Originally posted by Sam The ShamThis is an old puzzle and there have been a zillion threads exactly like this. I think someone came up with a formula for how threads on this topic would go which is pretty accurate.
Airplane ain't pushing on any air if it ain't moving through it. It won't take off. For the wings to provide lift it must have velocity relative to the air mass around it. It's so obvious. Engines provide THRUST, not lift. (Well, they do provide a little lift from the air they move over the wings, but it's infinitesimal) The air moving across the wing s ...[text shortened]... ent to full power before the plane started moving.
And the question is poorly worded.
This thread shows that I once thought like you but it turns out I was wrong.
http://www.playtheimmortalgame.com/board/showthread.php?threadid=54537&page=2
Originally posted by Sam The ShamTo save you tons of reading (or save you from reading the previous posts in this thread);
Airplane ain't pushing on any air if it ain't moving through it. It won't take off. For the wings to provide lift it must have velocity relative to the air mass around it. It's so obvious. Engines provide THRUST, not lift. (Well, they do provide a little lift from the air they move over the wings, but it's infinitesimal) The air moving across the wing s ...[text shortened]... ent to full power before the plane started moving.
And the question is poorly worded.
As soon as the engines start working the airplane will move forward, relative to the ground. At that point the conveyor does nothing but make the wheels spin faster. The wheels are not driven by the engine, but rotate freely.
The plane will thus move in the air, resulting in the needed lift to take off.
Originally posted by duecerThe point of the question is to realise that a treadmill CANNOT slow a plane down like it slows a car down. Therefore the plane does NOT remain stationary, it moves and takes off almost exactly as though it were on a normal concrete runway.
If the plane remains stationary relative to the ground it cannot fly.
People blather on about how it's a badly worded question but if you realise that a treadmill cannot slow a plane down it becomes trivial.
Originally posted by TheMaster37Oh hell.......you're right. The way the question is worded gives the impression that the plane isn't moving because of the treadmill, but it is, the wheels would just spin faster.
To save you tons of reading (or save you from reading the previous posts in this thread);
As soon as the engines start working the airplane will move forward, relative to the ground. At that point the conveyor does nothing but make the wheels spin faster. The wheels are not driven by the engine, but rotate freely.
The plane will thus move in the air, resulting in the needed lift to take off.
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Originally posted by tomtom232"If a plane is traveling at takeoff speed on a conveyor belt, and the belt is matching that speed in the opposite direction, can the plane take off?"
you are missing the point! How can the plane be travelling at any speed if there is no driving force? And if the plane is travelling a simple force diagram will show you that the plane has to be moving relative to the ground because it pushes on the air not the tread mill.
Sigh. One more time.
Physics minded folks (myself) know that ALL speed is relative. In _my_ opinion, this sentence implies that the speed the plane is "traveling" is relative to the "tread mill" (as you put it) and not necessarily the ground. The very use of the word "tread mill", which is something my wife uses daily in the morning, implies that the user of that tread mill is stationary to the ground but not to the belt on the tread mill!
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Originally posted by MarsanNot really. If you said "very long moving runway" or "infinitely long conveyor", I'd understand that the plane can "move" along that "tread mill".
People blather on about how it's a badly worded question but if you realise that a treadmill cannot slow a plane down it becomes trivial.
But since you said "tread mill" (which usually conjures up, you know, an exercise tread mill), these things are scarcely 4 ft long. At that point you have to kinda assume the plane stays ON the tread mill don't you?
If I were to try that on my wife's treadmill, I GUARANTEE you the plane would not take off prior to falling off the edge of the tread mill.
So NO, the plane won't take off on a treadmill.
And if you still don't think this is poorly worded. Type "tread mill" into Google and tell me what you see.
Originally posted by SickboyFinally, Adam and Jamie carefully navigate their way through a myth that has baffled everyone from web bloggers to pilots. If a plane is traveling at takeoff speed on a conveyor belt, and the belt is matching that speed in the opposite direction, can the plane take off? Extensive small-scale testing with a super treadmill and a nearly uncontrollable model airplane don't completely resolve the myth, so our flight cadets supersize the myth with help from a willing pilot and his Ultralight flying machine
Not really. If you said "very long moving runway" or "infinitely long conveyor", I'd understand that the plane can "move" along that "tread mill".
