Mythbusters punk'd whole internet

[Throckmorton]

Originally posted by: spidey07

Originally posted by: Kev

That's not true. Acceleration of the treadmill creates an opposing force to the plane's engines. This has been explained, calculated, and diagrammed umpteen times in this thread. I

It's not even possible for the treadmill to create an "opposing force to the plane's engines." All the explanations, calculations, and diagrams that "support" this are flat out wrong. The only force that the treadmill creates is on the wheels of the plane. As soon as the plane begins to generate thrust, it will move forward no matter how fast the treadmill and wheels spin, because there is no force opposing the body of the plane. The plane's speed is not dependent on the speed of the wheels. The wheels are simply there to create a low friction surface for the plane to accelerate over.

And here lies the disconnect.

You believe the plane can overcome the forces of the treadmill. This is fail at physics.

According to the problem there is no way the plane can move.

Stand on a treadmill wearing skates, with a rope tied to the wall. Can you pull yourself along the treadmill or is the friction in the wheel bearings greater than the strength of your muscles? The problem doesn't say the treadmill moves fast enough to counteract the plane's engines. That would defeat the purpose of the riddle... The treadmill turns backwards at the same speed the plane is moving forwards.

 

[spidey07]

Originally posted by: Throckmorton
Stand on a treadmill wearing skates, with a rope tied to the wall. Can you pull yourself along the treadmill or is the friction in the wheel bearings greater than the strength of your muscles? The problem doesn't say the treadmill moves fast enough to counteract the plane's engines. That would defeat the purpose of the riddle... The treadmill turns backwards at the same speed the plane is moving forwards.

That's why it's a paradox.

If the treadmill could magically match any velocity I my have relative to ground then yes I would be unable to pull myself forward.

That's what I've been saying the entire time. That's why by definition of the problem there is infinite acceleration of the treadmill because dV/t is dV/zero.

 

[SlitheryDee]

Originally posted by: spidey07

Originally posted by: Throckmorton
Stand on a treadmill wearing skates, with a rope tied to the wall. Can you pull yourself along the treadmill or is the friction in the wheel bearings greater than the strength of your muscles? The problem doesn't say the treadmill moves fast enough to counteract the plane's engines. That would defeat the purpose of the riddle... The treadmill turns backwards at the same speed the plane is moving forwards.

That's why it's a paradox.

If the treadmill could magically match any velocity I my have relative to ground then yes I would be unable to pull myself forward.

That's what I've been saying the entire time. That's why by definition of the problem there is infinite acceleration of the treadmill because dV/t is dV/zero.

Wait this doesn't work when the treadmill matches your velocity relative to the ground. It only works when the treadmill is matching the speed of the wheels and becomes locked into endless acceleration the moment they start moving.

How could the speed of the treadmill become infinite if it's only matching the speed of the plane relative to the ground? That's the scenario where the plane takes off I think.

 

[randay]

Originally posted by: spidey07
That's why it's a paradox.

If the treadmill could magically match any velocity I my have relative to ground then yes I would be unable to pull myself forward.

That's what I've been saying the entire time. That's why by definition of the problem there is infinite acceleration of the treadmill because dV/t is dV/zero.

So you are suggesting a magic treadmill and you wonder why people dont understand what you are trying to say, or even take you seriously? Not to mention you are still referencing some totally incorrect version of PoaT.

 

[spidey07]

Originally posted by: randay

Originally posted by: spidey07
That's why it's a paradox.

If the treadmill could magically match any velocity I my have relative to ground then yes I would be unable to pull myself forward.

That's what I've been saying the entire time. That's why by definition of the problem there is infinite acceleration of the treadmill because dV/t is dV/zero.

So you are suggesting a magic treadmill and you wonder why people dont understand what you are trying to say, or even take you seriously? Not to mention you are still referencing some totally incorrect version of PoaT.

LOL, no what I've been trying to say is people are very bad with word problems and can't properly translate them into the physics involved.

It's an IQ thing. Once you get to a certain level you can understand.

 

[randay]

Originally posted by: spidey07

Originally posted by: randay

Originally posted by: spidey07
That's why it's a paradox.

If the treadmill could magically match any velocity I my have relative to ground then yes I would be unable to pull myself forward.

That's what I've been saying the entire time. That's why by definition of the problem there is infinite acceleration of the treadmill because dV/t is dV/zero.

So you are suggesting a magic treadmill and you wonder why people dont understand what you are trying to say, or even take you seriously? Not to mention you are still referencing some totally incorrect version of PoaT.

LOL, no what I've been trying to say is people are very bad with word problems and can't properly translate them into the physics involved.

