Mythbusters punk'd whole internet

[FoBoT]

i just meant whether the treadmill changes speed or stays at a constant speed

 

[randay]

got trolled again, game over.

 

[jagec]

Originally posted by: FoBoT
nobody said the treadmill has a magic speed sensing control system. i don't remember anything like that in the original thingy
but is doesn't matter anyway, see yoyojelloman's bag analogy above ^^^

"magic"? Did the guy who installed the cruise control on your car have to put on his robe and wizard hat first?

From the original problem:

?Imagine a plane is sitting on a massive conveyor belt, as wide and as long as a runway. The conveyer belt is designed to exactly match the speed of the wheels, moving in the opposite direction. Can the plane take off? ?

But first you need to realize that I agree with the bag analogy above, and the case that I and a few others are arguing is the second interpretation of the problem, which is slightly more complex. I have stated this in several of my previous posts in this very thread.

Originally posted by: randay

Oh I see, you're smack down? He goes with the same torque/angular momental arguement and he also makes up the same convenient "control system".

Untrue. Smack down's "conversion" to angular momentum only occurred after he realized that his argument was unsound, and so he tried to borrow mine but screwed up on the details. I don't think he understands the principles of my argument at all.

Look, it's not hard to understand. There MUST be a control system for this problem to work at all. There are two ways to program this control system, depending on how you interpret the initial problem:
First (most reasonable, easiest to understand, and probably correct):
A stationary sensor measures the speed of the plane, and feeds that number directly into the treadmill, which runs in reverse. Net result: The plane rolls down the runway and takes off easily, with the wheels spinning more quickly than normal.

Second (interesting thought experiment, but people are getting hung up on semantics):
The speed of the treadmill is controlled via a speed sensor in the wheels, which attempts to equalize the speed of the wheels with that of the treadmill, but in the opposite direction. A mathematically identical, but conceptually easier scenario is a position sensor on the plane, and a control system on the treadmill which attempts to keep the plane fixed in position by adjusting treadmill speed and acceleration.

Now, IF the treadmill has no way to change the position of the plane, the control system will just continuously accelerate to try and match the wheels, until it burns out and/or reaches infinity.

HOWEVER, the plane and the treadmill are coupled via two terms: Frictional forces in the wheel hub, and angular momentum of the wheels. As such, if the treadmill accelerates quickly, it can actually build up a linear force at the wheel hub. If it accelerates fast enough, it can actually match the force provided by the engines, and the plane remains stationary. Given the small mass of the wheels and the low frictional forces, this requires fairly ludicrous amounts of acceleration, and as such a real-world treadmill could not use this effect to stop a plane from taking off. But if you allow boundless acceleration, you will find that the treadmill is capable of holding the plane at a standstill until its fuel reserves are exhausted, at which point the amount of angular momentum tied up in the wheels is twice the energy content of the fuel, after you subtract engine inefficiencies and frictional losses. The treadmill (and the wheels) will be moving at an extreme, but non-relativistic, rate of speed.


/edit: Dammit, I am NOT trolling you. Smack down might have been, I'm not sure. By all means poke holes in my arguments, send me nasty PMs, whatever, and if you can prove me wrong DO so. But don't discard my argument as without merit until you have fully understood it!

 

[YOyoYOhowsDAjello]

I'm really interested to hear which way Mythbusters chooses (or chose rather) to interpret the problem and whether or not they're going to address the fact that these two interpretations of the problem lead to different (but perfectly logical) conclusions.

 

[randay]

You are taking the conclusion that the airplanes forward movement can be equalized by the treadmill and changing the scenario so that it happens. basically changing the question compeltely. I dont see the point in debating any of it.

either the treadmill tracks the air speed of the plane, or it tracks the speed of the planes wheel on itself. In which case it accelerates to infinity. it CANNOT increase earths gravity, cut the airplanes fuel lines, or take away the pilots license. And it certainly cannot choose to ignore the wheelspeed paradox and only accelerate enough to keep the airplanes airspeed at exactly 0.

