When a plane is sitting on a tarmac, it takes a tremendous thrust just to get the plane rolling. Actually, even at idle thrust, you're well advised to keep your feet on the brakes at the Hold Short line in most jets I've flown. Even if you consider the dynamic drag of the rolling tires, the horizontal force vector is at least an order of magnitude less than the thrust of the engines, probably a couple orders of magnitude at full thrust. Think of the "land speed record" type of jet cars...300+knots ON THE GROUND...ground speed as high as in our experiment except that there's also 300+knots worth of aero drag as well, instead of just 150 knots! If the jet car grew wings, it'd fly.

In any case, as I mentioned several pages ago, this is a thought experiment and the convention is that you don't get to add your own set of variables to thought experiments. Calculating the rolling resistance just wasn't set in the conditions of the riddle.

Easy. It's basic math.

Throw ten rocks on the ground. Then pick up the ten rocks. How many rocks are left on the ground?

Answer: 0

The airplane example is just to get you to think about jet engines, rolling resistance and lift on the wings and blah...blah..blah.. to confuse you. It does not matter if the object going down the belt at 10 mph is a jet with large tires, a car, a skateboard with small tires, a beachball, explosive diarrhea, space shuttle, or Carl Lewis sprinting down it.

10 mph is 10 mph. I could put a "Slip & Slide" on a belt. If I slide down it at 10 mph, and someone turns it on to 10 mph, I'm going to become stationary.

This like the 10 pounds of feathers vs. 10 pounds of steel question.

Am I a member of MENSA now??

It does not matter if the object going down the belt at 10 mph is a jet with large tires, a car, a skateboard with small tires, a beachball, explosive diarrhea, space shuttle, or Carl Lewis sprinting down it.

Actually, it matters a great deal, as the dynamics of these examples are not all the same. This has been amply explained by some of the previous posters, who must be groaning in frustration when they see how their efforts have failed to penetrate the reasoning barrier. What role in evolution do you suppose this barrier has played for Humans? Perhaps it provides a necessary brake on runaway technological development, without which, we would have exterminated ourselves long ago.

I can imagine a comparable dilemna 50,000 years ago, when the inventor of the spear-launcher tried unsuccessfully to convince the other members of the hunting party why it was better to have a doubled throwing range.

This dog won't fly.

You can leave the wheels out of the discussion. Assume the plane has frictionless wheels with no mass. The engines provide thrust as Richard has correctly described. The wings require air flowing over them to provide lift. The engines do not provide this airflow, it is provided by the movement of the aircraft relative to the air. If the aircraft has a rotation speed of 100 knots and there is a tailwind of 10 knots the airplane will rotate at a speed relative to the ground of 110 knots and the pilot will see 100 knots on his airspeed indicator (ASI). If there is a headwind of 10 knots the aircraft will rotate at 90 knots ground speed and the pilot will see 100 knots on his ASI. If there is no wind and a seaplane is on a river flowing at 10 knots and the pilot takes off in the direction opposite the flow of the river he will depart the Earth when his speed relative to the ground is 100 knots and his speed relative to the river is 110 knots. His ASI will register 100 knots.

If the airplane's forward movement is offset by movement in the opposite direction as in the conveyer belt thought experiment then there is no airflow over the wings and therefore no lift. The ASI will register 0 knots and the airplane will not fly.

For the last time.

The airplanes forward movement is NOT offset by the converyor belt.

There is NOTHING offsetting, or counteracting the thrust of the engines.




AB SO LUTELY NOTHING is offsetting the thrust.

The converyor belt interacts with the wheels, and the wheels ROTATE twice as fast, to offset the conveyor belts backward movement. It's as simple as that.

Simple Math.

As I stated in POST #11 and other posts thereafter. In order for the thrust of the engines to be 'negated' an equal and opposite thrust must be provided. AGAINST THE AIRFRAME. For this is where the thrust is being applied. There is no force being applied against the ground by the wheels in order to get the plane moving, such as there is in a car to get a car moving.

The movement of the conveyor belt applies friction againts the wheels, and the wheels ROTATE in response to this friction.

That is the function of the wheels. It takes comparitively little force to get the aircraft moving, in fact. Anyone recall the truck commercial (Dodge I think) that had a truck towing a 747? They made a big deal about it untill volkswagon towed one. The wheels and bearings are designed to minimize the friction.

