since we all know exactly what is going to happen, why don't we put a wager on this.

i'll handle the 5% betting fee.

1/29/2008 4:30:01 PM

I don't care what you or anyone else argues.

I only care what I argue.

And I've been right.

The entire time.

1/29/2008 4:30:03 PM

Quote :

"If the raw speed of the belt = speed of the plane, then relative to the earth, it is not moving. where does the lift come from? Until the plane is moving sufficiently fast enough relative to the earth/air, it cannot take off. "

bobby...this is where i believe you are misunderstood...the treadmill moves at a speed counter to the speed of the plane, and this is the kicker, as referenced by the ground/air, not the speed its traveling on the treadmill. the reason this can be stated is because the original question posed asked if the plane could take off. under full throttle and since it takes minimal thrust to overcome the frictional forces due to the wheel bearings, the plane does move forward relative to the ground/air around it. get it?

1/29/2008 4:30:48 PM

unless the ground is moving and the air isn't

Quote :

"I only care what I argue. And I've been right. The entire time."

you sound like someone I know, the kicker is, if you argue something that's wrong to begin with are you ever right?

[Edited on January 29, 2008 at 4:32 PM. Reason : f]

1/29/2008 4:31:15 PM

i just want to see half of you lose.

1/29/2008 4:31:16 PM

Quote :

"If the raw speed of the belt = speed of the plane, then relative to the earth, it is not moving. where does the lift come from?"

the point is, once turn on the plane's engines which provide thrust against to the air around the plane, then then raw speed of belt, which is relative to the earth around the plane, is irrelevant.

when you add thrust, this equation:
"the raw speed of the belt = speed of the plane"
is no longer valid or physically possible. Adding "If" to the beginning of it does not make it a true or valid.

1/29/2008 4:31:42 PM

so let me get this straight. the plane is essentially spinning its wheels on the treadmill? staying stationary in relation to all points along the tread mill support system?

1/29/2008 4:33:39 PM

lets just make this clear....the speed of the plane that the treadmill matches is the speed as observed by a bystander on the ground, not on the treadmill!!

1/29/2008 4:35:35 PM

Quote :

"3) Now in the "real world scenario". There is surface friction between the wheels and the belt, and there is some friction between the wheels and the axles. This would play out almost exactly as in scenario #2, however a little bit of the thrust of the engines would be required to equalize the friction caused by the spinning wheels. In this real world case, if the plane was sitting there, and the belt started to move slowly backwards, it would stand to reason that the plane would start to move backwards with it. However, if the engines were turned on a little bit, they would overcome the friction between the wheels and the axles. As you learned in Statics and Dynamics, i'm sure, there is a difference between Static Friction and Rolling Friction, so once the engines provide enough trust to overcome the Static Friction between the wheels and the axles, the wheels will start to spin. Then the thrust can be decreased, and to keep the plane in the same place the thrust only has to match the drag created by the Rolling Friction. If the belt starts to spin faster, then maybe the engines have to compensate a bit, but just enough to match the Rolling Friction so the plane stays in one place. Once these forces are equalized, as soon as the engines are throttled up a little more, then the plane will start to move forward, and after that it will play out just like in scenario 1 and 2."

1/29/2008 4:36:26 PM

Quote :

"bobby...this is where i believe you are misunderstood...the treadmill moves at a speed counter to the speed of the plane, and this is the kicker, as referenced by the ground/air, not the speed its traveling on the treadmill. the reason this can be stated is because the original question posed asked if the plane could take off. under full throttle and since it takes minimal thrust to overcome the frictional forces due to the wheel bearings, the plane does move forward relative to the ground/air around it. get it?"

Ok, where IS the original question? All of this hinges on assumptions. As I read it from this thread, the assumption is that the treadmill and plane are exerting respective forces such that the plane is motionless relative to the earth.

In which case, no take off

If the plane is moving fast enough relative to the earth because the thrust overcomes the force of the treadmill, of course it'll take off.

1/29/2008 4:37:12 PM

Quote :

"Unless there is wind, speed relative to the air or ground is the same."

if the plane is on a damned moving treadmill, then the speed relative to the air and ground most certainly is not the same. That's why the treadmill could be moving at 100mph beneath the plane (i.e. the "ground speed" of the plane) but relative to the air it wouldn't be moving, and therefore obviously not producing any lift on the wings.

