Mythbusters punk'd whole internet

[LTC8K6]

"Nobody was debating that the plane doesn't take off."

Huh?

 

[Dean]

There are people still arguing this? Holy!!

The plane thrust only has to account for the low additional wheel rotational friction, it still moves forward and will take off. No matter how fast the treadmill moves, the planes forward speed will mean it's wheels are going that much faster than the treadmill. The plane is essentially being pushed forward by it's own air thrust.

I'm bored of this one.

Lets try this. You have a helicopter in a giant vacuumed enclosure, will it be able to lift and hover? LOL

 

[RapidSnail]

Originally posted by: LTC8K6
"Nobody was debating that the plane doesn't take off."

Huh?

*Sigh*

 

[Leros]

Originally posted by: Dean
There are people still arguing this? Holy!!

The plane thrust only has to account for the low additional wheel rotational friction, it still moves forward and will take off. No matter how fast the treadmill moves, the planes forward speed will mean it's wheels are going that much faster than the treadmill. The plane is essentially being pushed forward by it's own air thrust.

I'm bored of this one.

Lets try this. You have a helicopter in a giant vacuumed enclosure, will it be able to lift and hover? LOL

No. That stupid.

What was the answer to the helicopter on a rotation platform that matched the speed of the rotor blades? It seems pretty obvious that the answer is no since the blades don't move relative to the air. But I could be wrong.

 

[StevenYoo]

plane takes off

 

[mugs]

Originally posted by: RapidSnail

Originally posted by: RapidSnail
Simple solution:

If the speed of the treadmill matches the speed of the wheels, the plane can not take off.

If the speed of the treadmill matches the speed of the plane, the plan can take off.

Originally posted by: spidey07
And in order for it to move forward the wheels have to go faster than the treadmill.

This is NOT allowed. If it is then the treadmill is not matching the speed of the wheels.

You're using the first scenario, aren't you?

The first scenario cannot exist.

In order for the treadmill to move, the plane must move relative to the ground. The wheels of a stationary plane do not roll. Thus the plane will have to start moving along the treadmill in order for the wheels to start rolling. As soon as the wheels start rolling the requirements of the problem have been broken - the wheels are moving faster than the treadmill. The treadmill can't move until the wheels move, and as soon as the wheels move the requirements are broken. It's a problem that describes a scenario that cannot exist.

Thus it is not even worth discussing scenario 1. There is no possible answer to scenario 1.

 

[smack Down]

Originally posted by: mugs

Originally posted by: LTC8K6
"Its OBVIOUS the plane will NOT take off."

What is keeping it from taking off?

MasonLuke is a troll, ignore him. IIRC, he has been banned in the past because of his posts in a thread on this topic. You're not going to get anywhere with him. Logic, reason and physics will get you nowhere.

Don't bother with most of these people... if they don't get it after two or three explanations, they're not ever going to accept reality. Take smack down for instance - he knows the outcome of on Mythbusters is not going to match his opinion, so he tried to discredit it before the show even started.

There are plenty of very valid analogies that you can test yourself - the suitcase on a moving walkway is a good one. Rollerblades + rope on a treadmill is an excellent analogy. If people close their mind to reality, you won't get anywhere with them.

Sorry but your analogys are hopeless bad. First of all you are minimizing the mass of the wheels when you should be maximizing it. Second you are missing the most important aspect of the system a treadmill that matches the speed of the object.

 

[Fenixgoon]

Originally posted by: smack Down

Originally posted by: mugs

Originally posted by: LTC8K6
"Its OBVIOUS the plane will NOT take off."

What is keeping it from taking off?

MasonLuke is a troll, ignore him. IIRC, he has been banned in the past because of his posts in a thread on this topic. You're not going to get anywhere with him. Logic, reason and physics will get you nowhere.

Don't bother with most of these people... if they don't get it after two or three explanations, they're not ever going to accept reality. Take smack down for instance - he knows the outcome of on Mythbusters is not going to match his opinion, so he tried to discredit it before the show even started.