 

[Dean]

Take a dinky and place it on a moving treadmill and push it forward, you will still move it forward and all it will take is a small amount of extra force to account for the added wheel friction. A plane would behave in the same manner, the forward momentum from the propeller will "push" the plane forward and the planes wheels will always be faster than the treadmill no matter how fast the treadmill is going. All it will take is more thrust to overcome the wheel friction.

 

[zinfamous]

Originally posted by: waggy

Originally posted by: NanoStuff

Originally posted by: waggy
good diragram that shows what i mean


you guys are getting hung up on wheel speed and convyer belt speed. it really does not matter.

the wheels do not provide any power. all power comes from the engines. no matter what the plane is going ot go foreword. foreword motion is going to provide lift. so the plane takes off.

You're not about to understand this even if I tried my damn best trying to explain it, but it doesn't make a difference. If the wheels are tractionally bound to the ground, the plane's forward speed is directly proportional to the rotation of the wheels. If the conveyor belt compensates for the wheels, the plain goes nowhere, much like with a car. They have conveyor belts for testing cars, the cars don't take off, trust me.

wow..

there is a huge diffrence between a CAR and a plane. you put a car on the traedmill yes it wont take off. why? ITS A FUCKING CAR. the power is generated by the wheels.

With a plane its in the engines that produce thrust. with thrust the foreword mementom has nothing to do with the wheels. so you can ignore them. its going to move.

the 3rd law proves that..

look, these people don't understand the difference between a car's AXLES, which transfer force via the engine and through its wheels, and a plane's free-spinning wheels, which are IN NO WAY providing force through the plane's engines.

Even if you shoved their faces under a car to point out how car wheels interact with the engine, and the very simple principles of how they work, and do the same with the wheels on a plane, they will still continue to believe that car wheels = plane wheels.

they're idiots.

give up on them, as they will not evolve with the rest of us

 

[Fenixgoon]

i would just like to say that the plane will take off, regardless of the treadmill, as long as it achieves sufficient thrust

the plane's thrust is not dependent on its tires (unlike a car, where torque is applied through the wheels to the ground). the tires are there simply to reduce friction. you could take the wheels off the plane and it'd still take off.

 

[Auric]

Originally posted by: mobobuff

Originally posted by: RapidSnail
Is there something I'm missing here? It's obvious after some logical thought that the plane will take off if the conditions are that the treadmill must match the speed of the airplane's thrusters. Was there another version of the question that has people confused for some reason? The only way the plane couldn't take of is if the treadmill matches the rotational speed of the wheels instead of the thrusters, but other than that there is no argument.

That's pretty much it. The plane takes off in the original sense of the problem, but arguing that has gotten boring. Now the idea is to create a scenario where the plane DOESN'T take off.

Lest we forget that ground contact is only relevant in so much as it can retard air passing the wings front to back and thus prevent sufficient lift. Given 'nuff wind, a plane can "take off without moving" regardless of wheels but the only way to create its own lift from stationary is to achieve a certain ground speed. It doesn't really matter how that is thwarted if the goal is to prevent flight. A theoretical treadmill will do but so what? Seems like mental masturbation for dullards.

 

[jagec]

Originally posted by: YOyoYOhowsDAjello
I'm really interested to hear which way Mythbusters chooses (or chose rather) to interpret the problem and whether or not they're going to address the fact that these two interpretations of the problem lead to different (but perfectly logical) conclusions.

On the one hand I'd like to see that, but on the other hand this thread is bad enough, so maybe it would be better for society if they just stuck to the first, easy interpretation.

Originally posted by: randay
You are taking the conclusion that the airplanes forward movement can be equalized by the treadmill and changing the scenario so that it happens. basically changing the question compeltely. I dont see the point in debating any of it.

either the treadmill tracks the air speed of the plane, or it tracks the speed of the planes wheel on itself. In which case it accelerates to infinity. it CANNOT increase earths gravity, cut the airplanes fuel lines, or take away the pilots license. And it certainly cannot choose to ignore the wheelspeed paradox and only accelerate enough to keep the airplanes airspeed at exactly 0.