Under normal circumstances, on a normal runway in a normal airport, with no wind, yes, obviously the ground speed = air speed as the plane goes down the runway.

But the whole fucking point of this exercise that that the ground is moving, so the exercise comes down to if it is the ground speed or air speed that is important for the plane to take off.

1/29/2008 4:37:58 PM

there is no treadmill force. the force of the treadmill is entirely excerted on the wheels. put on some roller blades, stick your feet up and let arab spin one of the wheels and we'll see if you can feel it rolling.


the treadmill is a pussy.

1/29/2008 4:40:23 PM

so, if i put on rollerblades and stand on a treadmill with my arms out, will I take off? No

If i had engines strapped under my arms pushing me, would I?

1/29/2008 4:40:33 PM

^ yes

the question:

a plane is on a treadmill. if the treadmill runs in the opposite direction (the belt spinning) of the plane at the same speed. will the plane take off?

the answer:

yes, the treadmill affects wheel speed and has a minimal effect on the plane. thus the thrust from the plane causes the plane to move forward relative to a observer not on the treadmill and take off.

[Edited on January 29, 2008 at 4:41 PM. Reason : s]

1/29/2008 4:40:48 PM

Quote :

"If i had engines strapped under my arms pushing me, would I?"

do you have wing shaped arms?

1/29/2008 4:41:16 PM

here is the original question

Quote :

"A plane is standing on a runway that can move (like a giant conveyor belt). This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction). Will the plane be able to take off?"

note it says SPEED, not FORCE. The plane moves forward faster and faster (relative to the ground/air around it), the treadmill/conveyor runway moves faster and faster (matching the forward speed of the plane) in the opposite direction = wheels spinning really fucking fast until the plane takes off.

1/29/2008 4:41:33 PM

^ yep. the side question is which would happen first, wheel failure or take off

1/29/2008 4:42:32 PM

^x7?

It doesn't matter. It takes such a small amount of force to overcome the friction of the wheels that even if the treadmill was running 500mph a small airplane could still take off. Maybe at a higher treadmill speed this wouldn't be the case, but that speed would be much higher than the maximum speed of the plane in question.

[Edited on January 29, 2008 at 4:43 PM. Reason : You guys are posting much too quickly.]

1/29/2008 4:42:35 PM

exactly

1/29/2008 4:43:02 PM

^^^ thats a different question all together

[Edited on January 29, 2008 at 4:43 PM. Reason : ^^^]

1/29/2008 4:43:20 PM

Now as for the helicopter on a turntable:
Assuming no tail rotor, it would not take off.

[Edited on January 29, 2008 at 4:52 PM. Reason : Even with a tail rotor, it would not take off.]

1/29/2008 4:45:50 PM

most of the rabble rabble in here doesn't make any fucking sense. probably because most of you are idiots. if the plane is able to overcome the treadmill & move forward relative to a point on the ground, what the fuck was the point of the treadmill in the first place?

if the treadmill matches the plane exactly, keeping the plane from moving relative to the ground, then why the fuck is this so difficult for some of you?

Quote :

"I'm an eingineer!"

Quote :

"I'm a pilot!"

Quote :

"I studied X!"

biggest bunch of retarded smart people. ever

[Edited on January 29, 2008 at 4:57 PM. Reason : *]

1/29/2008 4:56:03 PM

^^ depends if its in the center of the turntable or not

^

Quote :

"f the plane is able to overcome the treadmill & move forward relative to a point on the ground, what the fuck was the point of the treadmill in the first place?"

to mind fuck you...which it obviously did since you said...

Quote :

"if the treadmill matches the plane exactly, keeping the plane from moving relative to the ground, then why the fuck is this so difficult for some of you?"

the treadmill will not keep the plane from moving relative to the ground...thus it will take off

[Edited on January 29, 2008 at 4:59 PM. Reason : ...]

1/29/2008 4:56:31 PM

say you had a sailboat with wheels on a treadmill....