There are plenty of very valid analogies that you can test yourself - the suitcase on a moving walkway is a good one. Rollerblades + rope on a treadmill is an excellent analogy. If people close their mind to reality, you won't get anywhere with them.

Sorry but your analogys are hopeless bad. First of all you are minimizing the mass of the wheels when you should be maximizing it. Second you are missing the most important aspect of the system a treadmill that matches the speed of the object.

and you ignore the fact that the wheels freely rotate. hence, treadmill speed does not matter. the plane will take off regardless of the treadmill speed.

 

[smack Down]

Originally posted by: mugs

Originally posted by: Fenixgoon

Originally posted by: mugs

Originally posted by: LTC8K6
"Its OBVIOUS the plane will NOT take off."

What is keeping it from taking off?

MasonLuke is a troll, ignore him. IIRC, he has been banned in the past because of his posts in a thread on this topic. You're not going to get anywhere with him. Logic, reason and physics will get you nowhere.

Don't bother with most of these people... if they don't get it after two or three explanations, they're not ever going to accept reality. Take smack down for instance - he knows the outcome of on Mythbusters is not going to match his opinion, so he tried to discredit it before the show even started.

There are plenty of very valid analogies that you can test yourself - the suitcase on a moving walkway is a good one. Rollerblades + rope on a treadmill is an excellent analogy. If people close their mind to reality, you won't get anywhere with them.

what's the suitcase one? don't think i've heard that.

LTC8K6 posted it about 15 posts up.

I posted another one that you can't really duplicate yourself. Put a car on a treadmill with only the free-spinning wheels on a treadmill. That treadmill can spin all it wants, it's not going to prevent the driving wheels from pulling/pushing the car off the treadmill. The driving wheels are equivalent to the jet engines of the airplane - their force is NOT applied to the treadmill. The free-spinning wheels are equivalent to the free-spinning wheels on a plane. The treadmill can spin those wheels all it wants, but the minimal friction is not going to hold the car back or the plane back.

Spidey is right that the plane would move backward on the treadmill if the engines were not on. That's because there is friction in the wheels. But it is not nearly enough to hold the plane back.

It isn't friction that cause the plane to roll back. And it is very easy to prove put a wheel on the treadmill with no axle and it to will move backwards. The size of the force doesn't mater if the treadmill can control it by increasing its speed.

 

[Leros]

Say the plane is trying to move 100mph down the treadmill. Because the mass of the wheels are so small, the treadmill will have to be flying back at millions of miles per hour in order to counteract the plane's speed and mass (made up number, but the the point is the treadmill will have to be going really freaking fast). But assuming you could do that in real life, the plane would not take off since the treadmill would essentially hold the plane in place.

I'm not expert on planes, but my understanding is that the lift of the plane comes from the wings cutting through the air. All the engines do is push the plane forward. If this super fast treadmill is holding the plane in place, there will be no lift.

 

[RapidSnail]

Originally posted by: mugs

Originally posted by: RapidSnail

Originally posted by: RapidSnail
Simple solution:

If the speed of the treadmill matches the speed of the wheels, the plane can not take off.

If the speed of the treadmill matches the speed of the plane, the plan can take off.

Originally posted by: spidey07
And in order for it to move forward the wheels have to go faster than the treadmill.

This is NOT allowed. If it is then the treadmill is not matching the speed of the wheels.

You're using the first scenario, aren't you?

The first scenario cannot exist.

In order for the treadmill to move, the plane must move relative to the ground. The wheels of a stationary plane do not roll. Thus the plane will have to start moving along the treadmill in order for the wheels to start rolling. As soon as the wheels start rolling the requirements of the problem have been broken - the wheels are moving faster than the treadmill. The treadmill can't move until the wheels move, and as soon as the wheels move the requirements are broken. It's a problem that describes a scenario that cannot exist.

Thus it is not even worth discussing scenario 1. There is no possible answer to scenario 1.

The first scenario can exist if the plane is tethered to some point and the wheel speed is arbitrarily defined, thus causing the treadmill to match it. The engine is not the source of power, instead definition; and the plane does not move. It's more hypothetical than anything. The way I described the scenario was vague, so I can understand why you are confused.

