Uncivlengr,
The only reason I keep repeating myself is because people still don't understand what I am trying to say, so please forgive me, but I will have to repeat myself one more time, but hopefully this will make a little more sense.

Look at it this way, a conveyor belt is basically like a big, oblong tire in that it rotates around a fixed axis. The speed of the plane in relation to the belt is measured by the speed of the rotation of its' tires. (This is demonstrated by the clip from YouTube) The myth is essentially saying that the rotation of the belt must always be the same as the rotation of tires on the plane, in effect, keeping the plane stationary in relation to the ground. The myth asks if the plane is able to take off, given these conditions. The myth busters proved that the belt cannot physically keep the plane from taking off, however, in order for the plane to move forward in relation to the ground, (thus having the necessary air-flow over the wings for lift) the speed of the rotation of the tires must EXCEED the speed of the rotation of the belt. Unfortunately, that is not allowed by the myth. As a result, if the conditions set by the myth are kept, the plane must never move forward in relation to the ground which effectively keeps the plane on the ground and confirms the myth. Granted, it isn't confirmed because of the reason most people think, (that the belt can actually physically keep the plane from moving) but because the plane could never move forward in relation to the ground without exceeding the speed of the belt.

Yes, they busted the intent of the myth, but they had break the confines of the myth to do it. Does that make more sense?

I am new to this message board. Is there a way to actually get the MythBuster's take on this, or do we just hope they read it?

Rational,

I posted my last message as you were posting yours so I didn't respond to it. As to "unadulterated idiocy," if you had paid attention to the show or the hundreds of times it was explained on this thread, you would realize that the tarpaulin did NOT pose any greater difficulty for the plane. This thread is full of explanations of that. I won't bother repeating them. If you watched the clip on YouTube that I linked, I think you would see that option "1) Relative to the belt," is how they tested it. If you have not watched it, it would suggest you do so.

Here is what you are trying to say.

You believe the speed of aeroplane should be measured relative to the belt and NOT relative to the ground and as the belt should be set to this speed.

In mathematical terms this gives

Vb = -Vpb (1)

Where
Vb = Velocity of belt relative to the ground
Vpb= Velocity of plane relative to belt

Then you go on to observe correctly that if the plane moves then the condition above is violated, in mathematical terms this is shown by simply adding velocities in the reference frames

Vpg = Vpb + Vb (2)

where the new term
Vpg = Velocity of plane relative to ground

We can substitute (2) into (1) and rearrange which gives

Vb = Vpg + Vb

which can only be true if Vpg is zero, i.e. the plane doesn't move relative to the ground.

But if we accept that the control system will accelerate the belt in an attempt to satisfy (1) then it is possible under certain conditions to bring the plane to a halt through forces applied to the wheels as they accelerated. I gave a calculation on page 140 of this thread that the acceleration of the belt required is 144ms-2 to keep a Boeing 747 stationary.

People who claim that it is not valid to consider the velocity of the plane relative to the belt because any movement of the plane will violate (1) should consider that in the real world with inertia that (1) would not be satisfied instantaneously even in the case of measuring the speed of the plane relative to the ground because the belt could not immediately accelerate to the right speed, there would always be a lag.

Considering the speed of the plane relative to the belt would simply increase the length of the lag and the system may be unstable.

quote:

Originally posted by Javaman:
Rational,

I posted my last message as you were posting yours so I didn't respond to it. As to "unadulterated idiocy," if you had paid attention to the show or the hundreds of times it was explained on this thread, you would realize that the tarpaulin did NOT pose any greater difficulty for the plane. This thread is full of explanations of that. I won't bother repeating them. If you watched the clip on YouTube that I linked, I think you would see that option "1) Relative to the belt," is how they tested it. If you have not watched it, it would suggest you do so.

If you accept that the MBs did provide a harsher test then why oh why oh why did you keep wittering on about the MBs moving the tarpaulin faster than they should?

It is obvious you have confused two issues.

