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  1. Join Date
    Jul 2005
    Posts
    199
    #91
    Quote Originally Posted by mbeige View Post
    But it is stated that in the question, the conveyor belt matches the speed in the opposite direction! How many times will I say that? Read the original question!
    naku! hindi pa pala tapos ito.

    ok am gonna say it again..."imposible yun"...just like my previous example..if you are going to pull a table cloth from underneath a plate or a glass without toppling or moving it, you have to pull it quickly. right?...try doing pulling it slowly and chances are the plate or glass will move together with the table cloth...malinaw ba yun? what is your conclusion therefore? the faster the movement of the cloth the more chances the plate will stay in place... the darn plate dont even have wheels!!!

    now, how are you gonna keep a plane from moving forward, move the conveyor slowly?

    the problem is we were given a wrong premise that it is possible...you accept that premise most likely your answer/conclusion will also be wrong..agree?

    "the conveyor will match the speed of the plane, instantly"... jeez! you believe that?! what do i think? if i'm going to believe what you guys are saying that the plane would be stationary then the conveyor would not even move! why? e di kayo narin dapat sumagot...remember its the plane's speed that we are talking about and not the rotation/movement of the wheels.

    again, the plane's wheels are not powered, they will only move if the plane will move..and also in this case if the tarmac/conveyor will move...they have nothing to do with the plane's propulsion..given enough thrust the plane will move forward with or without wheels (sira nga lang underbelly/fuselage )...some hydro planes dont have wheels hehe! (joke!) (here you can use artificial wave making machine instead of conveyor belt )

    my conclusion:

    1. the plane will be able to take-off.
    2. indeed its very easy to make things complicated...its genius to make them simple.
    3. salvaje si otep..hehehe!

  2. Join Date
    Aug 2006
    Posts
    636
    #92
    nahilo ako sa mga response...wala namang ganung runway di ba? na isahan naman tayo ni doc...

  3. Join Date
    Oct 2002
    Posts
    2,703
    #93
    Quote Originally Posted by Alpha_One View Post
    Ah, your FBD is incomplete and your analysis is completely wrong.
    Let's see your FBD then.
    Major flaw: The runway friction and engine thrust spin the wheels in the SAME direction, not in opposite directions. Try mo pa sa matchbox on a tablecloth. The only opposing force acting on the wheels is the friction of the wheelbearings, which is constant (unlike engine thrust) as well as negligible.
    The forces shown on the FBD are accurately depicting their directions and where they are applied.

    Obviuosly, Fb, being off-center, produces torque which tends to rotate the wheel. Friction force is always against motion, if the wheel tends to move forward with Ff, then Fb will try to oppose it.

    The friction on the wheel bearing is basically negligible and because of this, the wheel is allowed to rotate. When the wheel rotates, it will move forward (and the plane flies) IF the runway is not moving. With a moving runway, the forward motion of the wheel is exactly opposed, hence the wheel, although rotating, stays in place.

    In the FBD, a moving runway is depicted as Fb being significant to oppose Ff. If Fb is made greater than Ff, then the wheel/plane would be moving backward! (meaning, the conveyor/runway was adjusted too fast!)

    The wheel bearing, with almost zero friction, actually plays an important role of the wheel. It is its frictionless property that allows the wheel to move along the road. But with a moving runway, it is also its frictionless property that allows the wheel to stay in place while rotating.
    We're not concerned about forces acting on the wheels, we consider the forces acting on the plane itself. The big force acting against the plane is wind resistance, not friction from the ground. Remember, the wheels are designed to freewheel.
    The wheel is attached to the plane. If it moves, the plane moves. Sure you can have an FBD of the plane, and it will show the same forces. There will be Fb that will oppose Ff. There is no wind resistance when the plane is stationary or just starting to move.
    It's not the runway that's frictionless, it's the wheel bearings as far as this problem is concerned.
    Yes, its the wheel bearing that is frictionless. It does simulate a frictionless runway in the case of non-moving runway. If the runway is frictionless, the plane can take off with a ski, instead of wheels, and it would not matter if the runway is moving or not.