It's an IQ thing. Once you get to a certain level you can understand.

There are a lot of people here who understand that the treadmill can oppose the airplane. Too bad you are the one who seems to be very bad with word problems, since you seem to want to try and solve the impossible(paradox) version instead of the logical real-world version.

wanna bet on which version of the question mythbusters is going to bust? Im pretty sure they dont believe in magic over there.

 

[spidey07]

Randay, part of being intelligent is to see all the possibilities without constraints of what you can touch and feel.

I did not attempt to solve the impossible, only to point out that it is a paradox. Still infinite > finite.

 

[randay]

Originally posted by: spidey07
Randay, part of being wrong is to see all the impossibilities without constraints of what you can touch and feel.

fixed

I did not attempt to solve the impossible

yes you did.

Still infinite > finite.

infinity is not a number.

 

[bigal40]

I see someone calculating the force of friction that the plane would need to overcome using the coefficient of friction between rubber and asphalt but that is completely wrong. The wheels would be rolling meaning that at any given instant the part of the wheel in contact with the asphalt has a velocity of zero relative to the asphalt and there is no frictional force there.

The only force acting on the plane are
1)gravity
2)the normal force of the ground
3)the force of lift caused by the wings
4)wind resistance
5) the thrust of the engines
6)frictional force in the wheel bearings

Obviously gravity and the normal cancel each other out and the force of lift by the wings will make the plane fly.

The thrust of the engines should easily be able to overcome wind resistance + frictional force of the wheel because the engines always overcome the wind resistance while the plane is in flight and the frictional force caused by the wheel bearing should be almost non existent.

If you put a car on a treadmill, yes it would not move and would not have any air moving over its wings(if it had wings), but a plane is not pushed forward by its wheels it is pushed forward by its engines which are pushing on the air so the plane will move.

The only way I could not see the plane taking off is if the treadmill was going so fast that the force of friction in the wheel bearing was actually greater that the thrust of the engines. While I don't have any idea of what speed this would be it is going to be much faster than any treadmill big enough for a plane could be built to go.

 

[Q]

Someone fill me in, what happened?

 

[her209]

Originally posted by: Quintox
Someone fill me in, what happened?

The plane took off.

:laugh:

 

[spidey07]

Originally posted by: her209

Originally posted by: Quintox
Someone fill me in, what happened?

Mythbusters could not stay within bounds of the problem.

:laugh:

fixed.

-edit-
Seriously, can you guys not dissect this? Or are you still so stuck with what you learned in physics/dynamics/statics. I profess that I'm not an idiot. I understand. I can draw free body diagrams with the best of them, that isn't difficult. Although it's been a while.

It's a freaking paradox of Newtonian physics.

 

[her209]

Originally posted by: bigal40
The wheels would be rolling meaning that at any given instant the part of the wheel in contact with the asphalt has a velocity of zero relative to the asphalt and there is no frictional force there.

How is it wrong?

You have a 1 kg box sitting on the floor. Assume us between the box and ground is 0.5. You stand next to the box and push against it with a force of 4 N.

1. Does the box slide?
2. What was the box's velocity relative to the ground?
3. Was there frictional force there?

 

[her209]

Originally posted by: spidey07

Originally posted by: her209

Originally posted by: Quintox
Someone fill me in, what happened?

Mythbusters could not stay within bounds of the problem.

:laugh:

fixed.

-edit-
Seriously, can you guys not dissect this? Or are you still so stuck with what you learned in physics/dynamics/statics. I profess that I'm not an idiot. I understand. I can draw free body diagrams with the best of them, that isn't difficult. Although it's been a while.

It's a freaking paradox of Newtonian physics.

I already pointed out how the plane could move forward without breaking the bounds of the problem.

 

[sao123]

Originally posted by: astroidea

Originally posted by: Kev

Originally posted by: uclaLabrat

Originally posted by: astroidea
The plane takes of depending on which plane it is!

So the main argument that the plane would still take off is that there's no counter force keeping the plane from moving forward as the thrust of the plane is independent from the wheels. So as long as the wheels roll freely, the plane will still take off.

