Aircraft and conveyor belt (again)
- Thread starter Observer
- Start date
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No amount of you describing the question as defective, will deflect from the fact that its only defective if the plane does not move forward.
It is your assumption that this is correct.
You seem to ignore the fact that the plane MUST move forward and KEEP moving forward to keep the conveyor moving......
Sorry johnD, but the above statement shows that you do not understand.
Tell me what you do not understand about the following statement....
The plane MUST MOVE FORWARD to create wheel speed that the conveyor responds to.
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The question states that "This conveyor belt has a control system that tracks the aircraft's wheels speed and tunes the speed of the conveyor belt to be exactly the same as the wheels, but in the opposite direction."
If the wheels and the conveyor are going at exactly the same speed but in opposite directions, the plane must be standing still. The statement cannot be true if the plane is moving.
The question describes conditions that cannot exist except if the plane is staionary..
As Kevnurse said, it is like the rolling road where your car goes for its MOT to test the brakes. The wheels and the rollers move at exactly the same speed but in opposite directions, so the car stays still.
Do you disagree?
If the wheels and the conveyor are going at exactly the same speed but in opposite directions, the plane must be standing still. The statement cannot be true if the plane is moving.
The question describes conditions that cannot exist except if the plane is staionary..
As Kevnurse said, it is like the rolling road where your car goes for its MOT to test the brakes. The wheels and the rollers move at exactly the same speed but in opposite directions, so the car stays still.
Do you disagree?
I don't know why you think this is such a revelation, or why you need to overstate it.
The 'impossible question' situation was spotted by Observer, back on page 1, and the conclusion of infinite wheel speed also appeared on page 1.
We're now on page 10, and the argument hasn't moved forward. Much like the plane.
Either the OP (chilluk) in the original topic meant the question to be impossible, or he/she didn't mean it.
If he didn't mean it, then he clearly meant that the conveyor matches the aircraft speed, as a test of people's understanding of the forces that propel an aircraft to its take off speed. If anyone doesn't think that the plane will take off given this interpretation of the question, then that's where the debate should be going.
However, if he meant it to be impossible, then that's the end of the argument. Problem solved. Last one out please turn out the lights.
The rolling road scenario isn't the same thing at all simply because the thrust on the RR is applied relative to the RR and the thrust applied to the aircraft isn't.
To prove this, next time your car is on the rolling road John give it a shove from behind and watch what happens ... Or, attach a tow rope to the front and pull the car with another.
Then come back and tell us all
MW
To prove this, next time your car is on the rolling road John give it a shove from behind and watch what happens ... Or, attach a tow rope to the front and pull the car with another.
Then come back and tell us all
MW
yes, I know about the thrust. But the way the question is written, is as if the person writing it thinks an aircraft is driven by its wheels.
the equal and oposite speed thing works for a driven-wheel vehicle, and results in the vehicle staying stationary. It cannot be true for a vehicle that is moving.
It doesn't make sense applied to a thrust-propelled vehicle with undriven wheels.
If the vehicle is moving, propelled by thrust, then it is impossible for the wheels and the belt to be moving at equal but opposite speeds.
the equal and oposite speed thing works for a driven-wheel vehicle, and results in the vehicle staying stationary. It cannot be true for a vehicle that is moving.
It doesn't make sense applied to a thrust-propelled vehicle with undriven wheels.
If the vehicle is moving, propelled by thrust, then it is impossible for the wheels and the belt to be moving at equal but opposite speeds.
Errrrmmmm ... Why?
I read the OP to mean ...
The aircraft starts moving which starts the wheels turning, the system picks up the wheel motion and moves the conveyor belt to provide an equal but opposite turning motion.
Aircraft still moves forward relative to the ground either side of the conveyor though and takes off as normal.
Job's a good'un as far as I'm concerned.
MW
If the conveyor belt was static, and the plane started to move forwards at 1mph, the conveyor would detect the movement of the wheels and start to move at 1mph the other way. However thrust is still propelleing the plane forward at 1mph.
So now the conveyor is travelling backwards at 1mph, the plane is moving forwards at 1mph, so the wheel are turning at 2mph (at circumference).
