Brain Teaser

Discussion in 'Off Topic' started by csmguitarman, Oct 25, 2007.

  1. piranah

    piranah New Member

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    Thats a Sox fan for ya. Kidding. I didnt say I didnt like the debatable part, but I was pointing out that it is a debatable question. Yes if the engines are burning, they will propel the plane forward,
    but the op also says that it is moving at the same rate of speed as the plane, so thus if the engines were burning, the treadmill will be going the same speed ( in theory). i gotta stop reading my econ book. too much thinking.
  2. csmguitarman

    csmguitarman New Member

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    the plane will move forward no different than if it were on regular ground. try to think of yourself on a treadmill wearing rollerblades. Say i am going to stand behind you but off the treadmill and push you at 10mph forward. So now we will turn the treadmill on to ten mph. I PUSH. you move forward up the treadmill at 10mph and the treadmill is moving at 10mph opposite. the wheels are moving at 20mph. I am a force independent of the contact of the wheels to the treadmill. Same with the plane only the jets sucking in and spewing out air is a force independent of the wheels to the runway.

    So when i am saying is the the plane will accelerate down the runway at normal speed until it reaches take off speed.
  3. MBK2

    MBK2 New Member

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    Well your OP sounded as if the speed of the plane's wheels and the speed of the treadmill would be the same, and increasing when the jets engines try to push the plane forward with it's thrust. So if the plane starts rolling up to 20 mph, so would the treadmill, thus keeping the plane at the same exact spot.

    If you said the plane starts rolling at 10 mph and the treadmill is set at 10 mph, and the treadmill's speed wouldn't increase...then you have a case..but that's not the way your original question was made to sound.

    The plane isn't floating, it is contacting the treadmill with it's enormous weight.

    BTW, if you wore rollerblades and I pushed you at 10 mph and the treadmill was set to 10 mph...you'd stay at the exact same spot, regardless of my push because I'm also walking at 10 mph while pushing you. Now if you said that my force would eventually increase your speed, while the treadmill's speed stayed the same..... then that's another story....
  4. Der Alta

    Der Alta New Member

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    Lets see if I can expand a bit more on this.

    Example #1. We put a 100hp car on the conveyor belt. You step on gas, the car stay stationary. As much as you accelerate, the belt keeps pace. Thus, the car goes not move. Agree?

    Example #2. Same car, except pit crew has added Mucho Modifications to the engine, drive train, transmission and even added a spoiler to the rear of the car to create downforce. You now have 900hp. You step on the gas and the car accelerates. The belt keeps pace, the car stay stationary. Agree?

    Example #2a. The Spoiler on the rear of the car generates no down force, because the car is not moving. No movement = no air to push on the wing. Ergo No downforce is generated. Agree?

    Example #3. Same car, except the Pit Crew has bolted a Solid Fuel Rocket Booster to the roof. They hand you the Big Red Trigger to start the booster. 900 Hp + 15,000 lbs of thrust. Car is in Park with E-Brake set. Tires will not turn. You hit the trigger, car moves down the conveyor belt. Tires get ripped to shreds as they get dragged across the conveyor belt which is moving in the opposite direction at the same speed. Agree?

    Example #4. Same car, same Booster except car is turned off, in Neutral with no E-Brake. You hit the trigger, car moves down the conveyer belt, tires no longer getting shredded. Conveyor belt spins wildly to work in opposition to the speed of the car, not the force of the Booster. Agreed?

    Example #5. Pit crew removes Booster and bolts an Engine and Propeller to hood of car. Car in Park, E-Brake set. Propeller forces air over car, Spoiler on rear of car has air movement across it, Downforce is generated. Car does not move. Agreed?

    Example #6. You release E-Brake. Propeller pulls car forward, Conveyor belt and tires spin wildly at same speed. Car still moves forward, because the propeller is pulling the car through the air. Agreed?