 

[NanoStuff]

Originally posted by: Leros
Say the plane is trying to move 100mph down the treadmill. Because the mass of the wheels are so small, the treadmill will have to be flying back at millions of miles per hour

I don't know which side exactly you were arguing for before, there's probably at least 5 sides here, but it's probable that you betrayed a side that was closer to the truth than where you are now. You're going backwards, much like the plane.

 

[jagec]

Originally posted by: Leros
Say the plane is trying to move 100mph down the treadmill. Because the mass of the wheels are so small, the treadmill will have to be flying back at millions of miles per hour in order to counteract the plane's speed and mass (made up number, but the the point is the treadmill will have to be going really freaking fast). But assuming you could do that in real life, the plane would not take off since the treadmill would essentially hold the plane in place.

I'm not expert on planes, but my understanding is that the lift of the plane comes from the wings cutting through the air. All the engines do is push the plane forward. If this super fast treadmill is holding the plane in place, there will be no lift.

Actually, it has to be ACCELERATING. Speed alone does nothing. There is no way to hold the plane back in steady-state...if the plane has an infinite reservoir of fuel, the treadmill would have to be continuously accelerating backwards to infinity.

I did the calculations. To counteract the thrust of an average jet (100,000 kg, 1,000kN combined thrust, 14 tires @ 1.2m diameter, 200kg each), the treadmill has to continously accelerate backwards at 714 m/s^2.

Interestingly enough, this is actually higher than frictional forces between the wheel and the treadmill can support. If we decrease the thrust of the plane to 880kN (which is reasonable, a 777 has thrust varying from 660 to 1020kN max depending on engines), the no-slip condition is once again reestablished, and the treadmill must accelerate backwards at 630 m/s^2. Friction in the wheel hubs will bring this number down slightly.

Ridiculously high, certainly. But non-relativistic.

Originally posted by: mugs

In order for the treadmill to move, the plane must move relative to the ground. The wheels of a stationary plane do not roll. Thus the plane will have to start moving along the treadmill in order for the wheels to start rolling. As soon as the wheels start rolling the requirements of the problem have been broken - the wheels are moving faster than the treadmill. The treadmill can't move until the wheels move, and as soon as the wheels move the requirements are broken. It's a problem that describes a scenario that cannot exist.

So if you turn on the cold water in a room that's temperature controlled at 70 degrees, thus breaking the requirements of the problem, the world explodes?

Before you say "that's an invalid analogy", consider...by imparting an additional heat flux into the room via the furnace, the control system can make up for the cold water flow. By imparting an additional acceleration on the treadmill (speed doesn't do anything), the control system can make up for engine thrust.

This is a difficult problem because there is no way to draw a steady-state solution that keeps the plane on the runway. You have to have the time factor, since acceleration but not speed affects the plane.

It's much like the momentum wheels/reaction wheels which are used to point satellites...they do NOTHING at speed, but an acceleration (change of speed) is able to affect the satellite

 

[mobobuff]

spidey07 is having a laugh. He's smarter than this.

I think after the last plane-on-a-treadmill thread, all the smarter posters got together in some secret lair and agreed that when the next POAT thread came up, they would all jump the fence and argue the other side just to confuse bitches. It would've been a hilarious idea and frankly I'm sad that I wasn't invited.

spidey07 is ignoring the original intent of the question as it was originally and simplistically stated so that he can push the plane not taking off. In his scenario the plane CAN take off, but not without breaking the rules of the problem (belt speed = wheel speed). That is not, however, the correct interpretation of the problem. I can't say I was the first to think of this question and that I have the authority to say what it implies, but I think it's obvious how it's supposed to be interpreted, as spidey07's interpretation is a paradox and a useless question. His point about the plane moving backwards when no thrust is applied is weak and pointless. The thrust from the plane will easily overcome the friction of the wheel axles. To put it differently, if the belt went from 0 to 500mph instantly with no thrust from the plane, the plane would remain almost stationary as the friction would be removed from the instant introduction of fast motion.

