Plane on a conveyor belt

What's Hot
1151618202128

Comments

  • SporkySporky Frets: 27580

    Word on the street seems to be that a loaded 747 should be able to hold on brakes, but if it's not loaded or it's slippy then it will slide.
    That gives us all a convenient 'out'.
    "[Sporky] brings a certain vibe and dignity to the forum."
    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
  • monquixotemonquixote Frets: 17485
    tFB Trader
    Maynehead said:
    Failure conditions of the tyres don't need to be considered as previously mentioned. 
    I was hoping you wouldn't notice that, as I'd already written it and couldn't be bothered deleting it  :3
    You can't leave a pedant that kind of opening :)
    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
  • Sporky said:
    Sporky said:
    PolarityMan said:the conveyer might itself be sitting on a truck which is driving backwards at a speed equal to the speed of the planes wheels.
    Or there might be a space-rabbit with laser eyes that will vapourise the plane if it even twitches.
    It might be dark.
    Space rabbit ain't scared of the dark.
    I meant that it wouldn't be able to see the plane. And before you point out that it has laser eyes we all know that a laser capable of destroying a jet would be outside the visible spectrum (obviously to think otherwise would make the whole premise absurd)
    ဈǝᴉʇsɐoʇǝsǝǝɥɔဪቌ
    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
  • MayneheadMaynehead Frets: 1782
    Sporky said:

    Word on the street seems to be that a loaded 747 should be able to hold on brakes, but if it's not loaded or it's slippy then it will slide.
    That gives us all a convenient 'out'.
    Unfortunately not, as the wheels would already be spinning at a considerable rate before traction is broken in monquixote's hypothesis and the coefficient of friction would be different (likely lower) than the static friction value under those circumstances.

    Still doesn't mean it can accelerate quickly enough to reach minimum takeoff speed before the runway runs out though :)
    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
  • monquixotemonquixote Frets: 17485
    tFB Trader
    Maynehead said:

    Still doesn't mean it can accelerate quickly enough to reach minimum takeoff speed before the runway runs out though :)
    Strictly speaking it doesn't have to as provided it can escape the conveyor belt it could taxi to an appropriate location and take off somewhere else.

    I realise this is massively going against the spirit of the question :)
    0reaction image LOL 0reaction image Wow! 1reaction image Wisdom
  • MayneheadMaynehead Frets: 1782
    Maynehead said:

    Still doesn't mean it can accelerate quickly enough to reach minimum takeoff speed before the runway runs out though :)
    Strictly speaking it doesn't have to as provided it can escape the conveyor belt it could taxi to an appropriate location and take off somewhere else.

    I realise this is massively going against the spirit of the question :)
    I do admire your imagination though  =)
    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
  • hywelghywelg Frets: 4302
    Drew_TNBD said:
    Sporky said:
    hywelg said:

    The movement of the plane is not governed by the rotation of its wheels
    Have you ever watched a plane take off? I can assure you that the wheels do rotate. If they didn't there'd be a horrible screeching noise and a lot of friction and then the tyres would burst or the landing gear would snap.

    If the movement of planes on the ground wasn't governed by their wheels then planes wouldn't have wheels.
    He meant to say the flight of the plane is not governed by the rotation of its wheels.
    No I didn't. I meant exactly what I said. The rotation of the wheels is a consequence of the aircraft moving forward. It's not governed by. 

    Jeez now people are losing the ability to understand English never mind maths and physics. 
    1reaction image LOL 0reaction image Wow! 0reaction image Wisdom
  • Emp_FabEmp_Fab Frets: 24209
    OK, so if we accept that in any non-wheel-speed-matching scenario, the plane takes off, what would happen in a wheel-speed-matching scenario ?  The plane engines start to produce thrust, and begins to move forward, the conveyor moves backwards at the same speed as the wheel rotation...  We know from Newton's laws (that cannot be ignored) that the plane has to move forward - so - it will move forward.  The forces on the plane guarantee that it absolutely must move forward.  To deny this is to deny Newton's laws of motion - which are immutable.

    So - the only possible explanation is that it is impossible somehow for the wheel speed to match the speed of the conveyor.  Something has to give - and it cannot be Newton's laws, so it has to be the other element in the equation.


    Lack of planning on your part does not constitute an emergency on mine.
    Also chips are "Plant-based" no matter how you cook them.
    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
  • MayneheadMaynehead Frets: 1782
    edited October 2016
    Emp_Fab said:
    OK, so if we accept that in any non-wheel-speed-matching scenario, the plane takes off, what would happen in a wheel-speed-matching scenario ?  The plane engines start to produce thrust, and begins to move forward, the conveyor moves backwards at the same speed as the wheel rotation...  We know from Newton's laws (that cannot be ignored) that the plane has to move forward - so - it will move forward.  The forces on the plane guarantee that it absolutely must move forward.  To deny this is to deny Newton's laws of motion - which are immutable.

