snow bank. In contrast, a plane would have no trouble moving on a frictionless surface. The jet engines or propeller would still push against the air, and the plane would still move forward. If it were on a truly frictionless surface, then you would see the wheels sliding along the ground, not rotating.

...

Planes create their forward movement from thrust applied to the air, which pushes the plane forward regardless of the surface it is on.

...

"

Now that we seem to have cracked the main problem, I am suprised that no one has picked up on this...

The propellors and jet engines don't provide thrust by pushing on the air.

They provide thrust by Newton's Third Law, often quoted as "for every action there is an equal and opposite reaction".

Both propellors and jet engines take air and thow it backwards at high speed. This creates the equal force forwards acting on the plane providing thrust. Just like rockets in space where, naturally, there is no air to push on.

The reason a plane wouldn't move in a vacuum chamber is because it has no air for the propellor or jet to throw out behind it, not because there is no air to push on. If you gave it a supply, as in a rocket, it would work very well.

Reply privatelyReply in forumReply +quote
Post new Message to Thread
back to top