I've asked you this several times with no answer..... what is it about the treadmill's motion, that is going to prevent or even deter, forward motion of the plane?
Plane on a Treadmill
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I've asked you this several times with no answer..... what is it about the treadmill's motion, that is going to prevent or even deter, forward motion of the plane?
First the obvious-but-wrong answer. The unwary tend to reason by analogy to a car on a conveyor belt--if the conveyor moves backward at the same rate that the car's wheels rotate forward, the net result is that the car remains stationary. An aircraft in the same situation, they figure, would stay planted on the ground, since there'd be no air rushing over the wings to give it lift. But of course cars and planes don't work the same way. A car's wheels are its means of propulsion--they push the road backwards (relatively speaking), and the car moves forward. In contrast, a plane's wheels aren't motorized; their purpose is to reduce friction during takeoff (and add it, by braking, when landing). What gets a plane moving are its propellers or jet turbines, which shove the air backward and thereby impel the plane forward. What the wheels, conveyor belt, etc, are up to is largely irrelevant. Let me repeat: Once the pilot fires up the engines, the plane moves forward at pretty much the usual speed relative to the ground--and more importantly the air--regardless of how fast the conveyor belt is moving backward. This generates lift on the wings, and the plane takes off. All the conveyor belt does is, as you correctly conclude, make the plane's wheels spin madly.
A thought experiment commonly cited in discussions of this question is to imagine you're standing on a health-club treadmill in rollerblades while holding a rope attached to the wall in front of you. The treadmill starts; simultaneously you begin to haul in the rope. Although you'll have to overcome some initial friction tugging you backward, in short order you'll be able to pull yourself forward easily.
As you point out, one problem here is the wording of the question. Your version straightforwardly states that the conveyor moves backward at the same rate that the plane moves forward. If the plane's forward speed is 100 miles per hour, the conveyor rolls 100 MPH backward, and the wheels rotate at 200 MPH. Assuming you've got Indy-car-quality tires and wheel bearings, no problem. However, some versions put matters this way: "The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation." This language leads to a paradox: If the plane moves forward at 5 MPH, then its wheels will do likewise, and the treadmill will go 5 MPH backward. But if the treadmill is going 5 MPH backward, then the wheels are really turning 10 MPH forward. But if the wheels are going 10 MPH forward . . . Soon the foolish have persuaded themselves that the treadmill must operate at infinite speed. Nonsense. The question thus stated asks the impossible -- simply put, that A = A + 5 -- and so cannot be framed in this way. Everything clear now? Maybe not. But believe this: The plane takes off.
A thought experiment commonly cited in discussions of this question is to imagine you're standing on a health-club treadmill in rollerblades while holding a rope attached to the wall in front of you. The treadmill starts; simultaneously you begin to haul in the rope. Although you'll have to overcome some initial friction tugging you backward, in short order you'll be able to pull yourself forward easily.
As you point out, one problem here is the wording of the question. Your version straightforwardly states that the conveyor moves backward at the same rate that the plane moves forward. If the plane's forward speed is 100 miles per hour, the conveyor rolls 100 MPH backward, and the wheels rotate at 200 MPH. Assuming you've got Indy-car-quality tires and wheel bearings, no problem. However, some versions put matters this way: "The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation." This language leads to a paradox: If the plane moves forward at 5 MPH, then its wheels will do likewise, and the treadmill will go 5 MPH backward. But if the treadmill is going 5 MPH backward, then the wheels are really turning 10 MPH forward. But if the wheels are going 10 MPH forward . . . Soon the foolish have persuaded themselves that the treadmill must operate at infinite speed. Nonsense. The question thus stated asks the impossible -- simply put, that A = A + 5 -- and so cannot be framed in this way. Everything clear now? Maybe not. But believe this: The plane takes off.
Best post ever... This had me laughing... It's like Plane-on-a treadmill-anonymous...
It's okay... I thought the same thing at first too... but if you read a little about it it does make sense...
I predict that ever day a new person will jump into this thread... say it won't fly, and then 100 posts later they will believe it too.
So... by say the end of the year... and 100,000 posts from now, everyone on the board will believe....
The belt is moving at exactly the same speed as the plane, in the opposite direction. EVERY example around the internet has this included, that the belt is set up to always move at the same speed of the plane but in the opposite direction, so when the plane speeds up, the belt also speeds up. The plane is NEVER moving forward relative to a non-moving reference point.