1) How the speed of the aeroplane should be measured, whether relative to the ground or the belt
2) The fact that the tarpaulin was moving faster than the aeroplane and that this did not conform to the myth spec, which is a very stupid point.

If you really want to make a case for (1) then I suggest you drop all your invalid comments about (2) and focus on the main issue (1).

I have watched all of the videos and read all of this thread, you have not. You are only beginning to understand the issues and you still have a long journey to go.

Rational,
First of all, there is much about this myth that is hypothetical, regardless of what view you take. Obviously, a conveyor belt cannot instantaneously adjust it's speed to the plane. I believe they even say that in the episode, but they make the case from the hypothetical situation where it could. My comments are based upon that assumption.

Second, I do NOT agree that the MBs provided a harsher test. The conveyor belt has absolutely no negative effect on the plane's ability to move forward. I have never said that they moved the tarpaulin faster than the plane. I said just the opposite. They moved the plane faster than the tarpaulin. That was the condition they violated.

I have not confused the two issues. They are both valid and relevant. Assuming you rearrange the words in point 2) to what I said - the plane moves faster than the tarpaulin - this has everything to do with the myth and is not a stupid point. There would be no point in the myth if the plane could move faster than the belt. That is why it is in there. As to point 1) - rather than just claiming to know better, please site specific examples from the episode, as I did, that indicate they weren't measuring the speed of the plane relative to the belt.

I assure you, I may be late coming on, but I assure you, I fully understand the issues. My issue, which you fail to grasp no matter how many times I say it, is not with the physics, yet you continue to argue physics with me.

What it boils down to is point 1). There is enough proof in the episode to justify the view of vpb=-vb. If we can agree on that, then point 2) is absolutely critical because it is THE MOST IMPORTANT condition set by the myth. If you don't agree with me on point 1), then please show me how you come to your conclusion and discuss that with me rather than arguing physics with me that I already agree with.

quote:

The myth is essentially saying that the rotation of the belt must always be the same as the rotation of tires on the plane, in effect, keeping the plane stationary in relation to the ground.

First of all, the myth doesn't say anything about the tires, and airplane speed isn't measured from the tires.

Of course, that's been pointed out already hundreds of times.

Secondly, the myth says nothing about keeping the plane stationary, either - that's an incorrect assumption on your part, nothing more.

The only interpretation that makes any sense is that the speed is measured relative to the ground (or air, to be precise). If you want to argue the entire problem is paradoxical in nature and physically impossible (which is the case in any other interpretation), you're wasting your time trying to argue how they should have busted it.

quote:

I am new to this message board. Is there a way to actually get the MythBuster's take on this, or do we just hope they read it?

The fact that there's a post from the producer of the show explaining in no uncertain terms why they've busted the myth should be an indication that they won't be revisiting this one again.

Uncivlengr,

Forgive me, but, I linked a video, told what parts to pay attention to, and quoted parts of what they said which all back up the argument that they are measuring the speed of the plane in relation to the belt. It would be incredibly helpful if you could do the same to prove otherwise. No, the myth doesn't say those things, but neither does it say that it is relative to the ground either. I'm not arguing how they should have busted it, I am arguing that they had to negate the main point of the myth in order to bust it. Please, there is no point in arguing what they related the speed of the plane to unless you can show me in the episode where they say something other than what I have already sited. I brought proof. Tag, you're it.

Airplane speed is measured relative to the air - there's no speedometer in the wheels.

Car speed is measured by the rotation of the transmission, and consequently, the wheels.

Cars and planes aren't similar, in their propulsion method or speed measurement. While the Mythbuster's comparison to a car is questionable (as has already been established), their interpretation of the myth, as applied to a plane, is not.

Good lord, won't some moderator take pity and close this thread of epic fail? 230+ pages of redundant drivel has been quite enough, thank you.

quote:

Originally posted by Javaman:
1). There is enough proof in the episode to justify the view of vpb=-vb.

The Mythbusters' interpretation, or at least, presentation, of the myth is IRRELEVANT! If they presented it incorrectly, SO WHAT! The MYTH does NOT say that the plane is held motionless relative to the ground, you only ASSUME that it is held motionless, and this assumption is INCORRECT!