Quote :

"if the treadmill matches the plane exactly, keeping the plane from moving relative to the ground"

cause it's a plane, not a fucking car, and that shit can't happen

[Edited on January 29, 2008 at 4:58 PM. Reason : s]

1/29/2008 4:56:56 PM

Quote :

"2) Assumptions: There is surface friction between the wheels and the belt, meaning whenever the belt moves, the wheels will move with it, never losing contact. However, there is zero friction between the wheel bearings and the axles. Therefore, if a plane was sitting still on the belt, and the belt started moving, the wheels would start to spin. But since there is no friction between the wheels and the axles, the wheels would literally be spinning, but the plane would not move at all. The belt could accelerate as much as it wants, and the wheels would simply spin to keep up, but the plane wouldn't move (if there was no friction between the wheels and the axles) Once again, as soon as the engines are turned on, they would provide thrust and the plane would move forward, eventually taking off just as in scenario 1. During this acceleration of the plane, the belt could go faster or slower or whatever, and it wouldn't matter. All it would do would spin the wheels faster or slower, but since there is no friction between the wheels and the axles (i.e. between the wheels and the rest of the plane) this wouldn't effect the overall acceleration or take-off of the plane."

This statement is false. The plane WOULD move. The lack of friction in the bearings means that the wheels won't exert TORQUE on the axle. Imagine if there were no plane attached to the wheel. The wheel would move down the runway. Attaching a plane to the wheel by frictionless bearing doesn't change the laws of physics. It still takes horizontal force to hold the wheel still.

What would actually happen is the plane would move backwards as the wheels accelerate to match the speed of the treadmill. As the wheels approach the treadmill speed, the plane would decelerate due to friction with the air until the plane was stopped and the wheels were spinning freely beneath it. The plane WOULD move. If at this point you slowed the treadmill, the plane would move FORWARD as angular momentum from the wheels is transferred to the forward momentum of the plane, and the plane would again come to a stop.

With frictionless bearing the plane WOULD move, but not very much and only as long as the wheel speed didn't match the treadmill speed. The plane would only stay completely motionless if the wheels had a ZERO moment of inertia.

I think this is the argument SandSanta is making. However, I don't think he realizes that in order to counteract TENS OF THOUSANDS of pounds of thrust, the treadmill would have to be accelerating at hundreds or thousands of g's (and the wheels would explode from heat and centrifugal forces).

The engines in a plane or jet have enough force to accelerate the entire mass at around 3 g's. In order to maintain zero forward motion, the entirety of that force would have to be transferred into the angular momentum of the wheels. The treadmill could stop accelerating when the viscosity of the air provided sufficient torque in the wheels to counteract the thrust of the engines and the plane wouldn't move. If I had to estimate, I'd say this would arrive when the wheels are spinning at around a few hundred thousand RPM. If you could measure the energy dissipated in the air at the wheels during this state, you would have constructed the world's largest dynamometer and you could determine the power output of the engines.

1/29/2008 4:58:35 PM

Quote :

"a plane is on a treadmill. if the treadmill runs in the opposite direction (the belt spinning) of the plane at the same speed. will the plane take off?"

Ok, the question is so fucking vague, that whole argument is contingent on whether "same speed" means that the plane is at a standstill relative to the air and/or someone standing on the ground NOT on the treadmill, and at this point can it take off?

no


The other stance seems to assume that the plane generates just enough force to overcome the friction between the wheel and the treadmill, and only then do we hit the throttle... can it take off?

yes

1/29/2008 5:00:54 PM

put a bottle rocket on a paper airplane attached to a matchbox car, stick that shit on a gladiator treadmill ramp and you just see what happens

[Edited on January 29, 2008 at 5:01 PM. Reason : p]

1/29/2008 5:01:00 PM

Quote :

"if the treadmill matches the plane exactly, keeping the plane from moving relative to the ground"

in short, becase

Quote :

"cause it's a plane, not a fucking car, and that shit can't happen"

in a little more detail, because the treadmill cannot and does not have any effect on the trust provided by the engines. The engines apply a force against the air, not against the ground/treadmill

1/29/2008 5:01:09 PM

Ok, let me use this example again for those of you out there that still think the plane will not take off.


You have a friend who is wearing roller skates. Think of him as being the plane. He is standing on one of those moving sidewalks(the treadmill) they have at the airport. It is not turned on yet. You are standing to the side on stationairy ground with your hand against your friends back. The moving sidewalk is turned on at this point to a speed of say 5mph. Your friend is remaining stationary because the small amount of force you are putting on his back is holding him in place. Imagine the force of your hand pushing on his back is the thrust of the engines. No matter how fast the treadmill goes, it required the same amount of force to hold him in place. Now say they crank up the treadmill to 180mph, the speed it takes most planes to take off, your hand against his back is still holding him right in place. At this point you begin to walk at a nice steady pace of 6 mph while pushing him along the moving sidewalk. If you don't think it will take off, then explain to me how the moving sidewalk can be going 180mph in one direction, while I am pushing my friend, with total ease, at only 6mph in the other direction. By your logic, I would have to be running at 186mph while pushing him in order to move him forward at 6mph. The plane is free to move forward at any speed regardless of how fast the treadmill is moving in the opposite direction.

