Plane on a conveyor belt

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  • SambostarSambostar Frets: 8745
    edited October 2016


    Edit: These musings of a drunk man are irrelevant to the question.

    Backdoor Children Of The Sock
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  • HAL9000HAL9000 Frets: 9551
    edited October 2016
    Emp_Fab said:
    ...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.  
    Exactly this. The problem contains an irresolvable contradiction - Newton says the aircraft must move; the conveyor, as described, means that aircraft can't move. Since both can't be true the question is paradoxical and cannot be solved. 

    I play guitar because I enjoy it rather than because I’m any good at it
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  • SambostarSambostar Frets: 8745
    Everyone always relies on someone else to some up with the equation and then quotes it as their own.
    Backdoor Children Of The Sock
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  • SporkySporky Frets: 27576
    Emp_Fab said:

    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.  
    That's why I've been saying it's a paradox. The two can't be resolved.

    Much like the question of what happens if an irresistible force meets an immovable object - the answer is that you can't have a universe that allows both to exist. Thus the question is a philosophical one, not a physics one.
    "[Sporky] brings a certain vibe and dignity to the forum."
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  • Emp_FabEmp_Fab Frets: 24209
    edited October 2016
    It cannot be a philosophical one alone.  It is possible to physically build the setup described.  What I need to understand is what actually happens when you conduct the experiment.  Something will happen...  the plane doesn't shrug its wings, light up a Gauloises and say "Zis experiment ees a paradox, I cannot exist".  

    If someone can explain in terms of forces and Newtonian physics what actually happens to the plane and the thrust when you match the wheel speed with the conveyor speed, then I'll be happy.  Dismissing it as 'a paradox' is avoiding the answer.
    Lack of planning on your part does not constitute an emergency on mine.
    Also chips are "Plant-based" no matter how you cook them.
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  • SambostarSambostar Frets: 8745
    edited October 2016




    But at the end of the day, the wheels are going faster than the treadmill, which the question states cannot happen.  Despite whatever forces are at play.  So yeah, it'll take off, but you haven't read the question.



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  • monquixotemonquixote Frets: 17485
    tFB Trader
    Emp_Fab said:
    It cannot be a philosophical one alone.  It is possible to physically build the setup described.  What I need to understand is what actually happens when you conduct the experiment.  Something will happen...  the plane doesn't shrug its wings, light up a Gauloises and say "Zis experiment ees a paradox, I cannot exist".  

    If someone can explain in terms of forces and Newtonian physics what actually happens to the plane and the thrust when you match the wheel speed with the conveyor speed, then I'll be happy.  Dismissing it as 'a paradox' is avoiding the answer.
    If you really built it the plane would take of and the conditions of the question would be violated. The conclusion is it's a silly question.
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  • SporkySporky Frets: 27576
    Emp_Fab said:
    It cannot be a philosophical one alone.  It is possible to physically build the setup described. 
    I don't think you can build it to match the constraint that the conveyor matches the speed of the wheels, unless you guarantee that the engines don't turn on, which also violates the set-up.

    Emp_Fab said:

    If someone can explain in terms of forces and Newtonian physics what actually happens to the plane and the thrust when you match the wheel speed with the conveyor speed, then I'll be happy.  Dismissing it as 'a paradox' is avoiding the answer.
    I don't think it can be described in those terms, because the setup doesn't allow for Newtonian physics to function. But I will try.

    1. Plane's engines fire.
    2. Pilot increases thrust just enough to break the stixion (sp?)in the wheel system.
    3. At this point the thrust from the engines should move the plane forward, so the wheels start to roll.
    4. The conveyor instantly matches the speed of the wheels, so the plane doesn't move.
    5. The thrust from the engines should still move the plane forwards, so the wheels start to roll faster.
    6. Goto 4.
    7. The conveyor therefore instantly reaches relativistic speeds trying to achieve 4, which requires infinite force and energy (impossible) otherwise the plane and thus wheels would move faster than the conveyor, which isn't allowed.
    8. The conveyor and wheels turn into plasma, destroying the whole setup.