If the Mythbusters were to revisit this myth,it would only be to clarify the confusion about the conditions set forth by the riddle, and would not be to retest the myth. It is well and truly BUSTED. Get over it.

quote:

Originally posted by Javaman:
If we can agree on that

We don't, and so this discussion is over.

quote:

Originally posted by Javaman:
I brought proof. Tag, you're it.

http://www.youtube.com/watch?v=0ul_5DtMLhc 0:29-0:42:

"If a manned airplane is on a conveyor belt, and both are going at the airplane's takeoff speed, but in opposite directions, will the plane be held where it is, or will it take off?"

This CLEARLY states that they understood and were testing the correct interpretation of the myth.

Your argument is BUSTED, just like the myth.

quote:

Originally posted by EnderGT:

quote:

Originally posted by Javaman:
Ender,

I am not disputing the physics. I understand all that. This whole thing boils down to what the speed of the plane is in relation to. If it is to the outside observer, then you are absolutely correct. If it is to the conveyor belt, then I believe what I am saying is correct. All that needs to happen is find out if they ever made reference to the plane's speed with relation to the conveyor belt. Unfortunately, I did not record the episode and have no way to review it.

The wording that is on the Episode Wiki unfortunately SEEMS to indicate that the speed is relative to the belt due to its wording:

"Can an airplane on a conveyor belt running in opposite motion to the airplane's tires at the same speed keep the plane from taking off?"

However, the original riddle contains no such wording:

"A plane is standing on runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction). Can the plane take off?"

The wording that is on the Mythbusters Wiki is the unfortunate result of people trying to indicate that the plane does, in fact, have wheels. I do not consider the wording on the Mythbusters Wiki to be accurate, much less definitive. Additionally, I think there is enough wiggle room in that wording to argue that it does not stipulate measuring the speed of the plane relative to the conveyor.

If you understand the physics, as you claim to, then you should understand that there is no way that the conditions of the riddle, as you claim them to be, can be met if the plane is generating thrust. If the plane isn't allowed to generate thrust, then of course it won't take off.

You are grasping at straws, the obvious implication of the episode wiki is that the speed of the plane is measured relative to the belt and the wording of the myth you prefer is simply ambiguous as to where the speed should be measured from.

quote:

Originally posted by EnderGT:

quote:

Originally posted by Javaman:
I brought proof. Tag, you're it.

http://www.youtube.com/watch?v=0ul_5DtMLhc 0:29-0:42:

"If a manned airplane is on a conveyor belt, and both are going at the airplane's takeoff speed, but in opposite directions, will the plane be held where it is, or will it take off?"

This CLEARLY states that they understood and were testing the correct interpretation of the myth.

Your argument is BUSTED, just like the myth.

On the contrary, the video implies that the aeroplane's speed is measured relative to the belt, not the ground. When it asks "if a plane at take off speed would take off", if the speed described was measured relative to the ground then it would be flying already and there would be nothing to work out!!

Your interpretation is UTTERLY WRONG!

Clearly for the myth to be any sort of intellectual challenge has to ask the reader to predict the outcome of the conditions described

What it is obviously asking the reader to consider is an initially stationary plane which attempts to take off and a belt with a control system which attempts to prevent take off by matching its speed. Therefore whether the plane reaches take off speed is a question for the reader of the myth to consider, it is not pre-defined.

So your citation unfortunately confirms the exact opposite of your intended point. The video is in effect asking if the plane was moving relative to the belt at take off speed, and the belt was moving backwards at the same speed what would happen? Would the plane take off?

The question is problematic of course because underneath it are a number of paradoxes but as formulated the interpretation you offer is wrong.

quote:

Originally posted by -rational-:

quote:

Originally posted by EnderGT:

quote:

Originally posted by Javaman:
I brought proof. Tag, you're it.

http://www.youtube.com/watch?v=0ul_5DtMLhc 0:29-0:42:

"If a manned airplane is on a conveyor belt, and both are going at the airplane's takeoff speed, but in opposite directions, will the plane be held where it is, or will it take off?"