Do you understand now that the plane will take off?

[Edited on January 29, 2008 at 5:05 PM. Reason : ,]

1/29/2008 5:01:14 PM

Quote :

" This statement is false. The plane WOULD move. The lack of friction in the bearings means that the wheels won't exert TORQUE on the axle. Imagine if there were no plane attached to the wheel. The wheel would move down the runway. Attaching a plane to the wheel by frictionless bearing doesn't change the laws of physics. It still takes horizontal force to hold the wheel still."

you're right. My scenario #2 was flawed. the end result is the same, though.
And the overall point in scenario 3 is true also

1/29/2008 5:04:12 PM

Quote :

"if the treadmill matches the plane exactly, keeping the plane from moving relative to the ground, then why the fuck is this so difficult for some of you?"

the whole point is, a treadmill can't move the plane (assuming the wheels on the plane move freely -- which they do)

^^great example.

[Edited on January 29, 2008 at 5:07 PM. Reason : .]

1/29/2008 5:05:29 PM

^^^ yeah that is the best example i've seen. it really bothers me that so many people can't grasp the concept of this simple physics problem.

on a side note...it think we convinced all of the doubters that the plane will take off

1/29/2008 5:11:45 PM

Quote :

"it think we convinced all of the doubters that the plane will take off"

sure, given certain assumptions that were not stated in the original question.

1/29/2008 5:13:05 PM

What part of the original question was not clear?

The whole point of the question is that it assumes most people think a plane operates like a car on a treadmill, which it doesn't. So when you pose the question, "Will a plane take off on a treadmill if it is matching the planes speed?" some people automatically say no because they don't understand the difference between a plane on a treadmill and a car and how they react to the forces of the treadmill.

.

[Edited on January 29, 2008 at 5:19 PM. Reason : .]

1/29/2008 5:16:17 PM

Quote :

"sure, given certain assumptions that were not stated in the original question."

the original question made statements that were illogical.

1/29/2008 5:17:03 PM

Hopefully my example has ended this argument.

1/29/2008 5:20:12 PM

^^^

Quote :

"a plane is on a treadmill. if the treadmill runs in the opposite direction (the belt spinning) of the plane at the same speed. will the plane take off?"

1) will it take off now (when the speed of the plane = the speed of the treadmill)?

or

2) will it take off after increasing the thrust such that the necessary speed relative to the air is reached?


Everyone that says the plane will take off is arguing #2, which adds another clause to the question that was not originally stated. Obviously it will take off under this circumstance, but #1 takes the question literally, which is that if the plane speed = treadmill speed, or in other words, the plane's engine exerts just enough force to overcome the friction between the tire and the treadmill, will it now take off? NO

Your example basically illustrates #2

[Edited on January 29, 2008 at 5:22 PM. Reason : adsf]

1/29/2008 5:21:26 PM

It will take off in #1 also. Look at my example again, the plane is free to move at any speed forward. So, if the treadmill is moving one way at 180mph the plane only has to move forward at a few mph to be stationairy. At this point it can accelerate to 180mph, an equal speed of the treadmill. It will not be stationary at this point, instead it will be moving down the treadmill at 180mph while the treadmill is moving in the opposite direction 180mph. The wheels will be spinning at 360mph when the speads are matched.

[Edited on January 29, 2008 at 5:27 PM. Reason : .]

1/29/2008 5:26:34 PM

Quote :

"1) will it take off now (when the speed of the plane = the speed of the treadmill)? "

The way you're interpreting the question is a trick question scenario.

The treadmill can't actually stop the plane from acceleration. So it doesn't matter what the speed of the treadmill is after the engines reach the very marginal amount of thrust to break the force of friction in the wheels (ie an inefficiency in the system) (see the video posted earlier-- once the props are spinning a certain amount, the plane remains still no matter the speed of the treadmill).

At this point, the treadmill could be going a million miles an hour and the plane just has to throttle up as normal to take off, no extreme ridiculous throttling or anything.