    Example #7. Pit crew bolts wings onto car. E-Brake is not set, car is in Neutral. Propeller cranks up, pulls car forward, conveyor belt spins wildly, you gain enough speed to get airborne. You subsequently are given a Darwin award for bolting an engine and wings onto a car with no directional ability, and flying it into the trees at the end of the runway. Agreed?
  5. MBK2

    MBK2 New Member

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    Not sure what you're trying to say Der Alta, but #6 is false already.
    The plane is not 'floating' thru the air to allow the jet engine or propeller to pull it other than on the ground. Thus as the propeller or jet engine builds it's thrust the plane starts rolling forward, but the conveyor belt below is going in the opposite direction at the same speed generated by the tires...the plane stays stationary...thus no lift can be happening....right?

    So #7 doesn't even apply...right??

    I mean I can understand if the plane is free floating to begin with, but it's not. Gravity has it firmly compressed to the ground (or the treadmill in this case), No forward momentum, no opportunity for any lift to render the plane light enough to start floating, thus having no consequential contact with the treadmill. :tounge:
  6. Der Alta

    Der Alta New Member

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    So you agree with me up through #5. In that statement, you acknowledge that the air is being moved by the propellor and downforce is being generated by the air across the spoiler. Correct?

    In that statement, you have to acknowledge that the E-Brake and Park is holding the car from moving. The car not moving = the treadmill not moving. We agree? If you agree that the air is generating downforce across the spoiler it means there is force being applied to the E-Brake. If the Air is being forced rearward, it must be counteracted by something to stop forward movement. Newton's 3rd law applies. Any Force must have an equal force in the opposite direction.

    For instance, I'm standing on pavement and to move, I must push against the ground, and the ground returns that force. Ergo, I move forward. Same situation on Ice, except the ice returns no push (Coefficient of friction is considerably less than asphalt) and as such, I don't move.

    OK, so back to the Air being pushed rearward. The air is being pushed rearward, because the propellor is trying to pull the car forward. Since e-Brake is on and car is in park, thus the tires are locked from moving, the air is forced backward. The only opposing force to that rearward force is the tires on the conveyor belt. The locked tires prevent the car from moving forward. Do we agree up to this point?

    Now what happens when you drop the car into neutral, and release the E-Brake? Does the conveyor start to spin before or after the tires do?

    Now lets take a look at another example. A Plane in Flight at 5000 feet up. How does it stay up in the air? Easy, the air movement under/over the wings, creates lift. How does the air get moved over/under the wings? It doesn't. The air is stationary, and the propeller pulls the wings through the air mass. The Lift is generated because the propeller pulls them through the air.

    The biggest piece of information you need to realize, is since the wheels are free-wheeling, it follows that the conveyor belt, no matter how fast it is moving, CANNOT EXERT ANY FORCE on the aircraft [SIZE=-1]with respect to forward motion! There is no force in our experiment that can oppose the thrust vector of the aircraft.[/SIZE]

    Once you accept that the conveyor belt can only match the speed of the tires and not prevent motion, you'll see that the plane will indeed move forward.

    As for gravity, yes, the plane is sitting on the ground. But that is a vertical force, not a horizontal force. Gravity will not counteract the horizontal movement.

    Perhaps another conceptual example. You hit a high fly to left field. The ball goes in two directions. "Up" and "Away". The only thing to slow down the "Up" is Gravity. Gravity will not interact with "Away". Friction due to the Air will counteract the "Away". Nothing will slow that ball down until it either hits the ground or Air Friction. Not enough "Up" and grounds out to the shortstop. Not enough "Away" and it lands in the Catchers mitt. Much like in a vaccum, a Feather and a Penny fall at the same rate of speed.

    This demonstrates the Air is a solid force and the Propeller interacts with it to pull the plane forward. The wheels of the plane can't stop this forward movement, nor can the conveyor belt. The conveyor belt only interacts with the wheel and vice versa, in a vertical application, not a horizontal.

    A swimmer pulls himself through the water, like the propeller will pull the plane through the air.
  7. MBK2

    MBK2 New Member

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    I'm sorry Der Alta but the pure physics of this is being dismissed.
    I don't agree with any of your analogies just because you say 'agreed' at the end.

    If the brakes are applied how do you propose the car moves forward??...By floating on air?