    That's the problem - the conveyor is impossible, and this becomes apparent if you put a plane or wheeled rocket or jetcar or propellor-driven car or a trolley you push from alongside onto it. If you put something with driven wheels on it'd all seem fine.
    "[Sporky] brings a certain vibe and dignity to the forum."
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  • Emp_FabEmp_Fab Frets: 24209
    AAHHH !!!  Right.... so the key to it all is that the thrust needed to keep the plane stationary remains the same, regardless of belt speed.  In a real-world scenario, the pilot would increase the throttles a little bit and the plane would start to move forward, the belt operator would match the speed.  At that point, the thrust is set to match the rolling friction of the wheel bearings.  Increasing the thrust further will result in the plane moving forward - further increases in belt speed will have zero effect on the plane's movement (as demonstrated in your video).  Once you have enough thrust to overcome the wheel bearing friction, that's it - anything more will make the plane move forward (and thus takeoff), anything less will result in the plane moving backwards, BUT - the speed of the belt is utterly irrelevant.

    Therefore in a conundrum where the belt matches the plane's speed, the plane moves forward and takes off.
    In a conundrum where the belt is supposed to match the wheel's speed, the plane still moves forward and takes off - because - there is only one throttle setting at which the plane's thrust matches the friction of the wheels - and that results in the plane remaining stationary, regardless of belt speed.  If the pilot increases the throttles, the plane moves forward (thus temporarily breaking the rule) and the belt operator increases the speed of the belt to match, but the whee.....  SHIT SHIT SHIT SHIT SHIT !!!!!!   I almost had it !!!

    angry annoyed frustrated rage fuck me
    Lack of planning on your part does not constitute an emergency on mine.
    Also chips are "Plant-based" no matter how you cook them.
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  • Emp_Fab said:
    AAHHH !!!  Right.... so the key to it all is that the thrust needed to keep the plane stationary remains the same, regardless of belt speed.  In a real-world scenario, the pilot would increase the throttles a little bit and the plane would start to move forward, the belt operator would match the speed.  At that point, the thrust is set to match the rolling friction of the wheel bearings.  Increasing the thrust further will result in the plane moving forward - further increases in belt speed will have zero effect on the plane's movement (as demonstrated in your video).  Once you have enough thrust to overcome the wheel bearing friction, that's it - anything more will make the plane move forward (and thus takeoff), anything less will result in the plane moving backwards, BUT - the speed of the belt is utterly irrelevant.

    Therefore in a conundrum where the belt matches the plane's speed, the plane moves forward and takes off.
    In a conundrum where the belt is supposed to match the wheel's speed, the plane still moves forward and takes off - because - there is only one throttle setting at which the plane's thrust matches the friction of the wheels - and that results in the plane remaining stationary, regardless of belt speed.  If the pilot increases the throttles, the plane moves forward (thus temporarily breaking the rule) and the belt operator increases the speed of the belt to match, but the whee.....  SHIT SHIT SHIT SHIT SHIT !!!!!!   I almost had it !!!

    angry annoyed frustrated rage fuck me
    This would be a great post if the riddle was "prove confirmation bias exists".
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  • SporkySporky Frets: 27576
    Emp_Fab said:

    Therefore in a conundrum where the belt matches the plane's speed, the plane moves forward and takes off.
    Yes!

    Emp_Fab said:

    In a conundrum where the belt is supposed to match the wheel's speed, the plane still moves forward and takes off - because - there is only one throttle setting at which the plane's thrust matches the friction of the wheels - and that results in the plane remaining stationary, regardless of belt speed.  If the pilot increases the throttles, the plane moves forward (thus temporarily breaking the rule) and the belt operator increases the speed of the belt to match, but the whee.....  SHIT SHIT SHIT SHIT SHIT !!!!!!   I almost had it !!!
    Sort-of yes.

    Either the belt never moves, which is impossible if the engines fire, or it instantly accelerates to infinite speed, which is just downright impossible, or it doesn't match the speed of the wheels, which isn't allowed by the question.

    Thus the belt isn't possible. The question isn't possible. That's why your attempts to analyse it from a Newtonian-physics point of view hasn't worked. It's not that the physics is wrong, it's that the setup of the scenario is wrong.