This CLEARLY states that they understood and were testing the correct interpretation of the myth.

Your argument is BUSTED, just like the myth.

On the contrary, the video implies that the aeroplane's speed is measured relative to the belt, not the ground. When it asks "if a plane at take off speed would take off", if the speed described was measured relative to the ground then it would be flying already and there would be nothing to work out!!

Your interpretation is UTTERLY WRONG!

Clearly for the myth to be any sort of intellectual challenge has to ask the reader to predict the outcome of the conditions described

What it is obviously asking the reader to consider is an initially stationary plane which attempts to take off and a belt with a control system which attempts to prevent take off by matching its speed. Therefore whether the plane reaches take off speed is a question for the reader of the myth to consider, it is not pre-defined.

So your citation unfortunately confirms the exact opposite of your intended point. The video is in effect asking if the plane was moving relative to the belt at take off speed, and the belt was moving backwards at the same speed what would happen? Would the plane take off?

The question is problematic of course because underneath it are a number of paradoxes but as formulated the interpretation you offer is wrong.

Woah, chill... I posted that video only to refute Javaman's claim that the Mythbusters interpreted the myth such that the plane was to be held still. I believe the video provides a solid refutation of his claim.

I'm in agreement with you - the initial conditions state that all bodies are motionless.

An airplane takes off when the speed of the air hitting the wing is it's takeoff speed.It doesn't make sense that both the airplane and the conveyer belt were going 20MPH and it still moved foreward The airspeed indicator measures the speed of the air flowing under the wings. The airplanes wheels were acually spinning 40MPH. The airplane was moving foreward 20MPH when it tookoff. with or without the conveyerbelt it was going to takeoff.

If they don't understand by now, then they never will. I can't beleive this thread is still going.

An airplane is not a car.

I am going to attempt to stop this thread by officially declaring this thread stopped!

[Something like standing in front of a column of tanks]

quote:

Originally posted by EnderGT:

Woah, chill... I posted that video only to refute Javaman's claim that the Mythbusters interpreted the myth such that the plane was to be held still. I believe the video provides a solid refutation of his claim.

I'm in agreement with you - the initial conditions state that all bodies are motionless.

Your point was completely invalid.

The commentary in the clip you cited makes it clear that the speed of the plane has to be measured relative to the belt NOT the ground and that leads to the very complex scenario with accelerating belts which can potentially cause the aeroplane to be held in place by the belt because of the forces exerted on accelerating the wheels.

Ender,

You just said that you agree with Rational, yet that is what I have been arguing with you about this whole time. I said that there was enough evidence in the myth to support vpb = -vb. which is exactly what Rational just said. That is the starting point of the myth. The test is to see if the plane can take off from those conditions. What I have just written is no different than what you just agreed with rational about. What I have been getting at is what comes after that. Please note that I have said several times that I do NOT think that what I am going to say was the intent of the myth. It is simply a snare in the conditions that were set, yet it is fact - the conditions state that the belt can adjust it's speed to that of the plane instantaneously, thus, the speed of the plane in relation to the belt can never be greater than that of the belt. Are you with me so far? The problem with the myth is that in order for the plane to "bust the myth," it must move faster than the belt. As the mythbusters proved, that is no problem at all. The problem is that by moving faster than the belt, the hypothetical situation of the belt being able to match the speed of the plane is no longer true. But since it is a condition of the myth, then the plane must never move faster than the belt an in essence, remain at zero velocity in relation to the ground. I you think about it, there is no way you can refute this. Again, I don't believe this was the intent of the myth.

You said, "If the Mythbusters were to revisit this myth,it would only be to clarify the confusion about the conditions set forth by the riddle, and would not be to retest the myth."
I agree with you 100%. It would be pointless to devote an episode to watching a plane sit on the ground.

Scubasteve,

this discussion isn't over the phy