If your plane was attached to a rope anchored a the front end of the runway, and the converor belt was started up, with the engines OFF - the wheels would ROTATE under the plane, without the plane moving. THE wheel rotation is INDEPENDENT of the planes 'ground speed' because of the static force of the rope, which acts on the airplanes body independant of the rotation of the wheels and speed of the converyor belt.

Same for a person in rollerskates standing on a treadmill and holding onto the side bars. The wheels rotate at whatever speed the treadmill passes under them. The motion of the person standing is independent of the treadmill, because of the static force between his hands and the rails. He can even PULL himself forward on the treadmill, and the wheels on the rollerskates will rotate FASTER than the treadmill, because of the added forward momentum. Because his arms on the sidebars are INDEPENDANT FORCES acting on his body, not interconnected or related to the treadmill. Just. Like. The. Engines.


The Planes thrust is generated independent of the motion of the wheels. The planes forward motion is NOT generated or determined by the velocity of the wheels rotation. The planes wheels are simply acting as 'bearing's to 'lubricate' the friction between the ground and the plane. The wheels are not turning when the plane lands, and that doesn't stop the plane. They simply accelerate up to speed as the plane lands. That is their function. As the plane applies thrust it will move forward. The converyor belt will move backwards, and the wheels will rotate at twice the speed they normally would in response.

The. Plane. Will. Fly.

One final illustration for those who have difficulty understanding that the plane will fly because its motive force is independent of its relationship of its wheels to the ground.

Assume a HUMMER is parked on our imaginary runway. The runway is rigged to respond to the Hummer’s forward motion, by moving BACKWARDS at the same speed. You get in, and start the engine, and accelerate. As the wheels TURN to move the vehicle forward, the conveyor belt moves BACKWARDS at exactly the same speed. The net forward movement of the Hummer is ZERO. (At least to an independent observer standing off to the side. The speedometer will read acceleration to the driver.)

It is exactly like walking on a treadmill and having the tread mill match your speed. It is just like walking on an escalator, at the same speed, and standing still. Indeed, who among us has not done this? It is such a simple concept, that we are inclined to apply the same physics to our aircraft.

That would be a mistake.

For unlike the Hummer, or a Human on a treadmill or escalator, forward motion is NOT generated by exerting force against the ground, (And having the ground ‘push back’)

THAT IS THE FALACY in assuming it will stand still.

Now, back to the Hummer. It is still sitting on our runway, but this time we have modified it. We have disengaged the wheels from the engine completely. They are free to rotate. We HAVE modified the engine however, as we have connected it to a winch, mounted on the front of the vehicle. The winch is attached to a steel cable, a mile long. The other end of the cable is attached to a post, OUT BEYOND the end of the runway. It is not “connected” in any way to the surface of the runway.

The conveyor belt runway is still ‘rigged’ to move backwards at the same speed that the Hummer moves ‘forward’.

We start the engine, and engage the winch, which starts ‘winding’ the cable onto its drum, PULLING THE HUMMER FORWARD. (We also know that the engine, towline and winch are strong enough to tow the Hummer forward, because we have used them before, just as we know the engines of the aircraft are more than strong enough to generate speed for takeoff)


What does the conveyor belt do? Why, it’s rigged to move in the opposite direction… so it does that.

What do the WHEELS on the hummer do? Why they rotate, because they are free to do so, having been disengage from the drive train in any manner.

What does the HUMMER do? It moves forward, being ‘towed’ along by the cable attached to the drum. IF we ‘accelerate’ the winch, the Hummer’s forward motion will also accelerate.

In response, the conveyor also accelerates.

The wheels turn TWICE AS FAST as they normally would to an observer standing by the side of the conveyor belt runway.

The hummer MOVES FORWARD because the method of impulsion is not coupled to the interface between ground and tires. Even though the ENGINE for it’s movement is still attached to the Hummer’s body, it is applying a force that is NOT generated AGAINST THE GROUND (as it’s wheels were before.) It is independent of this.

Same thing would happen to our person in roller skates on a treadmill, holding a rope, and ‘pulling himself along’ by his arms. The roller skates would simply rotate at a speed that would appear to be ‘greater’ than the normal forward velocity, but there is nothing impeding his forward motion.