But the rules in the question say the conveyor will turn at the same speed as the wheels, but in the opposite direction.
So the conveyor speeds up to 2 mph to match the wheels.
But the plane continues to travel forward at 1mph (it has very poor acceleration!) so the wheels are now spinning at 3mph.
It is impossible, at the same time, for the plane to be moving, and the conveyor to match the speed of the wheels.
The forward speed of the plane must be equal to the forward speed of the wheels minus the backward speed of the conveyor.
The rules in the question cannot be met unless the plane is stationary.
Of course, if you change the question to say what you think it ought to say, you can come up with a solution to match the re-worded question.
So now the conveyor is travelling backwards at 1mph, the plane is moving forwards at 1mph, so the wheel are turning at 2mph (at circumference).
But the rules in the question say the conveyor will turn at the same speed as the wheels, but in the opposite direction.
So the conveyor speeds up to 2 mph to match the wheels.
But the plane continues to travel forward at 1mph (it has very poor acceleration!) so the wheels are now spinning at 3mph.
It is impossible, at the same time, for the plane to be moving, and the conveyor to match the speed of the wheels.
The forward speed of the plane must be equal to the forward speed of the wheels minus the backward speed of the conveyor.
The rules in the question cannot be met unless the plane is stationary.
Of course, if you change the question to say what you think it ought to say, you can come up with a solution to match the re-worded question.
Equally, if your understanding of the problem matched mine and others who do not see it as you do then we'd all be in agreement.
Can't waste any more time trying to convince you, early start in the morning.
Bye bye.
MW
johnD......I think at the end of the day, it all depends on which angle you approach this question from, and the interpretation of the question.
I see merit in some of your points, but I still err on the side of the plane taking off.
Perhaps we should have a Poll...........................
I see merit in some of your points, but I still err on the side of the plane taking off.
Perhaps we should have a Poll...........................
Who said they didn't see a paradox?
JohnD. I completely agree that the wording of the OP prevents the aircraft from moving forward and I have thought this from the beginning. However since words can't lock an aircraft on the spot with the engines pushing when the wheels are free to turn, I've tried to put a practical slant on my thoughts. I've allowed a bit of give without trying to reword the OP.
Food for thought:
Every action has an equal and opposite reaction. e.g. You push against a soild wall and it pushes back with equal force. The wall behaves as if it is tuned to match the force you apply. Although the wall doesn't appear to move, it must do so in order to react. The runway surface is pushing upwards to support the aircraft and it is also pushing back against the lateral force trying to move the aircraft. Even before the aircraft begins to move, it is applying a lateral force to the runway and the runway is pushing back. Most people would consider all of this paragraph to be nonsense.
A tyre rolling along a surface will experience a minute amount of slippage in the direction it is travelling. If the tyre is being pushed by the vehicle it will rotate slightly slower than the speed of the vehicle. If it were propelling the vehicle it would travel slightly faster. There is a bit of give here, although again, most people would consider this to be nonsense.
JohnD. I completely agree that the wording of the OP prevents the aircraft from moving forward and I have thought this from the beginning. However since words can't lock an aircraft on the spot with the engines pushing when the wheels are free to turn, I've tried to put a practical slant on my thoughts. I've allowed a bit of give without trying to reword the OP.
Food for thought:
Every action has an equal and opposite reaction. e.g. You push against a soild wall and it pushes back with equal force. The wall behaves as if it is tuned to match the force you apply. Although the wall doesn't appear to move, it must do so in order to react. The runway surface is pushing upwards to support the aircraft and it is also pushing back against the lateral force trying to move the aircraft. Even before the aircraft begins to move, it is applying a lateral force to the runway and the runway is pushing back. Most people would consider all of this paragraph to be nonsense.
A tyre rolling along a surface will experience a minute amount of slippage in the direction it is travelling. If the tyre is being pushed by the vehicle it will rotate slightly slower than the speed of the vehicle. If it were propelling the vehicle it would travel slightly faster. There is a bit of give here, although again, most people would consider this to be nonsense.
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