    There was a plane (can't remeber the name) which had thrust downward, thus creating a hover, that was the only way the plane could take off, because of the hovering effect.
    But the propeller or the jet thrust is rearward and not counteracting the forces of gravity. So if the conveyor belt matches the speed the the forward thrust that is being generated, the plane stays stationary....no 'lift' to get the plane airborne.

    I could understand if the conveyor belt stays at the same speed, then eventually the jets thrust would outrun the belt, but the question is made to think that the conveyor belt matches the forward speed...again I say forward speed, not upward.

    If what you're saying is true, then a jet or prop plane need merely rev their jet engine or propeller while sitting still, then just let go and take off.

    Sorry, it doesn't work that way. forward speed creates the airflow underneath the wings which creates the lift to get the planes airborne. If the plane is stationary, then no more lift, the plane can't take off.

    :tounge:
  8. csmguitarman

    csmguitarman New Member

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    Alrighty MBK2 do a little internet research on this topic. Do you think i would ask a question to which i didnt know an answer. Your should be trying to understand why you are wrong not fight against it.

    PLANES FLY THROUGH AIR. a plane would not be able to fly in the air if you believed that the treadmill could prevent it from moving forward. Planes speed are measured in air speed not ground speed. The speed of a plane when it is in the air is not measure buy how fast the wheels are spinning. It is measure by how fast the plane is moving through the air. Same when it is one the ground the wheels are just there to prevent it from scraping the ground.

    Ask yourself, how can the treadmill match the planes speed. Well first the plane would have to be moving. Since there is no drive system for the wheels something else must move the plane. THE JETS. the only reason the the wheels turn is because something else is making the plane move. If the treadmill actually held the plane in place then the plane would be traveling at zero mph. and the treadmill would be too and the wheels would be to. the only way to make the treadmill turn is when it is matching the speed of the plane. The plane can only have "speed" if it is moving forward. On a runway that is not a treadmill the plane doesnt moving because the wheels are spinning, the wheels spin because the plane is moving.
  9. MBK2

    MBK2 New Member

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    You've been reading too much urban myths over the web...LOL :tounge:

    In order for the plane to utilize lift to get airborne, the plane has to travel along the runway to generate enough speed to create enough 'AIRFLOW' over and under the wings to create that lift.

    If the plane starts rolling 5 mph forward, the treadmill goes in the opposite direction at 5 mph, the plane stays in place doesn't it? If the plane's engine creates more forward thrust and then gets the plane rolling 20 mph, the treadmill also gets up to 20 mph in the opposite direction, thus the plane is still in the same exact spot isn't it??

    Where's the airflow coming from to give the plane the lift to be able to take off???

    BTW, the plane flys thru air 'AFTER' it generates enough speed to get the airflow over and under its wings to create the lift to be able to take off.
    Once airborne and with enough forward thrust from the engines, then what you're thinking would apply.
  10. csmguitarman

    csmguitarman New Member

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    you are answering your own question. how can the plane be traveling at 5 mph and at the same time stay in its place. again i ask....how does a plane move period....by pulling its self through the air. its is only when it pulls it self through the air fast enough that the wings take over for flight.
  11. MBK2

    MBK2 New Member

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    You mention that a planes wheels has no drivetrain, thus your theaory must be right....well if a car is in neutral and I push the car from behind, it's basically the same thing isn't it??

    So if I push that car that's in neutral and it starts going 1, 5, 10, 20 mph...AND...the treadmill matches that speed in the opposite direction....wouldn't I be in the same spot???
  12. MBK2

    MBK2 New Member

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    The planes wheels are rotating at 5 mph forward and the treadmill is turning in the opposite direction at 5 mph......the planes speed is 'ZERO' .

    The plane gets pushed/pulled thru the air 'ONLY' after it is airborne. While the plane is on the ground, it gets pushed/pulled on the ground...on it's wheels...