    "[Sporky] brings a certain vibe and dignity to the forum."
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  • Emp_FabEmp_Fab Frets: 24209
    edited October 2016
    No... that's not true!!!  If I stick a real plane on a real conveyor and start the engines, the plane will move, the belt will move backwards.  Once the thrust is set so it matches the rolling resistance, everything is in equilibrium - the wheels and belt are synchronised and the plane remains stationary.  If I increase the speed of the belt, the plane remains stationary* and the wheels and belt are still in sync. (*that's the hard bit to get your head around until you watch Monquixote's video).  If I increase the thrust on the plane, the plane moves forward - which means the speed of the wheels is greater than the speed of the belt, so......  I'VE GOT IT !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!    In the conundrum where the wheels are to match the conveyor's speed, the plane will not take off because there is only a small window where the wheel and belt speeds can be in sync - and that is from zero to the speed where the thrust equals the rolling resistance. (Edit: actually, that's incorrect; there is only one point where the thrust cancels out the rolling resistance.  Thrust less than this results in the plane moving backwards, thrust greater - forwards).  Increasing the belt speed beyond this point results in the plane's wheels spinning faster (and still in sync with the belt) but no movement of the plane, and no airflow.  Increasing the thrust on the plane results in the plane moving forward and taking off, but at the cost of the synchronisation with the belt.

    What do I get as a prize ?
    Lack of planning on your part does not constitute an emergency on mine.
    Also chips are "Plant-based" no matter how you cook them.
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  • Actually I was wrong.
    Another experiment you can do at home.
    Take a matchbox car tie a string to it with a weight at the end.
    Let the weight hang over the table.
    Place the car on a mat. Leave the mat stationary the car will move. Now pull on the mat forward (opposite direction to the travel of the rotation of the wheels) The car will still drag its way forward but the wheels will most likely slip.
    Pull the mat backwards and the car will still travel forward.
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  • hywelghywelg Frets: 4302
    Sporky said:
    4. The conveyor instantly matches the speed of the wheels, so the plane doesn't move.

    That's where logic left you.

     How can the conveyor slow the aircraft down?  It can only influence the rotation of the wheels.

    I thought we had agreed that this has to be s frictionless scenario otherwise it all falls apart (there is no conveyor belt that can support the weight if a jet in a point loading).  Therefore the movement of the conveyor can impart no equal reaction in the aircraft. 

    So the conveyor stating up only has the inertia of the wheels rotation to overcome it cannot move the aircraft and hence the wheels spin faster, though they still only move at the same speed as the aircraft.  
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  • Drew_TNBDDrew_TNBD Frets: 22445
    13 pages...

    This is why none of you are musicians.
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  • SporkySporky Frets: 27576
    hywelg said

    That's where logic left you.

     How can the conveyor slow the aircraft down?  It can only influence the rotation of the wheels.

    How many times now have I explained that it is a paradox?

    Yes, no conveyor can slow the plane down. However, the question states that the conveyor matches the speed of the wheels, but in the opposite direction.Thus the setup of the scenario precludes the plane's wheels, and thus the plane, from moving.

    However, this is clearly impossible. The scenario is impossible because it prevents the plane from moving via a method which could not, in the real world, prevent the plane from moving.

    Paradox.
    "[Sporky] brings a certain vibe and dignity to the forum."
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  • SporkySporky Frets: 27576
    Drew_TNBD said:
    13 pages...

    This is why none of you are musicians.
    Logical fallacy on the grounds of a faulty premise.
    "[Sporky] brings a certain vibe and dignity to the forum."
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  • NomadNomad Frets: 549
    Sporky said:

    ...the question states that the conveyor matches the speed of the wheels, but in the opposite direction.


    Opposite direction of what?

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

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  • SporkySporky Frets: 27576
    Nomad said:
    Sporky said:

    ...the question states that the conveyor matches the speed of the wheels, but in the opposite direction.


    Opposite direction of what?

    What does it say in the question?
    "[Sporky] brings a certain vibe and dignity to the forum."
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  • Drew_TNBDDrew_TNBD Frets: 22445
    Sporky said:
    Drew_TNBD said:
    13 pages...

    This is why none of you are musicians.
    Logical fallacy on the grounds of a faulty premise.
    Did you leave your sense of humour at church this morning?
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