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12/06/2006 04:42:45 PM · #151 |
Originally posted by Gordon:
Originally posted by jhonan:
In other words assuming the treadmill can keep up this ridiculously high level of acceleration, and we're talking thousands of miles per hour here, then the force would be enough to hold the plane in place no matter how much thrust you applied. |
Yes, but the original question does not state that the treadmill matches the force of the plane. If you rephrase it and say force instead of speed, then you are right.
F=ma, for huge a, you can generate a counteracting force which would keep the plane still.
However, the treadmill doesn't match the acceleration force of the plane. It matches the forward speed of the plane, which provides a massively smaller acceleration, consequently a much smaller force, which is vastly overwhelmed by the plane acceleration. |
Ah ha! Yes! But to match that forward speed it also has to match the acceleration, otherwise how would it get up to that speed? |
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12/06/2006 04:43:01 PM · #152 |
Originally posted by eqsite:
I'd like to turn the question around. How does the treadmill stop the plane from moving forward? How is the force from the treadmill imparted on the plane to counter the force generated by the engines? |
Now I understand both sides. The original question should state "Could a treadmill prevent an airplane from moving forward?"
I thought that the question implied a magic treadmill that DID prevent the plane from moving forward while "on" the treadmill. |
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12/06/2006 04:43:39 PM · #153 |
Originally posted by sodoff:
Originally posted by Gordon:
Originally posted by sodoff:
[quote=Gordon] [quote=sodoff]
No, you are assuming. I would like an explanation how you think there is no connection between plane speed and wheel speed. I may be a complete moron, but I understand that an aircraft from standstill can accelerate down a runway until it takes off. But now you are saying that the wheels don't speed up, go faster, whatever...as the plane goes faster. That they are not connected in anyway.
So why is there a treadmill?? |
Sorry, Gordon, but that doesn't answer my question. I have stated all along that the wheels move at a set speed in relation to the acceleration of the aircraft. The treadmill matches the speed of the wheels, so where is the forward motion coming from? [/quote
Yes, you've incorrectly stated that the wheels move at a set speed in relation to the acceleration of the aircraft.
I can't help that. |
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What do you mean, incorrectly?? Surely this is basic science a 12 year old can understand? |
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12/06/2006 04:43:46 PM · #154 |
Originally posted by sodoff:
What do you mean, incorrectly?? Surely this is basic science a 12 year old can understand?
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Do you have a rolling suitcase at home ? or a roller skate ? Or anything with wheels that do not provide thrust, but reduce friction ?
Spin those wheels. spin them faster. turn it upside down and just spin the wheel.
The rotation of the wheel does not drive the object. Often the speed is similar, but for example, if you held that suitcase on a treadmill, while the treadmill was moving - even very quickly, the speed of the wheels would not be matched by you accelerating the suitcase. You could also easily pull the suitcase forward, no matter how fast those wheels were spinning.
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12/06/2006 04:44:07 PM · #155 |
Originally posted by Zal:
Now I understand both sides. The original question should state "Could a treadmill prevent an airplane from moving forward?"
I thought that the question implied a magic treadmill that DID prevent the plane from moving forward while "on" the treadmill. |
Yes, that was my initial premise as well. But it is based on an assumption that is not explicit in the original post. |
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12/06/2006 04:44:56 PM · #156 |
Originally posted by Zal:
The only way to generate LIFT is to have airflow over the wings, either by moving the airplane (accelerating down a runway) or by moving the air (wind tunnel where the plane is stationary).