To recap, the treadmill can't meaningfully affect the motion of the plane. As sparky noted earlier, the treadmill is introduced to mind-fuck you. It is meant to be a trick question, a riddle if you please, to cause discussions like this one.

The plane will take off, in all normal conditions of being on a treadmill.

Quote :

"Obviously it will take off under this circumstance, but #1 takes the question literally, which is that if the plane speed = treadmill speed, or in other words, the plane's engine exerts just enough force to overcome the friction between the tire and the treadmill, will it now take off? NO"

okay, this is true. But why would a pilot on a treadmill just throttle up the very moderate amount just to overcome friction and stay still? What would be the point of this? Why would someone even have to wonder about this?

[Edited on January 29, 2008 at 5:31 PM. Reason : ]

1/29/2008 5:29:08 PM

Quote :

" At this point it can accelerate to 180mph"

Now you're back in the realm of #2

at any rate, I think once we all use the same assumption, everyone agrees -- the plane has to move fast enough relative to the air (or non-treadmill earth) to take off

1/29/2008 5:30:18 PM

its all about the air

1/29/2008 5:31:54 PM

the original question asks if the plane could take off which insinuates full throttle/thrust

the only difference between the plane taking off on a normal run way vs. on a runway that can move like a treadmill is the speed at which the wheels will be spinning

[Edited on January 29, 2008 at 5:32 PM. Reason : ..]

1/29/2008 5:32:06 PM

How am I back at #2?

The plane is going 180mph forward, while the treadmill is going 180mph in the opposite direction. That is #1 that you posted correct?

The treadmills speed = the planes speed


I think you are missing the point that the plane only has to apply minimal thrust, say to speed the plane up to 10mph to counteract the 180mph in speed the treadmill is going in the other direction.

[Edited on January 29, 2008 at 5:34 PM. Reason : .]

1/29/2008 5:32:20 PM

Quote :

"I think you are missing the point that the plane only has to apply minimal thrust, say to speed the plane up to 10mph to counteract the 180mph in speed the "

No, this is my point exactly, as far as scenario 1 is concerned. At this point, it can't take off.

Only after sufficiently increasing the throttle, will it take off.

but yes, obviously there was a complete disjoint in how i and a few others interpreted the question versus others.

1/29/2008 5:37:39 PM

Quote :

"the only difference between the plane taking off on a normal run way vs. on a runway that can move like a treadmill is the speed at which the wheels will be spinning"

Exactly, going back to my moving sidewalk example, I can push my friend along at 6mph with the moving sidewalk turned off. At this point, the wheels are spinning 6mph. Now if the sidewalk is turned on to a speed of 20mph, I can still push him along with ease at 6mph. The only difference now is that the wheels on his roller skates are moving 26mph now.

Quote :

"Only after sufficiently increasing the throttle, will it take off. but yes, obviously there was a complete disjoint in how i and a few others interpreted the question versus others. "

Yeah, I don't really see how you guys saw it that way. Obviously the throttle has to be sufficiently increased in order for it to take off, thats true even on a normal runway.


There was no mention in the original question as I recall, of not increasing the throttle. So I am not really sure where you came up with that.

Quote :

" No, this is my point exactly, as far as scenario 1 is concerned. At this point, it can't take off. "

No, obviously, the plane is only traveling at 10mph. Which does not equal the speed of the treadmill which is going 180mph, which is not what you said in #1. You said treadmill speed = plane speed. Using your scenario in #1 you are saying 10mph = 180mph



[Edited on January 29, 2008 at 5:43 PM. Reason : .]

1/29/2008 5:37:46 PM

Quote :

" No, this is my point exactly, as far as scenario 1 is concerned. At this point, it can't take off. Only after sufficiently increasing the throttle, will it take off. but yes, obviously there was a complete disjoint in how i and a few others interpreted the question versus others."

Well, in the scenario you imagined, even if the plane were not on a treadmill it wouldn't have taken off. Which would make it pointless to ask such a question anyway.

1/29/2008 5:44:12 PM

So, does everyone now understand that the plane will take off?

1/29/2008 5:48:47 PM

^

well, the whole question is pointless, since all other things being equal, the treadmill has no significance.

[Edited on January 29, 2008 at 5:50 PM. Reason : adsf]

1/29/2008 5:50:32 PM