I swear he's sitting back and laughing right now.

 

[MasonLuke]

Originally posted by: mugs

Originally posted by: LTC8K6
"Its OBVIOUS the plane will NOT take off."

What is keeping it from taking off?

MasonLuke is a troll, ignore him. IIRC, he has been banned in the past because of his posts in a thread on this topic. You're not going to get anywhere with him. Logic, reason and physics will get you nowhere.

Don't bother with most of these people... if they don't get it after two or three explanations, they're not ever going to accept reality. Take smack down for instance - he knows the outcome of on Mythbusters is not going to match his opinion, so he tried to discredit it before the show even started.

There are plenty of very valid analogies that you can test yourself - the suitcase on a moving walkway is a good one. Rollerblades + rope on a treadmill is an excellent analogy. If people close their mind to reality, you won't get anywhere with them.

Mugs, you are the troll. I can express my opinion on this matter just as you have. Leave me alone and get a life. I thank you in advance.

 

[jagec]

Originally posted by: mobobuff
spidey07 is ignoring the original intent of the question as it was originally and simplistically stated so that he can push the plane not taking off. In his scenario the plane CAN take off, but not without breaking the rules of the problem (belt speed = wheel speed). That is not, however, the correct interpretation of the problem. I can't say I was the first to think of this question and that I have the authority to say what it implies, but I think it's obvious how it's supposed to be interpreted, as spidey07's interpretation is a paradox and a useless question. His point about the plane moving backwards when no thrust is applied is weak and pointless. The thrust from the plane will easily overcome the friction of the wheel axles. To put it differently, if the belt went from 0 to 500mph instantly with no thrust from the plane, the plane would remain almost stationary as the friction would be removed from the instant introduction of fast motion.

I swear he's sitting back and laughing right now.

"You keep using that word. I do not think it means what you think it means."

Built-in to your assumptions is that there is NO way for the threadmill to affect the plane speed, which makes the paradox argument fallacious. If the treadmill is able to reduce the speed of the plane to zero (with respect to a stationary object), the control scenario of wheel speed=treadmill speed is maintained. Yes, there will be an initial violation as the plane starts moving, but all control systems are like that. Typical control system response curve. If I set my cruise control to 70, and when I start going up a hill and it drops to 68 before recovering and speeding back up to 70, I don't claim that the control condition has been violated and my cruise control is not working.

But we do need a way for the treadmill to affect the plane's speed, and that method is through angular momentum. If we can put a force on the wheels equal to the force the engines are exerting on a plane, we will have a force couple, which leads to a torque and no net linear force. The AOAT is special, however, since the wheels can turn in response to these forces. With massless wheels this would mean that we are physically incapable of exerting an equal force to oppose the engines, since as we attempt to exert more force, the wheels just spin faster. However, there is a resistance to that torque, which is angular momentum. Thus, as long as we can accelerate the wheels quickly enough to maintain a constant force equal and opposite to that created by the engines, we can hold the plane in place.

Here's an example of linear-angular interaction.
A satellite in space has a momentum wheel currently turning at velocity V. The satellite is stationary. Suddenly a system malfunctions, and a low-power thruster on the perimeter of the satellite begins to fire with force Fl. Now, (a)by applying a force Ft to the momentum wheel, can the satellite maintain its orientation? (b)can the satellite prevent a linear translation?

(a) is "yes", (b)is "no".

/edited for clarity, fixed links.

 

[spidey07]

Originally posted by: mobobuff
spidey07 is having a laugh. He's smarter than this.