Do we all agree that unless the airplane is physically moving, it will not take off? |
Picture a Harrier Jump jet, zero land speed at lift off. I know that is cheating, but most military jets use their wings to stear, not for lift. Their lift comes from the turbines, If it can pull enough air into and the jets , it creates eough of the wind tunnel effect to get lift, not from the wings but by the direction of the exiting air
Message edited by author 2006-12-06 16:47:51. |
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12/06/2006 04:45:42 PM · #157 |
Originally posted by jhonan:
Originally posted by Gordon:
Originally posted by jhonan:
In other words assuming the treadmill can keep up this ridiculously high level of acceleration, and we're talking thousands of miles per hour here, then the force would be enough to hold the plane in place no matter how much thrust you applied. |
Yes, but the original question does not state that the treadmill matches the force of the plane. If you rephrase it and say force instead of speed, then you are right.
F=ma, for huge a, you can generate a counteracting force which would keep the plane still.
However, the treadmill doesn't match the acceleration force of the plane. It matches the forward speed of the plane, which provides a massively smaller acceleration, consequently a much smaller force, which is vastly overwhelmed by the plane acceleration. |
Ah ha! Yes! But to match that forward speed it also has to match the acceleration, otherwise how would it get up to that speed? |
But as we've already gone over multiple times, that acceleration only provides speed to the wheels, and a small component of backward force.
m isn't insignificant either, for a plane, even if there was perfect transfer, which there plainly isn't.
It has to match acceleration to match the speed. Not provide enough acceleration to match the force (which would mean the treadmill was moving much, much faster than the plane speed).
Message edited by author 2006-12-06 16:47:28.
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12/06/2006 04:47:44 PM · #158 |
Originally posted by jhonan:
Originally posted by hankk:
What is the speed of the plane relative to? What do we consider to have a speed of 0 MPH? |
An observer at the side of the runway. |
Assuming the observer is not on the treadmill-runway (I think that's what you meant) if the plane had a speed of 600 MPH going north, the treadmill would have a speed of 600 MPH going South.
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12/06/2006 04:48:54 PM · #159 |
Originally posted by Gordon:
Originally posted by sodoff:
What do you mean, incorrectly?? Surely this is basic science a 12 year old can understand?
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Do you have a rolling suitcase at home ? or a roller skate ? Or anything with wheels that do not provide thrust, but reduce friction ?
Spin those wheels. spin them faster. turn it upside down and just spin the wheel.
The rotation of the wheel does not drive the object. Often the speed is similar, but for example, if you held that suitcase on a treadmill, while the treadmill was moving - even very quickly, the speed of the wheels would not be matched by you accelerating the suitcase. You could also easily pull the suitcase forward, no matter how fast those wheels were spinning. |
This is going round and round, the same old argument. Everyone agrees that the the wheels do not produce thrust, that they provide friction. They are mere appendages.
But they do rotate at a speed that is in relation to the thrust/velocity of the engine. By matching that speed/thrust/velocity, the treadmill will actually provide the negative acceleration. This is Einstein's Theory, or do we all know more that him. |
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12/06/2006 04:51:46 PM · #160 |
Originally posted by hankk:
Originally posted by jhonan:
Originally posted by hankk:
What is the speed of the plane relative to? What do we consider to have a speed of 0 MPH? |
An observer at the side of the runway. |
Assuming the observer is not on the treadmill-runway (I think that's what you meant) if the plane had a speed of 600 MPH going north, the treadmill would have a speed of 600 MPH going South. |
Yes, sorry, that's what I meant. I assume the original vaguely-worded question implies that the treadmill's speed can adjust to make the plane appear stationary to an onlooker. |
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12/06/2006 04:51:57 PM · #161 |
Hey legalbeagle I bet you are having one hell of a belly laugh!
:-P |
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12/06/2006 04:52:26 PM · #162 |
The plane would clearly take off because it's thrust is against the air - although the plane wheels would be spinning faster then it would without the treadmill :-)
In the same vein - In a car doing 100km how fast is the bottom of the tyre going (the bottom been the part against the road)? |
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12/06/2006 04:53:01 PM · #163 |
Originally posted by sodoff:
But they do rotate at a speed that is in relation to the thrust/velocity of the engine. By matching that speed/thrust/velocity, the treadmill will actually provide the negative acceleration. This is Einstein's Theory, or do we all know more that him. |
You still assume that the speed of the wheels is somehow related to the speed of the plane. It normally is. It just doesn't have to be.