However, there is a counter force! Rotational friction. There is a frictional force in the bearings of the wheels. It does not roll completely freely without any opposing forces. The thrust force the plane puts out would be needed to counteract this frictional force.
Therefore, the quicker the wheels spin, the more force the plane would have to put out to spin the wheels.
But isn't the conveyer belt pushing the same amount of force on the wheels in the opposite direction?
So when would the plane actually move forward relative to the air?
Well first, let's imagine this situation:
The plane is on a conveyer belt that's moving backwards at 100mph. The plane is moving forwards at 100mph also. So right now, the plane isn't moving relative to the air right? But what would happen if the plane suddenly stopped all its engines? The coveyer belt would begin to move the plane backwards. It would no longer be able to maintain the static air speed.
Therefore, we can reasonably deduce that it does indeed take some force from the plane's thrust in order to counteract the motion of the conveyer belt.
So how much force would it take to keep the plane stationary with the air when the belt is moving backwards at 1000000000000 miles per hour? Would the plane have enough power to keep it stationary? Probably not.
But then again, is it even possible for the tires to still be in contact with the treadmill at 100000000000 miles per hour? According to newtonian physics, once the frictional force of the bearings exceed the frictional force between the tires and the surface of the conveyer belt, wouldn't the tires lose grip with the surface? Once the tires lose surface, the plane will only have to generate enough thrust to counteract the frictional force between the tires and the surface of the belt in order to move forward.

So therefore, the plane will move forward, but only when the plane is able to generate enough thrust for the friction of the tires to break free from the belt.

But is there any plane that has a powerful enough engine that can generate enough force to break free?

Let's look at the Boeing 777.
According to wikipedia, it generates 418,000N of thrust, and has a mass of 139,225kg.
The coefficient of static friction between tires and tarmac is about 0.7.
If you work out the math, µmg is (0.7)(139225)(9.8) = 956,058N.
This is over twice as much force as what the 418,000N of thrust the engines put out.
And if you consider the hundreds of opposing forces that I haven't accounted for, it's even less likely to be able to break free from the friction.
Thus, Plane DOESN'T TAKE OFF

But what if you had a plane with a better weight to thrust ratio?
Well, I let's look at the F22 Raptor.
According to wikipedia, the two turbofan engines generates a total of 311,000N of thrust. The plane when empty has a mass of 14,365kg.
So given that, let's work out the math again. (0.7)(14365)(9.8) = 98,544N
In this case, the 311,000N of thrust is significantly greater than 98,544N of frictional force. So in this case, the plane would take off!

In conclusion: THE PLANE MAY OR MAY NOT TAKE OFF DEPENDING ON WHICH PLANE IT IS!

OMG. Someone else understands friction and thrust!

How reassuring. Nice work on the analysis btw. Most coherent and lucid I've seen thus far.

And yet he's still wrong.

Oh really. Well why don't you enlighten us in how the argument is flawed.
:roll:

because the initial starting condition is impossible to achieve. The poster assumes to be true the exact argument he is trying to prove is possible.


Lets assume that his opening condition is true...

1)The conveyor belt is moving at velocity -X.
2)The plane is moving at velocity X with respect to the conveyor belt.
3)The entire conveyor system is not moving with respect to a universal fixed point, (for example: the atmosphere.) providing a ?D of 0 for the plane.
4)The plane exerts a force on and recieves a counter acceleration with respect to our universal fixed frame.

An object undergoing acceleration must have a ?V, and therefore a ?D cannot be 0...
Contradiction.

The problem is: This plane cannot be be stationary and in motion at the same time.

 

[effee]

This thread will never end.

Plane takes off btw.

 

[mugs]

Originally posted by: spidey07

Originally posted by: her209

Originally posted by: Quintox
Someone fill me in, what happened?

Mythbusters could not stay within bounds of the problem.

:laugh:

fixed.

-edit-
Seriously, can you guys not dissect this? Or are you still so stuck with what you learned in physics/dynamics/statics. I profess that I'm not an idiot. I understand. I can draw free body diagrams with the best of them, that isn't difficult. Although it's been a while.

It's a freaking paradox of Newtonian physics.

Can you show me where in this thread the wording of the problem was stated?

 

[jagec]

Originally posted by: spidey07
Seriously, can you guys not dissect this? Or are you still so stuck with what you learned in physics/dynamics/statics. I profess that I'm not an idiot. I understand. I can draw free body diagrams with the best of them, that isn't difficult. Although it's been a while.

It's a freaking paradox of Newtonian physics.

Only if you constrain the word "matches" to be "exactly identical to an infinite number of sig figs at all times."

By that definition no control system in the world performs as advertised. Your room thermostat can't hold the room at 70 degrees, your car cruise control can't keep your car at 60 miles an hour.