#1. I disagree with this premise. Like I said, treadmill acceleration can be used to KEEP the airplane stationary on the treadmill, with the wheels continuously accelerating as well to soak up the force being channeled into them by the engines and the accelerating treadmill. Once the airplane is stationary, wheel speed=treadmill speed...no paradox.

I don't understand the second bolded portion. Once the airplane is stationary (airspeed=0), there is no reason why the treadmill should accelerate above that threshold. In that case, wheel speed = treadmill speed, which is the design in the first place. Now, if we had specified that the treadmill must always be going FASTER than the wheels, then I agree, it would need to accelerate continuously and lead to a paradox. As it stands, it just leads to a very fast-moving treadmill.

Here's an example that might make some sense.

Let's say you have a house in the middle of winter. There is a furnace capable of generating as much heat as you like, and a control system that's trying to keep the house at a constant 70 degrees. Now you reroute the furnace to across the street and open the door. At first glance this looks like it will lead to a paradox, because the furnace is not directly linked to the house and as such cannot keep it warm. The control system turns up the furnace more and more, and the house temperature continues to drop. However, as the control system turns the furnace up more and more, eventually a second-order effect rises to prominence: The entire neighborhood is getting heated to 70+ degrees, and eventually all that warm air from outside comes into the house and warms it up, thus satisfying the control condition.

 

[Rastus]

I want to know when they are going to tackle the 10 lbs. of bulk beef question.

 

[YOyoYOhowsDAjello]

Originally posted by: Rastus
I want to know when they are going to tackle the 10 lbs. of bulk beef question.

The "can you shoot 10 lbs. of bulk beef out of a canon into a dead pig dressed up like a pirate" question?

 

[lizardboy]

Originally posted by: Rastus
I want to know when they are going to tackle the 10 lbs. of bulk beef question.

Where can I buy beef in bulk? I'm thinking about 10 pounds.

 

[randay]

Originally posted by: YOyoYOhowsDAjello

Originally posted by: Rastus
I want to know when they are going to tackle the 10 lbs. of bulk beef question.

The "can you shoot 10 lbs. of bulk beef out of a canon into a dead pig dressed up like a pirate" question?

Can we replace this car alternator with 10 pounds of beef? Find out next week on MYTHBUSTERS!

 

[Sphexi]

There's an episode online now that has airplane in the title, can I assume it's a fake?

 

[mobobuff]

Originally posted by: Sphexi
There's an episode online now that has airplane in the title, can I assume it's a fake?

You can assume it's lame and doesn't talk about POAC.

 

[dug777]

Originally posted by: mobobuff

Originally posted by: Sphexi
There's an episode online now that has airplane in the title, can I assume it's a fake?

You can assume it's lame and doesn't talk about POAC.

Who cares?

We know it won't take off.

 

[YOyoYOhowsDAjello]

Originally posted by: dug777

Originally posted by: mobobuff

Originally posted by: Sphexi
There's an episode online now that has airplane in the title, can I assume it's a fake?

You can assume it's lame and doesn't talk about POAC.

Who cares?

We know it won't take off.

In the southern hemisphere, the treadmill takes off.

 

[dug777]

Originally posted by: YOyoYOhowsDAjello

Originally posted by: dug777

Originally posted by: mobobuff

Originally posted by: Sphexi
There's an episode online now that has airplane in the title, can I assume it's a fake?

You can assume it's lame and doesn't talk about POAC.

Who cares?

We know it won't take off.

In the southern hemisphere, the treadmill takes off.

Only if you forget to nail it down properly.

Planes taking off here isn't the problem, it's keeping them on the ground that occupies our finest minds.

 

[YOyoYOhowsDAjello]

Originally posted by: dug777

Originally posted by: YOyoYOhowsDAjello

Originally posted by: dug777

Originally posted by: mobobuff

Originally posted by: Sphexi
There's an episode online now that has airplane in the title, can I assume it's a fake?

You can assume it's lame and doesn't talk about POAC.

Who cares?

We know it won't take off.

In the southern hemisphere, the treadmill takes off.

Only if you forget to nail it down properly.