This goes back to Newton, you don't need to bring relativity in to it.
F=ma
The treadmill matches speed with the plane, and potentially thus accleration but certainly not forward force.
Fforward =m * a(from the jets)
Fbackward = whatever is transferred from the wheels to the plane, via the action of the treadmill on the wheels.
To keep the plane stationary, Fforward has to equal Fbackward
The plane and treadmill match speed and thus acceleration.
But that doesn't mean they match force, particularly as the wheels spin independently of the plane's forward motion. They might spin twice as fast, which would impart a slightly increased backward force, beyond the basics of friction. But certainly not enough to balance Fforward.
You can hypothetically accelerate the treadmill enough to balance those forces, but that would mean driving the treadmill at a much, much faster speed than the plane - which is not what was initially stated.
Message edited by author 2006-12-06 16:53:33.
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12/06/2006 04:53:12 PM · #164 |
Originally posted by Zal:
Originally posted by TomH1000:
Originally posted by Spazmo99:
Originally posted by Zal:
The "pro-takeoff" people are assuming that the plane will out-accelerate the treadmill, eventually achiive forward motion, and hence lift and takeoff. |
No, the treadmill will simply make the wheels spin faster, but it does nothing to retard the forward motion of the plane itself. |
You are correct. If the wheels were the power of thrust (like a car) then no, the plane would not fly but, since thrust is achieved by the turbine pushing against the air which is not in anyway tied to the treadmill the plane will fly. |
But an airplane needs LIFT to takeoff--it doesn't matter how THRUST is generated!!
The only way to generate LIFT is to have airflow over the wings, either by moving the airplane (accelerating down a runway) or by moving the air (wind tunnel where the plane is stationary).
Do we all agree that unless the airplane is physically moving, it will not take off? |
Yes the airplane must be moving but lets look at this a different way. Let̢۪s say the air is like a big brick wall just behind the planes engine but not connected to the treadmill. No matter how fast the treadmill moves in the opposite direction the plane will remain in the same place because of the brick wall even though the wheels are spinning. Apply thrust against this wall and the plane will move forward. Air is the same thing just not as hard as brick wall but if you apply thrust against it the plane will move forward.
Message edited by author 2006-12-06 16:56:44.
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12/06/2006 04:53:58 PM · #165 |
| Okay. Einstein was wrong. |
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12/06/2006 04:54:26 PM · #166 |
Originally posted by Gordon:
But as we've already gone over multiple times, that acceleration only provides speed to the wheels, and a small component of backward force.
m isn't insignificant either, for a plane, even if there was perfect transfer, which there plainly isn't.
It has to match acceleration to match the speed. Not provide enough acceleration to match the force (which would mean the treadmill was moving much, much faster than the plane speed). |
I think this is the best, most concise description of why the plane will move and thus take off. The treadmill will meet the requirement of same speed as per the riddle, but not even close to the same amount of force. |
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12/06/2006 04:54:38 PM · #167 |
Originally posted by jhonan:
Originally posted by hankk:
Originally posted by jhonan:
Originally posted by hankk:
What is the speed of the plane relative to? What do we consider to have a speed of 0 MPH? |
An observer at the side of the runway. |
Assuming the observer is not on the treadmill-runway (I think that's what you meant) if the plane had a speed of 600 MPH going north, the treadmill would have a speed of 600 MPH going South. |
Yes, sorry, that's what I meant. I assume the original vaguely-worded question implies that the treadmill's speed can adjust to make the plane appear stationary to an onlooker. |
It says pretty clearly that the plane speed and treadmill speed will be matched. Nothing more. Nothing about the plane being stationary.