I think after the last plane-on-a-treadmill thread, all the smarter posters got together in some secret lair and agreed that when the next POAT thread came up, they would all jump the fence and argue the other side just to confuse bitches. It would've been a hilarious idea and frankly I'm sad that I wasn't invited.

spidey07 is ignoring the original intent of the question as it was originally and simplistically stated so that he can push the plane not taking off. In his scenario the plane CAN take off, but not without breaking the rules of the problem (belt speed = wheel speed). That is not, however, the correct interpretation of the problem. I can't say I was the first to think of this question and that I have the authority to say what it implies, but I think it's obvious how it's supposed to be interpreted, as spidey07's interpretation is a paradox and a useless question. His point about the plane moving backwards when no thrust is applied is weak and pointless. The thrust from the plane will easily overcome the friction of the wheel axles. To put it differently, if the belt went from 0 to 500mph instantly with no thrust from the plane, the plane would remain almost stationary as the friction would be removed from the instant introduction of fast motion.

I swear he's sitting back and laughing right now.

Not really dude. I'm just trying to stay within bounds. Conceptually such a thing can't exist, mathematically it can. But you're right, it's a paradox.

My point about no thrust is to point out those that continually believe there is a disconnect between the plane and treadmill is false. Realistically and mathematically you can retard the advancement of the plane.

 

[Skeeedunt]

:laugh:

Alright, well this thread still going, so I have a question:

Originally posted by: jagec

Originally posted by: Skeeedunt
I think this finally makes sense. If the wheels are frictionless, the plane takes of. Otherwise, the conveyor can move the wheels so fast that the downward force of the wheels' rotational inertia is so great that it counteracts the thrust of the engine against the air. Am I right am I right?? Do I get a cookie??

Change "downward" to "backwards", friction actually isn't necessary (but it certainly lowers the treadmill requirements), but besides that :thumbsup:. Note that this is only for the second definition of the control system...in the first definition the plane will take off every time.

I never actually understood why the force applied by linear momentum was backwards any more than it was, say, forward or upward. Is it simply a fact that the linear momentum would be in the opposite direction of a force applied at a wheel's edge (i.e. the treadmill)?

 

[JoeKing]

Take a hot wheel toy car, put it on a treadmill, turn on the treadmill, and while still holding the car push it forward on the treadmill (opposite direction treadmill is running). Does the car still move forward? Yes. So with the airplane your arm would represent the thrust from the props, jets, little fuzzy hamster.

 

[Fritzo]

Originally posted by: Darwin333

Originally posted by: Fritzo
I don't understand the debate on this in the first place---if a plane is on a conveyor belt, only the belt and the wheels on the plane would be moving. It's the compression of air underneath the wings that causes flight---since the conveyor belt is not forcing the air around the wings, the plane would not be able to take off. If the conveyor had some kind of paddles attached to it to move air, it could cause enough lift, or if there were a huge fan in front of the plane it could cause lift, but moving wheels under a plane will do nothing.

Is there some other aspect of this I'm missing?

Yes. The thrust produced from the jet engines.

The thrust from the engines would be pushing the plane foward. If it's on a conveyor, there still would be no air moving over and under the wings. You see?

 

[mobobuff]

Originally posted by: spidey07

Originally posted by: mobobuff
spidey07 is having a laugh. He's smarter than this.

I think after the last plane-on-a-treadmill thread, all the smarter posters got together in some secret lair and agreed that when the next POAT thread came up, they would all jump the fence and argue the other side just to confuse bitches. It would've been a hilarious idea and frankly I'm sad that I wasn't invited.

spidey07 is ignoring the original intent of the question as it was originally and simplistically stated so that he can push the plane not taking off. In his scenario the plane CAN take off, but not without breaking the rules of the problem (belt speed = wheel speed). That is not, however, the correct interpretation of the problem. I can't say I was the first to think of this question and that I have the authority to say what it implies, but I think it's obvious how it's supposed to be interpreted, as spidey07's interpretation is a paradox and a useless question. His point about the plane moving backwards when no thrust is applied is weak and pointless. The thrust from the plane will easily overcome the friction of the wheel axles. To put it differently, if the belt went from 0 to 500mph instantly with no thrust from the plane, the plane would remain almost stationary as the friction would be removed from the instant introduction of fast motion.

I swear he's sitting back and laughing right now.

Not really dude. I'm just trying to stay within bounds. Conceptually such a thing can't exist, mathematically it can. But you're right, it's a paradox.