Planes taking off here isn't the problem, it's keeping them on the ground that occupies our finest minds.

How do submarines work down there?

 

[gorcorps]

*serious post*

Good lord I can't believe this is still being debated. It was a bit tough to think of at first but after hearing a good explanation of it from my physics prof it made perfect sense.

The plane will take off normally. Anybody who thinks otherwise is confusing how a plane takes off with how a car moves. A car moves by propelling itself with friction: the tire sticks to the ground and the wheels turn, and because the tires have friction with the ground the turning wheels make the car move. A plane moves by forcing air behind it, the wheels are just there for stability and takeoff/landing. If a treadmill was under the wheels of the plane moving backwards, then the air from the jets/propeller will move the plane at normal speed, the wheels will just be turning twice as fast (the speed of the plane+the speed of the treadmill which matches the plane). From looking at just the plane as a whole it will take off normally, but looking at the wheels they're spinning twice as fast as they normally would.

From a physics point of view it's nearly the same as asking if a plane can take off on smooth ice. A car can't move because of the lack of friction, but a plane wouldn't notice because it doesn't use friction to move.

 

[Xyclone]

Originally posted by: RapidSnail

Originally posted by: Citrix
<<<< RUNS OUT OF THREAD YELLING AND SCREAMING LIKE RICHARD PRYOR ON FIRE!!!!

It's impossible to escape this thread since it is on a treadmill that matches your forward motion exactly. Which begs the question, is stop, drop, and roll still feasible?

WRONG! You can exit by running backwards... through a corn field?

 

[smack Down]

Originally posted by: mugs

Originally posted by: waggy

Originally posted by: smack Down

Originally posted by: randay

Originally posted by: jagec

Originally posted by: randay
You have not addressed the issue that the treadmill can NEVER match the speed of the wheels relative to itself. Which makes the whole infinite-super-treadmill theory bunk.

Also the problem with what you believe is that you assume that the treadmill will stop once net motion is zero, thats not true since the wheels are still spinning and therefore the treadmill is still accelerating and angular momentum is still building. The treadmill will overcome the thrust of the engines(through angular momentum achieved by infinite acceleration and velocity), and then the airplane will accelerate backwards until it takes off anyway. granted, it will not take off very long since there will be no way to control it backwards, however it will gain an infinite amount of speed and eventually and messily, catch air.

Yes I have. Take your initial setup: Plane speed with respect to stationary object = P, treadmill speed with respect to stationary object = T, wheel speed = (P + T). If we try to match the treadmill speed to the wheel speed (T = (P + T)), this looks like a paradox until we realize that as long as the treadmill is accelerating, it can interact with the plane and reduce its speed. So the equation becomes (T = (P-AX) + T), where AX is the acceleration of the treadmill (A) times a term (X) which encapsulates the dimensions of the wheels and converts AX into a velocity. The treadmill has to accelerate at a rate where AX = P. If it accelerates faster, the plane moves backwards on the runway. If it accelerates more slowly, the plane moves forwards on the runway. Once the plane runs out of fuel, the treadmill must stop accelerating and continue at a constant speed.

The bolded portion is untrue. I said that the treadmill will stop ACCELERATING when the plane returns to the control position (its initial position on the runway). It will continue moving at a constant speed, with the wheels turning at a constant speed and angular momentum, with no acceleration and no buildup of further forces.

Explain please, why the treadmill will stop accelerating. The setup is thus: The treadmill will match the speed of the airplane in reverse. speed must be either air speed(same as "speed with respect to a stationary object"), or ground speed(treadmill is the ground). It cant be both, and so the underlined formula seems to be where you went wrong.

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.

It COULD be like a car - a car with the driving wheels off the treadmill and only the free-spinning wheels on the treadmill. No one would argue that such a car can move, but these people are two stupid to recognize that the driving wheels being off the treadmill is analogous to the jet engines of the airplane being independent of the treadmill. Such is life. C'est la vie.

It doesn't matter that a car is driving by it wheels. The wheels on the car create a force on the body of the car. It is just like the plane. What additional forces is there that can keep a car on stop on a treadmill compared to the plane?

