Long rod question

Jonny69 said:
It's this if it doesn't stretch. What's the plane on a treadmill thing then?
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A plane is standing on a runway that can move (like a giant conveyor belt). This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).

Will the plane be able to take off?

Ma'am said:
I was thinking more along the lines of - what's the point of a 10 mile long rod ;)
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Bragging rights and the ability to wave it about in johnny foreigners face, because he can't have one.
 
Le_Petit_Lapin said:
A plane is standing on a runway that can move (like a giant conveyor belt). This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).

Will the plane be able to take off?
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Of course it will. The plane is creating pressure from it's jets or props against the air, not the runway. If the runway is moving it will just spin the planes landing wheels and if the wheels are locked in place then something will break! The plane wouldn't just sit there in any case. A car would though with speeds matched exactly.
 
Dr.EM said:
Of course it will. The plane is creating pressure from it's jets or props against the air, not the runway. If the runway is moving it will just spin the planes landing wheels and if the wheels are locked in place then something will break! The plane wouldn't just sit there in any case. A car would though with speeds matched exactly.
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You're wrong.

Please, let's not do this AGAIN.
 
I can see no other reasoning for this problem, it's pretty simple tbh. It's not like the plane no longer creates forward thrust when flying at altitude far away from any solid boundaries, this much is clear if you've even seen a plane flying! So what would possibly prevent it taking off?
 
A plane must have a certain speed to create enough force off the wings to take off. The engines to start with just push the plane forwards, they do not create lift. If all the forward momentum is taken up and negated by the moving runway then no lift will be created on the wings and the plane will never take off.
 
I'm suprised they even bothered to prove it. It's a bit far fetched to believe otherwise, it's like saying "you pick me up and i'll pick you up and then we'll be levitating" :D
 
Dureth said:
If all the forward momentum is taken up and negated by the moving runway then no lift will be created on the wings and the plane will never take off.
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And how is this done? Are we talking about the scenario where the plane is basically permanently fixed to the runway or the literal sense of an actual plane with landing wheels parked on a runway? I was thinking the latter which WILL take off. In fact in the latter all that will happen is the wheels will turn twice as fast.
 
In the given scenario the rod will move instantaneously. In the real world the rod will bend and create a wave which will travel down the rod like a slinky.
 
Le_Petit_Lapin said:
Can we forget about the plane? It takes off.

Only posted it here because Jonny69 wanted to know what the question was.
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Whilst i agree that thread has been and gone and shouldn't be repeated here again, it's hard to just let it go when people state as fact (like you have) something that is simply wrong...
 
A Level physics and my degree tells me that an aeroplane produces thrust, accelerating the aeroplane because of a force off the rotating blades and expelled mass and from its engines in a rearward direction. The wheels are not connected to this in any way other than they produce a small amount of friction, a small force in the opposite direction to the engines. You'd have to wind that treadmill up pretty damn fast for that frictional force in the wheel bearings to equal the force produced by the thrust of the engines.
 
Dureth said:
A plane must have a certain speed to create enough force off the wings to take off. The engines to start with just push the plane forwards, they do not create lift. If all the forward momentum is taken up and negated by the moving runway then no lift will be created on the wings and the plane will never take off.
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using your terms in the right way.

the engines push the plane forwards
going forwards creates lift
the lift makes the plain take off as easily as on tarmac (if you dont count small friction in bearings

the conveyor belt cannot stop or reduce any of those forces (unless the plane has its brakes locked on)


just think of the planes that fly and land from water



and the rod moves instantly if its has ZERO stretch and friction
 
Grrrrr said:
Whilst i agree that thread has been and gone and shouldn't be repeated here again, it's hard to just let it go when people state as fact (like you have) something that is simply wrong...
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IT TAKES OFF.

The wheels just keep spinning faster and faster. The plane requires no friction against the ground in order to take off. Think of a seaplane.
 
Grrrrr said:
Whilst i agree that thread has been and gone and shouldn't be repeated here again, it's hard to just let it go when people state as fact (like you have) something that is simply wrong...
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errrrrrrrrrrr

how on earth does the plane NOT take off then if thats what your saying ? you are doing exactly what you say you hate :/
 
So with the rod scenario it's decided that in thoery it would move instantly but in the real world no material is hard/dense enough to support this? Presumably diamond would be at the top though rather than any metals, kinda pricey though :p
 
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