My point about no thrust is to point out those that continually believe there is a disconnect between the plane and treadmill is false. Realistically and mathematically you can retard the advancement of the plane.

You're not staying within ANY bounds. You're submitting arguments which do not ultimately imply that the plane will NOT take off, you're pointing out the technical minutiae in the relationship between the conveyor and plane. Saying "Yes, the plane does take off" is a very simple and easy conclusion, but it is also the correct one. Yes there is a small and insignificant relationship between the belt and the plane, the wheels do not rule that out and we know that. However, in the original boundaries of the question, the belt and plane will only be moving at 150-200mph (if we assume there is no wind) by the time the plane achieves the required airspeed and takes off. Arguing anything beyond that point is arguing a different question altogether.

 

[randay]

Originally posted by: Fritzo

Originally posted by: Darwin333

Originally posted by: Fritzo
I don't understand the debate on this in the first place---if a plane is on a conveyor belt, only the belt and the wheels on the plane would be moving. It's the compression of air underneath the wings that causes flight---since the conveyor belt is not forcing the air around the wings, the plane would not be able to take off. If the conveyor had some kind of paddles attached to it to move air, it could cause enough lift, or if there were a huge fan in front of the plane it could cause lift, but moving wheels under a plane will do nothing.

Is there some other aspect of this I'm missing?

Yes. The thrust produced from the jet engines.

The thrust from the engines would be pushing the plane foward. If it's on a conveyor, there still would be no air moving over and under the wings. You see?

ROFL

 

[dainthomas]

Originally posted by: Fritzo

Originally posted by: Darwin333

Originally posted by: Fritzo
I don't understand the debate on this in the first place---if a plane is on a conveyor belt, only the belt and the wheels on the plane would be moving. It's the compression of air underneath the wings that causes flight---since the conveyor belt is not forcing the air around the wings, the plane would not be able to take off. If the conveyor had some kind of paddles attached to it to move air, it could cause enough lift, or if there were a huge fan in front of the plane it could cause lift, but moving wheels under a plane will do nothing.

Is there some other aspect of this I'm missing?

Yes. The thrust produced from the jet engines.

The thrust from the engines would be pushing the plane foward. If it's on a conveyor, there still would be no air moving over and under the wings. You see?

 

[Exterous]

Originally posted by: Leros

Originally posted by: Dean
There are people still arguing this? Holy!!

The plane thrust only has to account for the low additional wheel rotational friction, it still moves forward and will take off. No matter how fast the treadmill moves, the planes forward speed will mean it's wheels are going that much faster than the treadmill. The plane is essentially being pushed forward by it's own air thrust.

I'm bored of this one.

Lets try this. You have a helicopter in a giant vacuumed enclosure, will it be able to lift and hover? LOL

No. That stupid.

What was the answer to the helicopter on a rotation platform that matched the speed of the rotor blades? It seems pretty obvious that the answer is no since the blades don't move relative to the air. But I could be wrong.

It wouldn't. With no air to beat into submission a helicopter cannot fly.

From how long and hotly debated these threads are I don't think mythbusters will be able to put this to rest. Whatever they find there will be critics on their methods either way.


God help us all if their testing is inconclusive!

 

[mrSHEiK124]

Originally posted by: waggy

Originally posted by: smack Down

If the plane is going backwards then it would mean that the treadmill is no longer matching the wheel speed of the plane. The treadmill would have to be going faster then the wheels. Stop think of the plane as something special just think of it like a car.

thats the problem. THIS IS NOTHING LIKE A CAR.

really its not. a car gets its thrust by the wheels. a plane by the thrust of the engines.

For every action, there is an equal and opposite reaction. the thrust of the engine has to have its opposite action. the wheels/treadmill ARE NOT IT.

Thank you, best explanation ever.

THE AIRPLANE TAKES OFF. The wheels moving backwards, forwards, sideways; fuck, take off the wheels and make the damn plane slide across the treadmill, IT WILL TAKE OFF. None of the forces I just mentioned would do ANYTHING to counter the thrust of the jet engines. NOTHING.