MouthBusters

[oosyxxx]

/summons Spiritwalker

 

[haarg]

You use something like a laser to detect any attempt at forward motion by the plane and as soon as any attempt is detected, you move the conveyor in the opposite direction to match the speed of the plane.

You don't specify what you mean by 'speed of the plane'.

I'm not clear on what your three scenarios are, as I only see two. One in which the conveyor matches speeds relative to a bystander. This case is very simple with an obvious answer. But it is the only situation many people think of when presented with the question, so they don't understand how someone could disagree.

The other situation is where the conveyor matches the speed of the wheels. In an ideal situation, the conveyor could prevent the plane from taking off. But I don't think you could physically build anything that would accurately simulate the ideal. Either the plane would take off, or its wheels would burn up. Contrary to what many people have stated, the wheels aren't irrelevant in this situation. It isn't the friction that matters, but their rotational inertia.

 

[Rukee]

Q, I suggest you get to a computer you can view youtube on and watch those two clips I posted(4 with the two from the show). They show exactly what happens. If you want a physics guy explaining physically and mathematicly what is happening and how it happens, watch this one too.
http://www.youtube.com/watch?v=siYQU99VaAM

 

[oosyxxx]

We could cure this thread of dullness if Q and Rukee posted .png's of their nards and then someone took the liberty of animating a duel between the two mangy sets.

 

[oosyxxx]

yes, once the plane overcomes the friction of the ground, all it cares about at that point is the amount of air it needs to move in order to generate thrust and lift.


regardless of what the belt is doing, if the plane is held in a stationary position, the only thing it needs to worry about is the air.
Now, if the belt is moving at mach 2, and the plane is moving with it, then you might have issues.

Oh, f'real?

 

[Sir_Brizz]

unbelievable...

 

[Rukee]

Contrary to what many people have stated, the wheels aren't irrelevant in this situation. It isn't the friction that matters, but their rotational inertia.

rotational inertia is going to hold the plane back? what? How do you figure the energy of the wheels rolling round on it`s axes is going to be the force to hold the plane back and not their friction at the axes?? If that was true, then the rotational inertia would slow or stop the plane as it approached take off speed, which is doesn`t. When the plane takes off aren`t the wheels still rolling while the plane is in the air? If your right, why then wouldn`t the wheels rotational inertia make the plane crash? or skid to a stop at the end of the runway? Or blow up or crash when the plane touches down and the wheels violently spin up and all that rotational inertia is instantly obtained?
The only way the treadmill could hold the plane back would be to go sooo incredibly fast that the wheels melt off the plane. Which is not how the question was originally stated.
The original question was: A plane is on a runway that is a giant conveyor belt. As the plane moves forward, the conveyor will exactly match that speed but in the reverse direction.
Can the plane take off?
The question wasn`t can we make the planes wheels melt off with a treadmill speed that`s unrealistic(and unobtainable) to keep the plane stationary?
Adding weight to the plane will only effect one thing. The effort needed to move the treadmill, nothing else would change. Once it`s rolling resistance is overcome by the thrust, it will accelerate away too
I don`t understand how a physics guy could have missed the trick in the question as well. Which I`ve brought up an a number of occasions, yet both of you refuse to acknowledge. Read the question, the treadmill speed = planes forward speed. If the plane was to be held stationary (by whatever means) then the planes forward speed would = 0, and the treadmill speed would = 0. Therefore it`s physically impossible for the treadmill to keep the plane stationary as the question is presented.
Besides that, this is an extremely easy problem. The rolling resistance of the wheels could be measured with a scale attached to the front of the plane and read what the value is to move the plane forward. Putting the plane on a running treadmill and reading the same scale would show nearly the exact same value. Therefore it doesn`t take anymore thrust to accelerate the plane on a moving treadmill then it does on a runway. This myth is soo busted, it`s not even funny.
I`m serious about writing your professor Q, I promise not to mention your name more then two or three times, I want his e-mail addy.