In the examples of the Hummer and the Human, the impulsion forces acting on the ‘bodies’ (fuselage, airframe) of both, are independent of the interface of the Hummer and Human with the treadmills. The impulsion force is independent of the speed of the Hummer’s wheels, or those of the Human’s roller skates.

When discussing the four factors affecting the airplane, LIFT, THUST, GRAVITY and DRAG, the only element that is being altered is DRAG. The drag of the runway AGAINST THE WHEELS. But the wheels are designed to rotate at ANY SPEED NECESSARY to facilitate a smooth interaction between the aircraft and the ground., and so eliminate, or minimize such a force. So they will simply rotate twice as fast as normal, and the plane will lift off.

The. Plane. Will. Fly.

Richard, the problem as posed introduces a feedback mechanism that causes the conveyer belt speed to match "the speed" of the airplane. I put the speed in quotes because the problem doesn't state how that speed is measured. If that speed is the forward speed of the aircraft, then my interpretation is correct. Aircraft speed is measure using an airspeed indicator and uses air pressure, not rotational speed of a wheel. If it is the wheel rotation, then you are closer to being correct, and good enough for a thought experiment.

I am a pilot, I know how airspeed is measured in flight, and the difference between airspeed and groundspeed.

The thought experiment postulates that as the aircraft moves forward, the conveyor belt moves 'backwards' matching its speed.

The 'apparent' speed of the aircraft to an observer standing off to the side of the runway/belt is a continual accelleration forward.

The 'apparent' speed of the aircraft in IAS (indicated airspeed) in the cockpit will be EXACTLY the same as if the aircraft were taking off from a stationary runwary. (Assuming still air.)

The 'apparent' ground speed, if reading off of a speedometer attached to the wheels, would indicate TWICE the apparent ground speed to an observer standing off to the side of conveyour belt.

The plane will fly, even if the conveyor belt is moving at twice or three times the speed of the aircraft.

The conveyor belts motion has very little effect on the aircraft's forard motion, it's main effect is the rotational speed of the wheels.

The Planes FORWARD motion is NOT offset by the conveyor belt/runway. The Planes ROTATIONAL WHEEL SPEED is. That is the only affect the belt has on the plane.

The. Plane. Will. Fly.

I am a pilot, I know how airspeed is measured in flight, and the difference between airspeed and groundspeed.

Oh good. Me too. We'll have to go flying sometime.


The thought experiment postulates that as the aircraft moves forward, the conveyor belt moves 'backwards' matching its speed.

Good so far, but to make absolutely certain we agree on this point it is my understanding of the statement of the problem that the conveyer belt moves the AIRCRAFT backwards at a rate that instantaneously compensates for any detected forward movement of the aircraft as measured by the airspeed indicator. This implies that the ASI will always register 0.

The 'apparent' speed of the aircraft to an observer standing off to the side of the runway/belt is a continual accelleration forward.


This is incorrect, but irrelevant. The only thing that matters in this problem is the airspeed registered on the ASI, which you have established as 0.

I rescind my previous statement...at some point the bearings of the wheel would fail, connecting the airframe to the treadmill...then the treadmill would be pushing directly against the airframe and would also fail...with all the available pieces disconnecting the airframe from the ground, the airplane would melt into oblivion and not fly!

Okay, we're going to leave out bearings failing or tires blowing out, for the same reason we're going to leave out the pilot spilling coffee on his lap and hitting reverse thrust, or a flock of geese getting sucked into the engines.

Now, lets go back to the original stipulations of the thought experiement.

"If you have a large jet plane (747) sitting on a runway that was actually a giant conveyor belt (go with it). And there is also a device on the plane that communicates with the conveyor belt to tell it how fast the plane is traveling, which would then make the conveyor belt match the speed IN REVERSE."

The 'device' communicates with the conveyor belt to tell it how fast the plane is travelling.

Since the airspeed indicator is our 'speedometer' then it would be sending it's apparent airspeed to the conveyor belt.

The engines apply thrust.
The plane moves.
The airspeed indicator advances.
The belt moves backwards.
The wheels ROTATE at twice the speed they normally would.

The plane flies. The airspeed indicator would always read what it normally would at takeoff. (Assuming still air, as no head/tail/or crosswinds were stipulated.)

There is a curious effect, IF the 'device' measuring the planes 'speed' were NOT an airspeed indicator, but rather a speedometer attached to the wheels... such as in an automobile. (I've never flown a 747, only small single engine craft and sailplanes... NO engines! More fun..) then there would be a difference between the speed of the belt and the plane.