    I can't understand how you can't grasp that?? Unless you are trying to say that the planes wheels will eventually outrun the treadmill...:tounge:
  13. csmguitarman

    csmguitarman New Member

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    what make the plane wheels turn normally on the ground. the plane moving forward. THERE IS NOT DRIVE SYSTEM ATTACHED TO THE WHEELS. IF THE PLANES WHEELS WERE MOVING AT 5 MPH ITS IS BECAUSE THE PLANE ITS SELF IS MOVING FORWARD AT 5MPH. SO YOU ARE TELLING ME THAT A PLANE IS CAR WITH WINGS.
    why would a car not fly if it had wings. because once it had enough speed to lift off it would fall right back down to the ground because nothing would provide forward movement. a car must be in contact with the ground to accelerate. a plane must be in contact with air to accelerate.
  14. csmguitarman

    csmguitarman New Member

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    you again are answering your own questions. planes on the ground move on their wheels NOT BY THEM. they roll on wheels. the wheels do not provide acceleration on the ground they allow it

    please stop arguing and just try and understand. again this is all over the internet do some research
  15. MBK2

    MBK2 New Member

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    A car can fly if you design it like a jet-fighter and put wings and a jet engine on it.

    Again I ask you...If a plane's engine tries to thrust it forward at 500 mph...it has to roll along the ground/treadmill first, but the treadmill starts turning at 500 mph, how is the plane going to move forward??

    So if a plane is put on the waters edge, on a treadmill, 20 yards from it, you put the engines at full throttle forward...will it take off before it sinks?? If what you're trying to say is valid...it would be able to lift off without any forward movement...no?
  16. MBK2

    MBK2 New Member

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    Stop arguing?? It's OK for you to though?? All over the internet?? Where's the physics proof of what you're trying to say?? You're just going on urban myth that others are putting out over the net.
  17. MBK2

    MBK2 New Member

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    But if the treadmill is going in the opposite direction, matching the wheels rotation speed, how's the plane going to accelerate?? It's like a car burning rubber. If it has so much power that the tires just spin in place, the car does not move forward.

    You're stumbling yourself by bringing the treadmill scenario into the mix. You're trying to say that the planes engines will allow the plane to 'FLOAT' over the treadmill regardless of it's wheels contact on that treadmill.
  18. MBK2

    MBK2 New Member

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    One last question to be posed to you.

    I understand what you've been reading over the net. Yhey are trying to say that if the plane jet propullsion builds up enough, that's what makes the plane take off and not it's forward momentum on the runway creating lift with the wings.

    OK...The plane has no wheels....It is harnessed in place by an enormous chain which keeps it in place,,,the planes jet engine whirls like mad, creating an enormous amount of airflow thru it's turbines.....you suddenly release the harness...will the plane simply take off??...or will it still require forward movement to create the lift on the wings??
  19. csmguitarman

    csmguitarman New Member

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    No they are not. They are saying that the plane will roll down the treadmill runway like normal. How can the treadmill match the planes speed if it is stationary. the wheels dont just move on their own. On a normal runway the wheels only move because they are in contact with the ground not because there is some drive system hooked to them.

    answer this question if a plane is traveling down a runway and the second half of the runway it covered in ice does it stop accelerating once it is on the ice
    http://images.google.com/imgres?imgurl=http://meignorant.com/2posts/Fly-NotFly.gif&imgrefurl=http://meignorant.com/&h=210&w=420&sz=144&hl=en&start=2&tbnid=mQoT-LwHRSBy1M:&tbnh=63&tbnw=125&prev=/images%3Fq%3Dplane%2Btreadmill%26svnum%3D10%26hl%3Den%26safe%3Doff
    http://video.google.com/videoplay?d...=11&start=0&num=10&so=0&type=search&plindex=0

    please watch and learn. the first one watch the video halfway down.
  20. csmguitarman

    csmguitarman New Member

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    ok
    1. then it would be what we call a plane not a car
    2. if the engines trust forward at 500mph the the plane would be moving at 500moh. when a plane is in the air at 500mph do you think the wheels are spinning at 500mph? um no. and why not because there is nothing stationary touching them like the ground for example.

    so you are saying that the space shuttle that has over 40 million horse power could simply be held back from movement by a treadmill

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