    If the wheel bearings got stuck, the plane will not move if the runway does not move; the plane will move backwards with a moving runway (even if the engines are at full thrust).
    Again, runway speed = plane speed (for the nth bloody time) does NOT imply runway force ACTING ON THE PLANE = engine thrust.
    Then let's see your FBD so you could clarify what "runway speed = plane speed" would imply.

  4. Join Date
    Oct 2002
    Posts
    19,438
    #94
    i stand by my answer that the plane WILL NOT TAKE OFF.

    the jet engine is just like a vacuum cleaner upfront. it sucks in air, which means all the air will go straight into the turbine and NOT PASS UNDER THE WINGS which CREATES THE LIFT necessary for the airplane to take off.

  5. Join Date
    Oct 2002
    Posts
    10,620
    #95
    Quote Originally Posted by niky View Post
    AGH!!!! HINDI KAYO NAGBABASA!!!!


    [size=4]FORGET THAT THE PLANE HAS TO FLY. THE QUESTION IS, CAN IT MOVE FORWARD AGAINST THE CONVEYOR?[/size]
    pare with all due respect look at the TOPIC...

    Will the Airplane Fly?????????

    me take... it will move forward (a bit) pero surely it will not fly...

  6. Join Date
    Oct 2002
    Posts
    9,894
    #96
    :headache:

  7. Join Date
    Aug 2004
    Posts
    22,710
    #97
    Quote Originally Posted by kimpOy View Post
    pare with all due respect look at the TOPIC...

    Will the Airplane Fly?????????

    me take... it will move forward (a bit) pero surely it will not fly...
    Okay, read my post again.

    Now, go buy a torque wrench, a matchbox car, and find an electric treadmill.

    I will do this experiment myself when I have the time, and I will film it for all of you.

    [size=4]For the treadmill to keep the plane from moving forward, it must exert x force on the plane, where x is directly proportional to the speed of the plane and treadmill.[/size]

    Thus, for every y mph FASTER the treadmill goes, it must exert x times y amount of force on the airplane to keep it from moving forward and thus, achieving take-off speed.

    But you'll find, with your handy-dandy torque wrench (hell, if you can't buy one, get a hanging weighing scale from the wet-market, and tie it to the car), that the force exerted by the treadmill on a wheeled vehicle is not related to the speed of the treadmill in a linear fashion.

    [size=4]It will exert roughly the same amount of force on the wheeled vehicle at 1 mph or 100 mph.[/size]

    I'm sorry... this is getting seriously silly. All of you go out NOW and find a treadmill and a weighing scale. Then come back and apologize. :hysterical:

    [size=1]OTEP!!! May utang ka nang beer sa akin!!!!!!!!!![/size]

    Ang pagbalik ng comeback...

  8. Join Date
    Oct 2002
    Posts
    1,496
    #98
    di nyo naman nililinaw e.

    ano ba brand ng airplane?

  9. Join Date
    Dec 2003
    Posts
    11,317
    #99

  10. Join Date
    Aug 2004
    Posts
    22,710
    #100
    *Kinyo: wheel speed does NOT equal airplane speed.

    The airplane is not wheel driven. The wheels can be moving 1000 mph along the conveyor, and the plane will still be going at the same speed it would be going if the wheels were moving at 50.

    Your analogy on the wheel plane thing is false.

    If the wheel moves, the plane moves, right?

    If the runway moves, does the wheel move? NO. The Wheel is not attached to the runway.

    [size=4]This is the tablecloth trick. The tablecloth is the runway, the wheeled plane is a plate on the table. Pull the runway out from under the plane fast enough, and it won't move.[/size]

    Now do you understand?

    Ang pagbalik ng comeback...

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Will the Airplane Fly??????????