At any rate. IF the 'device' sensing the airplanes 'speed' WERE a speedometer sending it's speed to the runway, THEN the speed of the runway would NOT match the forward speed of the aircraft. It would ACCELLERATE at EXPONENTIAL rates. (The sensor in the wheel says it's moving at ten knots, the runway accellerates, the wheel rotates twice as fast, more accelleration, ETC... ALL INDEPENDENT OF THE AIRSPEED of the Jet through the air. As, indeed groundspeed is always independent of IAS or TAS)

At some point, would the bearings fail and the tires blow before the plane rotates? I don't know. But again, I don't know if the geese fly into the engine, the pilot spills his coffee, or the device that powers the runway/belt runs out of fuel... all irrelevant to the thought experiment.

The point is, the movement of the ground beneath the plane has no bearing on the planes forward movement through the air, even if the plane is trailing it's wheels on the ground. (Yes, yes, increased friction in the bearings, wear/tear on the tires aside please... the plane still moves forward.)


(Jim, please note that the thought experiment does not say the belt moves the airplane backwards. It says that the speed of the belt is set by the airplane, and that the belt moves 'in reverse'. I never said the airspeed would indicate 0)

If the conveyer belt does not move the airplane backwards at a rate that equally and instantaneously compensates for its forward motion then I agree with your analysis.

That's one heck of a very long conveyer belt by the way. Assuming it ain't a STOL aircraft...

The conveyor belt only moves 'in reverse' in response to the planes forward motion... being driven by the thrust of the engines. It cannot/does not/ move the plane backwards, or cause it to remain stationary.

And with that,

The earth IS round.

It revolves AROUND the sun.

Elvis is STILL dead.

The. Plane. Will. Fly.


I'm outahere....

Well, actually the earth is very close to, although not perfectly, spherical and it orbits around a mutual center of mass with the sun (and other masses wandering around the neighborhood).
:-)

But I do also really believe that Elvis is still dead...and earnestly hope this riddle and thread will be equally deceased!

I shoulda changed the topic of this thread to "OT: Any pilots here? ;) "

If Elvis is in the plane versus standing on the conver belt, the plane won't fly. It would ruin the thrust/weight ratio versus if he were standing on the belt which would slow the belt down, but have no effect on the friction in the planes wheel bearings thus reducing drag and rotational mass of the wheels because this time of year the earth is farthest from the sun keeping gravitational pull to a minimum allowing the planes wheels to spin at maximum thermal and frictional efficiency and allowing tire expansion to a maximum at higher speeds. Also note that cooler air tempatures produce more dense air and will produce more engine power, allowing the jets engines to overcome the weight of Elvis standing on the conveyer belt.

This Plane Won't Fly.

Adam, Adam , Adam,

If Elvis is on the plane...

It's ALREADY flying....

No way man, even with Elvis on the plane, the plane will fly.

The reason is down in the avionics bay underneath the cockpit is a Rockwell Automation Retro-Encabulator that not only provides inverse reactive current for use in unilateral phase detractors but is also capable of automatically synchronizing cardinal grammeters. Check it out for yourself:

http://video.google.com/videoplay?docid=-2081189882805593268

Case closed. This baby is going to fly.

No way man, even with Elvis on the plane, the plane will fly.

The reason is down in the avionics bay underneath the cockpit is a Rockwell Automation Retro-Encabulator that not only provides inverse reactive current for use in unilateral phase detractors but is also capable of automatically synchronizing cardinal grammeters. Check it out for yourself:

http://video.google.com/videoplay?docid=-2081189882805593268

Case closed. This baby is going to fly.

Tim:

Actually, what the Rockwell people are saying is it won't fly without the Automation Retro-Encabulator. But that equipment wasn't included in the original scenario. So it won't fly....

So, which came first: the chicken or the egg? Why?

The conveyor belt only moves 'in reverse' in response to the planes forward motion... being driven by the thrust of the engines. It cannot/does not/ move the plane backwards, or cause it to remain stationary.

And with that,

The earth IS round.

It revolves AROUND the sun.

Elvis is STILL dead.

The. Plane. Will. Fly.


I'm outahere....