    So - the only possible explanation is that it is impossible somehow for the wheel speed to match the speed of the conveyor.  Something has to give - and it cannot be Newton's laws, so it has to be the other element in the equation.


    In my very first post on the first page I had already answered this (and in fact a lot of the questions that arose later in the thread).

    The belt would speed up in an attempt to prevent the plane from travelling forwards, until such a point is reached where the friction generated by the speed of the belt travelling backwards precisely negates the thrust generated by the engines.

    Should such an equilibrium be unreachable, the belt will continue to speed up to infinite speed, at which point the thought experiment terminates, before the plane is allowed to take off (or even start to move).
    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
  • sinbaadisinbaadi Frets: 1297
    You might as well say that the entire conveyor belt moves without turning and the plane leaves it on the ground when it takes off.  The wheels can't turn at all.  Nothing would cause them to turn without the plane moving forward, which it can't.  

    Of course it can, but within the rules it can't.  Rather than think about take-off think about the initial moment.
    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
  • Emp_FabEmp_Fab Frets: 24209
    edited October 2016
    I think my head is about to explode.  I refuse to accept that a breach of Newton's laws is possible yet I also accept that no forward movement is possible with a wheel that moves at the same speed to a conveyor travelling in the opposite direction.
    Arrrrrrrggggghhhhhhh!!!!


    Lack of planning on your part does not constitute an emergency on mine.
    Also chips are "Plant-based" no matter how you cook them.
    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
  • monquixotemonquixote Frets: 17485
    tFB Trader
    Emp_Fab said:
    I think my head is about to explode.  I refuse to accept that a breach of Newton's laws is possible yet I also accept that no forward movement is possible with a wheel that moves at the same speed to a conveyor travelling in the opposite direction.
    Arrrrrrrggggghhhhhhh!!!!

    Why do you think Newton's laws are being breached?
    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
  • Emp_FabEmp_Fab Frets: 24209
    I didn't say I thought they were being breached.  I specifically said I refuse to believe they could be.
    Lack of planning on your part does not constitute an emergency on mine.
    Also chips are "Plant-based" no matter how you cook them.
    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
  • monquixotemonquixote Frets: 17485
    tFB Trader
    Emp_Fab said:
    I didn't say I thought they were being breached.  I specifically said I refuse to believe they could be.
    To rephrase.

    What bit are you struggling with?
    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
  • hywelghywelg Frets: 4302
    OK lets simplify this.

    Drag race car on the start line (rear wheel drive obvs). Needs to maximise traction so applies the front brakes and spins the rear wheels to warm up the tyres. Car goes nowhere

    So what speed are the wheels doing. Obviously the front wheels are moving at zero velocity. Are the rear wheels moving ?

    No of course not. They are rotating, not the same as moving. They have zero velocity. They are however able to rotate whilst not moving. In this case its because they lost traction. In the case of the aircraft its because theres a moving conveyor under them. At no point do the aircraft wheels lose traction therefore their peripheral speed is identical to the speed of the conveyor. However the velocity of the wheel, (at the axle relative to the ground), can be different to both the peripheral speed (i.e. the rotational speed) and the conveyor speed.


    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
  • SambostarSambostar Frets: 8745


    Backdoor Children Of The Sock
    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
  • NomadNomad Frets: 549

    Forgive the repetition...

    Nomad said:

    What is the 'opposite direction' in this context? If the plane is on a normal runway and facing to the left, and if we followed the wheels with our eyes, they would rotate anti-clockwise - the top of the wheel would move left, and the bottom of the wheel (on the tarmac) would move right.

    If we add in the conveyor, how does it move? Is the idea that it counteracts the rotation of the wheels? If so, would that mean that the conveyor moves to the left to counteract the right-moving bottom of the wheel that it's in contact with?




    Nomad
    Nobody loves me but my mother... and she could be jivin' too...

    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
  • SambostarSambostar Frets: 8745


    Warren

    Backdoor Children Of The Sock
    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
  • Emp_FabEmp_Fab Frets: 24209
    Emp_Fab said:
    I didn't say I thought they were being breached.  I specifically said I refuse to believe they could be.
    To rephrase.

    What bit are you struggling with?
    The fact that Newton's third law means the plane must move yet the conundrum condition of the wheel speed matching the conveyor speed means that no forward motion is possible.  
    Lack of planning on your part does not constitute an emergency on mine.
    Also chips are "Plant-based" no matter how you cook them.
    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
  • monquixotemonquixote Frets: 17485
    tFB Trader
    Emp_Fab said:
    Emp_Fab said:
    I didn't say I thought they were being breached.  I specifically said I refuse to believe they could be.
    To rephrase.

    What bit are you struggling with?
    The fact that Newton's third law means the plane must move yet the conundrum condition of the wheel speed matching the conveyor speed means that no forward motion is possible.  
    If it moves the experiment becomes invalid so that's one outcome. If it doesn't then it has to be because all of the energy is being dissipated through the wheel bearings and tires. In either case no laws need to be broken.
    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
Sign In or Register to comment.