But since you said "tread mill" (which usually conjures up, you know, an exercise [b]tread mill), these things are scarcely 4 ft long. At that point you have to kinda assume the plane stays ON the tread m this is poorly worded. Type "tread mill" into Google and tell me what you see.[/b]
this is the original question. As you can see when it does use treadmill it say "super treadmill" and there is nothing about taking off on the conveyor belt the question asks "can" the plane take off.
Like I said its just ignorance that makes people want to blame the wording of the question.
Originally posted by Sickboyyou seem ignorant to me not physics minded and anyways most people no intuitively that speed is relative that is why the word "faster" was created.
"If a plane is traveling at takeoff speed on a conveyor belt, and the belt is matching that speed in the opposite direction, can the plane take off?"
Sigh. One more time.
Physics minded folks (myself) know that ALL speed is relative. In _my_ opinion, this sentence implies that the speed the plane is "traveling" is relative to the "tread mill" ...[text shortened]... ad mill is stationary to the ground [b]but not to the belt on the tread mill![/b]
surely when you read the question common sense tells you that
we are not investigating the possibility of the 2130 from London to New York attempting to take off from noting more than the exercise machine from your local gym! The term treadmill is used to allow any reader to get an instant grasp of the problem being posed. As to the answer: It took me a while to fully get it, I spent a bit of time seeing both sides of the argument and never seeing why one was right and one wrong! However now I do understand I have come up with an analogy that i have found useful when explaining it to a few of my colleges. I will adapt it for those of you still considering the use of your wifes treadmill, this will allow you to try things for yourself!!!
Take the treadmill and set it up on an incline. If you have a fancy one, you can do this will the hill climb setting, otherwise prop a book up under the front end.
Switch the treadmill on
Take a toy car and hold it on the treadmill at the top of the incline
The movement of the treadmills belt will be rotating the wheels of the car
let go of the car
does it stay still, travel up the incline with the belt or roll down the incline against the movement of the belt?
take the same principal and apply to the airplane take off problem. Replace the gravitational force that moved the toy car with the force of the planes jet engines.
Originally posted by 3DDBeautiful analogy, makes everything crystal clear.
[Take the treadmill and set it up on an incline. If you have a fancy one, you can do this will the hill climb setting, otherwise prop a book up under the front end.
Switch the treadmill on
Take a toy car and hold it on the treadmill at the top of the incline
The movement of the treadmills belt will be rotating the wheels of the car
let go of the car
does it ...[text shortened]... Replace the gravitational force that moved the toy car with the force of the planes jet engines.[/b]
I have found this a fascinating thread, not so much because of the question, which is interesting in itself, but because of the difficulty many have had believing the well written solution. It is an interesting test case of paradigms, which parallels many of the blunders we face in the game of chess. If you can't visualize the solution it is very hard to comprehend the true answer.
It'd be funny if Adam and Jamie end up enlisting the aid of English professors and lawyers to solve this rather than scientists and engineers. After all, the controversy surrounding this myth is really about semantics and not so much physics.
Could be the most boring Myth-busters episode ever.
Wow - crazy discussion.
I guess the way I see it is this:
The forward movement of the plane is dependant on the propulsion of the engines, which are only minorly influenced by the treadmill. I agree that if a plane's forward momentum relied totally on the wheels alone, then we would have an issue.
The wheels would cause a form of drag - Agreed. This is temporary based on inertia. Once the wheels are spinning, the amount of energy required to keep the plane in place is minimal because the inertial energy in the wheels is already spent. *they're already spinning* which then means that any additional thrust would be put towards the momentum of the plane.
I could see this causing a problem if the brakes were on on the wheels. Then you have a more permanant form of drag... but this is just my 2c.
I'm interested to see how it turns out :-)