I thought that the Earth ORBITS around the sun and revolves around it's AXIS. No?
:p

The reason is down in the avionics bay underneath the cockpit is a Rockwell Automation Retro-Encabulator that not only provides inverse reactive current for use in unilateral phase detractors but is also capable of automatically synchronizing cardinal grammeters.

Hehe. All the guys here at work found that hilarious.
Yes, it's an engineering department...

So in answer to the title of this thread....

apparently not! ;-)

Hmmm....if you read the whole thread, I think the answer is still out there waiting to be found!

(I think it will fly because the wheels decouple the airframe (where the thrust is) from the conveyor belt.)

So in answer to the title of this thread....

apparently not! ;-)

That's great Michael, you may have the ultimate post on this thread!!!!!!!!!!!!!!

One Michael to another!

Mike

The Classical Question of “Chicken and Egg”, this question is always asked and asked, therefore I have devised a simple FAQ

Question:

“What came first the Chicken or the Egg?”

Answer:

This question was first asked to demonstrate the circular argument for biogenesis, its a circular reference and thus can not have an answer, it ends in an infinite regress. The only solution is an external agent that is not dependent within the co-dependent loop, i.e. a Creator.

Formal mathematical answer:

(1) Co-existence of two co-dependent entities A and B
(2) A can not exist without the prior existence of B
(3) B can not exist without the prior existence of A
(4) From (2) and (3) a closed loop occurs.

Therefore either can not come first (due to the closed loop), the ONLY solution is to have an independent agent OUTSIDE of the closed loop to bring about the first entity within the loop.


I hope that helps

Anhar Hussain Miah

P.S The plane does fly, I was going to derive from first principle, INCLUDING the control system mathematics involved in the "treadmill", because the feedback system will indeed have a slight delay, but in the end I realised that unlike a Car that requires the friction between the wheel and the road to move forward, the the plane uses propulsion from the engines thrust to move forward (thats the key difference) and perhaps the reason as to why people are having problems in visualizing the riddle.

Some good points stated here and some that seem a bit slanted by a version of Creation Theory.

About chickens: In fact, an egg is a part of every chicken, as much as a placenta and umbilical cord are or have been a part of each one of us. It's included in our genetic codes to have them, even though at hatching or birth, they are discarded and only a small reminder is evident in our case, that they were ever present (Mariette Hartley having two and Kyle XD having none, being rare exceptions). Therefore, neither the chicken or the egg came first, as being integral parts of a single entity, they evolved together from the earliest ancestor that was a clump of self-replicating proteins in the sea. This amorphous forebear preceded eggs, legs, wings or early morning crowing, but nevertheless, is the root of the chicken's family tree.

Some good points stated here and some that seem a bit slanted by a version of Creation Theory.

About chickens: In fact, an egg is a part of every chicken, as much as a placenta and umbilical cord are or have been a part of each one of us. It's included in our genetic codes to have them, even though at hatching or birth, they are discarded and only a small reminder is evident in our case, that they were ever present (Mariette Hartley having two and Kyle XD having none, being rare exceptions). Therefore, neither the chicken or the egg came first, as being integral parts of a single entity, they evolved together from the earliest ancestor that was a clump of self-replicating proteins in the sea. This amorphous forebear preceded eggs, legs, wings or early morning crowing, but nevertheless, is the root of the chicken's family tree.


Mr J. Stephen McDonald, with the greatest of respect I have to stress and disagree that, Unfortunately your entire reasoning depends on assuming from the very foundation that the Modern Synthesis of evolution is actually correct, however a very large part of humanity does not subscribe to that philosophical worldview, further more I see no scientific reason to accept such a false model.

Of course I can see this thread descending into Evolution Vs ID debate, which I will gracefully wish to opt out for the sake of the thread.

However if you wish to know why I have come to such a conclusion, then if you email me I will be more than happy to email the entire transcript of my formal debate on the very topic (Which I won) :)

Anhar Hussain Miah

Of course I can see this thread descending into Evolution Vs ID debate, which I will gracefully wish to opt out for the sake of the thread.Thank you in advance, as we will not use this forum to debate evolution vs. intelligent design. They are, after, completely synonymous terms which both describe the exact same process (in other words, evolution is the mechanism of creation). Thus a "debate" is not only inappropriate, but also impossible, at least in the context of this forum. There, I've managed to iterate that we will not pursue poltical or religious topics here, while getting my own viewpoint aired. Now I can enjoy the morning. Yes, the plane will fly.