 

[gorcorps]

Originally posted by: smack Down

It doesn't matter that a car is driving by it wheels. The wheels on the car create a force on the body of the car. It is just like the plane. What additional forces is there that can keep a car on stop on a treadmill compared to the plane?

Yes it does. Like I said a few posts up the car propels itself by friction on the wheels whereas a plane propels itself by a force of air being pushed behind it. The wheels on the plane do nothing more than make for smooth landing and takeoff. The wheels on a plane create absolutely no force to hinder the forward motion of the thrust. Wheels will be spinning with the treadmil but won't effect the body of the plane at all.

 

[smack Down]

Originally posted by: jagec

Originally posted by: FoBoT
nobody said the treadmill has a magic speed sensing control system. i don't remember anything like that in the original thingy
but is doesn't matter anyway, see yoyojelloman's bag analogy above ^^^

"magic"? Did the guy who installed the cruise control on your car have to put on his robe and wizard hat first?

From the original problem:

?Imagine a plane is sitting on a massive conveyor belt, as wide and as long as a runway. The conveyer belt is designed to exactly match the speed of the wheels, moving in the opposite direction. Can the plane take off? ?

But first you need to realize that I agree with the bag analogy above, and the case that I and a few others are arguing is the second interpretation of the problem, which is slightly more complex. I have stated this in several of my previous posts in this very thread.

Originally posted by: randay

Oh I see, you're smack down? He goes with the same torque/angular momental arguement and he also makes up the same convenient "control system".

Untrue. Smack down's "conversion" to angular momentum only occurred after he realized that his argument was unsound, and so he tried to borrow mine but screwed up on the details. I don't think he understands the principles of my argument at all.

Look, it's not hard to understand. There MUST be a control system for this problem to work at all. There are two ways to program this control system, depending on how you interpret the initial problem:
First (most reasonable, easiest to understand, and probably correct):
A stationary sensor measures the speed of the plane, and feeds that number directly into the treadmill, which runs in reverse. Net result: The plane rolls down the runway and takes off easily, with the wheels spinning more quickly than normal.

Second (interesting thought experiment, but people are getting hung up on semantics):
The speed of the treadmill is controlled via a speed sensor in the wheels, which attempts to equalize the speed of the wheels with that of the treadmill, but in the opposite direction. A mathematically identical, but conceptually easier scenario is a position sensor on the plane, and a control system on the treadmill which attempts to keep the plane fixed in position by adjusting treadmill speed and acceleration.

Now, IF the treadmill has no way to change the position of the plane, the control system will just continuously accelerate to try and match the wheels, until it burns out and/or reaches infinity.

HOWEVER, the plane and the treadmill are coupled via two terms: Frictional forces in the wheel hub, and angular momentum of the wheels. As such, if the treadmill accelerates quickly, it can actually build up a linear force at the wheel hub. If it accelerates fast enough, it can actually match the force provided by the engines, and the plane remains stationary. Given the small mass of the wheels and the low frictional forces, this requires fairly ludicrous amounts of acceleration, and as such a real-world treadmill could not use this effect to stop a plane from taking off. But if you allow boundless acceleration, you will find that the treadmill is capable of holding the plane at a standstill until its fuel reserves are exhausted, at which point the amount of angular momentum tied up in the wheels is twice the energy content of the fuel, after you subtract engine inefficiencies and frictional losses. The treadmill (and the wheels) will be moving at an extreme, but non-relativistic, rate of speed.


/edit: Dammit, I am NOT trolling you. Smack down might have been, I'm not sure. By all means poke holes in my arguments, send me nasty PMs, whatever, and if you can prove me wrong DO so. But don't discard my argument as without merit until you have fully understood it!

Sorry but you're not the first to come up with that argument. I posted it in the last thread about air plane on a treadmill and even found a video showing that the treadmill can affect the speed of a free spinning wheel. It was a wheel on a belt sander using a rubber band as an axle it jumped back when turned on. That is when randay had to abandon talking about the difference between a car and a plane and instead came up with this theory that the plane takes off backwards.