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12/06/2006 04:55:57 PM · #168 |
Originally posted by sodoff:
Okay. Einstein was wrong. |
Which of Newton's basic principles do you think Einstein is violating here ? :)
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12/06/2006 04:56:27 PM · #169 |
This thread is really long and I admit I didn't read the whole thing but I have an example that will hopefully be helpful as to why the plane would take off - or rather that despite the treadmill the plane would make forward motion and then take off regardless of the treadmill...
If I have a model rocket (like the science experiment rockets kids use) and I am super strong and hold the rocket in the air horizontally and then light the fuse, the rocket will not move forward as long as I hold it - I am completely preventing it from moving forward. If I let go the rocket doesn't fall to the ground, it moves forward and flies because the force from the back is propelling it forward. It doesn't matter that it was initially stationary, it's the air pressure that moves it forward.
This would work if I held it out the window of a bullet train going the opposite direction too.
The point is, the plane wouldn't stay on the treadmill very long, it would move forward regardless of how fast the treadmill was going.
Another way to look at it is a model plane in a train. I can make a model plane take off inside of a train despite the fact that the train may be going the opposite direction of my plane. |
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12/06/2006 04:58:41 PM · #170 |
Correct my faulty assumptions on this please.
When planes take off it rolls down the tarmac only to create movement relative to the air.
Planes are designed to fly in the air.
If the air is moving past them fast enough, they fly, even if to an observer on the ground the plane seems to be standing still.
If the air and the plane are moving at the same speed the plane falls, even if to an observer on the ground the plane seems to be moving very fast.
The treadmill in the original question is there to eliminate the appearance of groundspeed, but does not counter any air speed the plane can generate.
Message edited by author 2006-12-06 17:03:25. |
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12/06/2006 05:01:58 PM · #171 |
Originally posted by Gordon:
The plane and treadmill match speed and thus acceleration.
But that doesn't mean they match force, particularly as the wheels spin independently of the plane's forward motion. They might spin twice as fast, which would impart a slightly increased backward force, beyond the basics of friction. But certainly not enough to balance Fforward.
You can hypothetically accelerate the treadmill enough to balance those forces, but that would mean driving the treadmill at a much, much faster speed than the plane - which is not what was initially stated. |
That was exactly my hypothetical argument - I had to break it down to physics...
I concede that given the word 'speed' and not 'force' is used in the original question then the plane will take off (leaving behind a smouldering wrecked treadmill) ;-) |
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12/06/2006 05:02:53 PM · #172 |
Originally posted by Megatherian:
Another way to look at it is a model plane in a train. I can make a model plane take off inside of a train despite the fact that the train may be going the opposite direction of my plane. |
Thats correct but remember that air in the train is also moving in the same direction as the train. So this is a little different here.
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12/06/2006 05:02:55 PM · #173 |
Originally posted by Gordon:
Originally posted by sodoff:
Okay. Einstein was wrong. |
Which of Newton's basic principles do you think Einstein is violating here ? :) |
Okay, so Newton...Einstein?? What am I, a genuis??
I know what I mean |
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12/06/2006 05:03:39 PM · #174 |
Originally posted by sodoff:
Originally posted by Gordon:
Originally posted by sodoff:
Okay. Einstein was wrong. |
Which of Newton's basic principles do you think Einstein is violating here ? :) |
Okay, so Newton...Einstein?? What am I, a genuis??
I know what I mean |
No fundamental physical principles are broken here. The plane takes off.
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12/06/2006 05:04:42 PM · #175 |
Originally posted by Gordon:
Originally posted by sodoff:
Originally posted by Gordon:
Originally posted by sodoff:
Okay. Einstein was wrong. |
Which of Newton's basic principles do you think Einstein is violating here ? :) |
Okay, so Newton...Einstein?? What am I, a genuis??
I know what I mean |
No fundamental physical principles are broken here. The plane takes off. |
Thank God for that. Every time you go the airport, it's bloody delayed!! |
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