I understand your definition, I understand why you could call this a paradox, and indeed it is impossible for the treadmill to exactly match the speed of the wheels at all times, but that is true for every control system in the world! The question is whether the treadmill can keep the plane from taking off by attempting to match the speed of the wheels. In other words, the plane starts moving, the treadmill accelerates backwards to try and compensate for this, at first the wheels are just accelerated more but as the forces of friction and angular momentum begin to assert themselves, the forward motion of the plane is checked and it begins to roll backwards...at this point the treadmill has overshot the control condition, and will begin to reduce the rate of acceleration until the wheels are once again moving faster, then it will increase the rate of acceleration again, and so on until the plane runs out of fuel. The question is whether the backwards forces of friction and resistance due to angular acceleration can be sufficient to match the output of the plane's engines. The answer is Yes, BUT only if the plane's engines aren't powerful enough to literally break the wheels loose and drag them across the threadmill, AND the treadmill is powerful beyond all reason (certainly nothing built on THIS planet), and the wheels are indestructible.

Originally posted by: bigal40
The only way I could not see the plane taking off is if the treadmill was going so fast that the force of friction in the wheel bearing was actually greater that the thrust of the engines. While I don't have any idea of what speed this would be it is going to be much faster than any treadmill big enough for a plane could be built to go.

The force you omitted is angular momentum in the wheels, but that ends up being similar to friction in that it only becomes significant at VERY high treadmill speeds/accelerations.

I think that everyone arguing that the plane doesn't necessarily take off would agree with your bolded statement that it would be next to impossible, in the real world, to construct a treadmill powerful enough to hold the plane on the ground via only the weak forces of friction and angular momentum. And, interestingly enough, those forces at the hub can only increase to the point where the wheels themselves start sliding on the treadmill, which means that if your jet is powerful enough, it can take off even if placed on a treadmill of infinite acceleration...assuming it doesn't become a black hole first.

 

[randay]

Originally posted by: her209

Originally posted by: spidey07

Originally posted by: her209

Originally posted by: Quintox
Someone fill me in, what happened?

Mythbusters could not stay within bounds of the problem.

:laugh:

fixed.

-edit-
Seriously, can you guys not dissect this? Or are you still so stuck with what you learned in physics/dynamics/statics. I profess that I'm not an idiot. I understand. I can draw free body diagrams with the best of them, that isn't difficult. Although it's been a while.

It's a freaking paradox of Newtonian physics.

I already pointed out how the plane could move forward without breaking the bounds of the problem.

I dont think he understands that theres 2 sides to the problem. one where the treadmill tracks the airplane airspeed, and then the broken side where the treadmill tracks the airplanes groundspeed(ground being the treadmill itself). i keep telling him hes going off the wrong "question" but he seems to ignore that fact.

 

[natto fire]

LOL, this topic is quickly becoming a religion.

Clearly, the constraints of this riddle are determined however one individual to the next wants to interpret the question. Which does not exactly make it scientific. However, that is just great for a show like Mythbusters, because they are not always scientific themselves, and are mostly pandering to a crowd that wants to be entertained, much like most of Discovery Channel's audience these days...

 

[jjzelinski]

Originally posted by: effee
This thread will never end.

Plane takes off btw.

This is the thread that never ends, it just goes on and on my friend. Some people started ranting, not knowing they were dumb, and they just kept on ranting on forever just because this is the thread that never ends, it just goes on and on my friend. Some people started ranting, not knowing they were dumb, and they just kept on ranting on forever just because this is the thread that never ends, it just goes on and on my friend. Some people started ranting, not knowing they were dumb, and they just kept on ranting on forever just because is the thread that never ends, it just goes on and on my friend. Some people started ranting, not knowing they were dumb, and they just kept on ranting on forever just because is the thread that never ends, it just goes on and on my friend. Some people started ranting, not knowing they were dumb, and they just kept on ranting on forever just because is the thread that never ends, it just goes on and on my friend. Some people started ranting, not knowing they were dumb, and they just kept on ranting on forever just because is the thread that never ends, it just goes on and on my friend. Some people started ranting, not knowing they were dumb, and they just kept on ranting on forever just because is the thread that never ends, it just goes on and on my friend. Some people started ranting, not knowing they were dumb, and they just kept on ranting on forever just because is the thread that never ends, it just goes on and on my friend. Some people started ranting, not knowing they were dumb, and they just kept on ranting on forever just because is the thread that never ends, it just goes on and on my friend. Some people started ranting, not knowing they were dumb, and they just kept on ranting on forever just because the just like effee said, the plane takes off.

 

[Tweak155]

Originally posted by: Captain Howdy
LOL, this topic is quickly becoming a religion.

Clearly, the constraints of this riddle are determined however one individual to the next wants to interpret the question. Which does not exactly make it scientific. However, that is just great for a show like Mythbusters, because they are not always scientific themselves, and are mostly pandering to a crowd that wants to be entertained, much like most of Discovery Channel's audience these days...