Let me ask this.
Plane is on a treadmill -engines are off, treadmill is doing 30 MPH. Plane moves backwards, right?
Plane is on a treadmill, engines are ON and idling at a low thrust - say enough for a typical taxi speed of 10MPH, treadmill is still doing 50MPH. And for good measure, the treadmill is accelerating 1 MPH for every marked change in engine thrust from that would increase plane foward velocity 1MPH to get from stationary to 10MPH
Is all this math and phyics trying to tell me that the plane would still move forward?
Plane is on a treadmill -engines are off, treadmill is doing 30 MPH. Plane moves backwards, right?
Plane is on a treadmill, engines are ON and idling at a low thrust - say enough for a typical taxi speed of 10MPH, treadmill is still doing 50MPH. And for good measure, the treadmill is accelerating 1 MPH for every marked change in engine thrust from that would increase plane foward velocity 1MPH to get from stationary to 10MPH
Is all this math and phyics trying to tell me that the plane would still move forward?
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IF that small amount of thrust is able to overcome the static friction, then the plane will move forward at ~10mph.
That doesn't really answer my question. Since the wheels are free-wheeling..... HOW does the motion of the treamill prevent forward motion of the plane. Please explain HOW the treadmill would do this.
You might want to Google a few more sites. I did just now and the top few all concluded that it would take off, no matter what the treamill was doing.
If the treadmill belt is moving as fast as the plane in the opposite direction, how then can the plane move forward on the treadmill?
Yes it would move forward... it doesn't have to overcome the speed of the treadmill, just the tiny amount of friction between the wheels and the bearings...
This is just plain wrong.
You clearly do not yet understand the relationship of the wheels to the plane, is different than on a wheel driven car. Please read the long post above with the bar-code signature and then ponder for a while before responding. I think if you carefully think about this, you will understand that the plane will take off NO MATTER WHAT the treadmill is doing.
The motion of the treadmill is essentially MEANINGLESS in this whole debate. It's a distraction to fool you, and fool you (and many others) it did.
I've been saying for a long time now that I misjudged the intent of the question. The trick question.
If you still want a bone to pick, I can debate the laws of physics all day long.
Are you saying that even if the plane is not moving forward on the treadmill it will still fly?
If you run on a treadmill, you are running the same speed that the treadmill is going, not double it, if you run faster you move forward on the treadmill, be it ever so slightly, I am not following that if the plane is on the treadmill how it will be moving forward, of course if it is moving faster than the treadmill it will take off, but what about when the plane remains stationary. I do not believe any air will be moving over the wings, am I right on this?
Do you understand that a planes wheels are different than a car? If a plane was moving at 30mph and the treadmill also at 30mph in the opposite direction, the plane would still move forward at 30mph, but the wheels would spin at 60mph.
Second, the problem, on this very site, post #1, says the treadmill MATCHES the speed of the plane. BUT, that does not mean it negates the speed of the plane, since the wheels are free spinning they can accelerate and decelerate independently of the speed of the plane.
We have given many real world examples that are easier to comprehend then the thought of a plane on a treadmill, and all of them show that the plane would move forward. Toy car on a treadmill, shopping cart on a treadmill, person in rollerblades on a treadmill. They all show how the object on the treadmill would move forward in this situation.
Thrust...... it's the same thing that moves the plane forward whether it is on the treadmill or not. Thrust.
It has nothing to do with the wheels.
Now, I have answered your question.... answer mine. HOW is the treadmill's movement acting on the plane to prevent its movement? HOW???
I apologize, I had forgotten our late night discussion last night. Please don't start discussing physics, we all know how you feel about friction :wink:
The way I see it - and I don't really understand the math or physics of this at all - is that it's a bit of a trick question. Probably more of an uneducated one.
IMO - the intent of a tradmill is to negate foward motion. probably 95% of the public would think this could be accomplished, even with a plane and the right equipment.
However what most of these guys are saying is that it's darn near impossible to build such a treamill that could move at such speeds to maintain the necessary friction to offset all the trust of a plane. No matter how fast that thing is spinning - the plane is going to be able to offset that and move forward.
So the way I see it, the myth isn't proven or busted - it just can't really happen.
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Herbi, you thought the same as htown at one time, maybe you can convince him because we obviously are not getting through to him!
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