The main difference here is, the ones that "believe" it will take off (lol), use the logic of any man made airplane and man made treadmill.

The ones that stick to the idea that it will not, need some scenario that can never be proven by experiment (at least currently).

I've stated a scenario could be rigged just to prove the point that it COULD restrain the airplane several times. But I refuse to stick to ignorance knowing it cannot be created.

Another note, I'm surprised all the people stating a treadmill with infinite velocity/acceleration could hold the plane still aren't somehow arbitrarily changing the plane design either. Does it sound so crazy to change the design of the plane? Then why are we doing it to the treadmill?

If we use a plane that can SAFELY fly (not just take off for 5 seconds then land because that is all it is capable of) and any treadmill made by man, this plane will take off.

 

[LTC8K6]

Do we all agree that a car cannot move given the scenario of the treadmill matching it's speed?

I think we do.

So let's take the same car and attach a jet engine to it.

Now let's put the car back on the treadmill, but do not start up the jet engine.

So we are still the same. The car can't go anywhere because the treadmill is matching the car's speed up to it's max.

Let's say the car's max is 110MPH.

So we have the car on the treadmill at WOT.

The car's speedo says 110mph, the treadmill indicates 110mph, and the car is stationary with it's wheels rotating at about twice the speed they would be on the ground. There will be some slip, but it's irrelevant.

Now if we light off the jet, the car will move forwards because the jet is unaffected by the wheel speed, or the matching treadmill speed.

The treadmill will continue to match the car's forward speed right up until the car leaves the treadmill under the jet's thrust, but this will not stop the jet from pushing the car forwards.

The only thing the jet has to overcome to move the car are the small forces of inertia, wheel bearing friction, and wind resistance, which it will do easily.

The car with the jet engine, and a plane, can move forwards on a treadmill that matches their forward speed. There is nothing to stop them.

The plane will easily take off on the treadmill that matches it's forward speed.

 

[her209]

Originally posted by: LTC8K6
Do we all agree that a car cannot move given the scenario of the treadmill matching it's speed?

I think we do.

So let's take the same car and attach a jet engine to it.

Now let's put the car back on the treadmill, but do not start up the jet engine.

So we are still the same. The car can't go anywhere because the treadmill is matching the car's speed up to it's max.

Let's say the car's max is 110MPH.

So we have the car on the treadmill at WOT.

The car's speedo says 110mph, the treadmill indicates 110mph, and the car is stationary with it's wheels rotating at about twice the speed they would be on the ground. There will be some slip, but it's irrelevant.

Now if we light off the jet, the car will move forwards because the jet is unaffected by the wheel speed, or the matching treadmill speed.

The treadmill will continue to match the car's forward speed right up until the car leaves the treadmill under the jet's thrust, but this will not stop the jet from pushing the car forwards.

The only thing the jet has to overcome to move the car are the small forces of inertia, wheel bearing friction, and wind resistance, which it will do easily.

The car with the jet engine, and a plane, can move forwards on a treadmill that matches their forward speed. There is nothing to stop them.

The plane will easily take off on the treadmill that matches it's forward speed.

The wheels of a car are not free spinning. A car moves by applying force at the wheels to the ground (or in this case, the treadmill).

 

[smack Down]

Originally posted by: LTC8K6
Do we all agree that a car cannot move given the scenario of the treadmill matching it's speed?

I think we do.

So let's take the same car and attach a jet engine to it.

Now let's put the car back on the treadmill, but do not start up the jet engine.

So we are still the same. The car can't go anywhere because the treadmill is matching the car's speed up to it's max.

Let's say the car's max is 110MPH.

So we have the car on the treadmill at WOT.

The car's speedo says 110mph, the treadmill indicates 110mph, and the car is stationary with it's wheels rotating at about twice the speed they would be on the ground. There will be some slip, but it's irrelevant.

Now if we light off the jet, the car will move forwards because the jet is unaffected by the wheel speed, or the matching treadmill speed.

The treadmill will continue to match the car's forward speed right up until the car leaves the treadmill under the jet's thrust, but this will not stop the jet from pushing the car forwards.

The only thing the jet has to overcome to move the car are the small forces of inertia, wheel bearing friction, and wind resistance, which it will do easily.

The car with the jet engine, and a plane, can move forwards on a treadmill that matches their forward speed. There is nothing to stop them.

The plane will easily take off on the treadmill that matches it's forward speed.

Sorry but weather a force is applied via the wheels or jet makes no difference. Draw a free body diagram and guess what in both case the force is applied to the body of the car.