If there is no air moving over the wings (no airspeed), there is no lift and there may as well not be any wings at all. It is difficult to take off without wings. However, it is possible to take off without wheels.

As for the lasers, I believe c+k = c, so the light will arrive at the same time regardless of the plane's sublight speed. I could be wrong, though, as I am not well versed in physics.

If there is no air moving over the wings (no airspeed), there is no lift and there may as well not be any wings at all. It is difficult to take off without wings. However, it is possible to take off without wheels.

As for the lasers, I believe c+k = c, so the light will arrive at the same time regardless of the plane's sublight speed. I could be wrong, though, as I am not well versed in physics.

1. Who says there's no air moving over the wings?

2. This assumption is based on the theory that there's the equivalent of a universe-wide grid, within which light moves at a uniform speed that relates only to the grid and not to any motion of an object within the grid, from which the light emanates. The obvious fallacy in this theory is, that if it were true, there would be no Doppler Effect, which causes light coming from celestial bodies to shift in its position in the color spectrum, in relation to its relative speed, towards or away from an observer.

Arrrghh! This thread has reappeared!
Dang it. I KNEW we shoulda locked this thread last time it went quiet!
;-)

The laser question doesn't give enough information. Is the target in the air or on the ground? Is it an orbiting deathstar satellite? What altitude? How high up is the tower where the laser is?

Depending on this info, the distance from the target to the planes laser might be less than the distance from the tower to the target. If the distance is less, the closest laser beam will strike first.

I just found this thread for the first time, read through every reply and I have to go ahead and say ... that I really have no idea what the plane will do.

I'm kind of lost why this hasn't come to a consensus. We were just talking about a problem similar to this in my PHYS261 class. It was a slightly different setup but same properties. The plane will never move off the conveyor belt and thus never generate enough lift via wind velocity (see Bernoulli's principle) to get off the ground. Regardless of the propulsion provided by the engines, the plane cannot leave the conveyor belt if it matches its velocity.

The comparison made previously with ice is not similar in any way. Ice is simply a frictionless surface; this conveyor belt actively negates any horizontal force exerted on the craft to move it.

Yay, Ben... That was my argument back in the early posts. Took a lot of heat from most....

I can't believe I'm going to reply again but what heck, it's a slow Friday night. Ben, the plane will take off. Here's the Straight Dope:

http://www.straightdope.com/columns/060203.html

I'm kind of lost why this hasn't come to a consensus. We were just talking about a problem similar to this in my PHYS261 class. It was a slightly different setup but same properties. The plane will never move off the conveyor belt and thus never generate enough lift via wind velocity (see Bernoulli's principle) to get off the ground. Regardless of the propulsion provided by the engines, the plane cannot leave the conveyor belt if it matches its velocity.

The comparison made previously with ice is not similar in any way. Ice is simply a frictionless surface; this conveyor belt actively negates any horizontal force exerted on the craft to move it.

THE PLANE HAS WHEELS!!!!!!!!!!!

...We were just talking about a problem similar to this in my PHYS261 class...Ben, please send me your physics instructor's email so I can advise him/her to fail you!
;-)

I'm going to resist the almost overwhelming urge to lock this thread. Instead, I think I'll just mercilessly taunt anyone who re-posts any arguments or facts, correct or faulty, that have already been stated earlier in this ridiculously long thread. And then I shall taunt you a second time.

Ben, the mistake you are making is the assumption that the plane will be stationary because the belt matches its speed. I made this mistake too, as you will see if you read the thread. In a realistic scenario there is not enough friction between the plane and belt for this to happen, therefore the plane will eventually move ahead and fly regardless of what speed the belt is running at.

Pete

For the LOVE OF GOD.... FOR WHATEVEVER you hold dear...

PLEASE PLEASE PLEASE LOCK THIS THREAD!!!!

You're killing me man!!!!!!!!!!!!!!!!
(Post #11... THE CORRECT ANSWER)

Don't forget that excellent post #21.

It may be somewhat frustrating, I agree, but no real reason to close it. If it were just about how irritating a post can be, there would be dozens of them closed, starting with most of the ones that ask, "What Tape Do You Use In Your---------," and Should I Use A Cleaning Tape, and What Kind?"

Mike :)

Hey Ben. We jeanusus has to stik two gather !!

Here is a question that will for sure get you guys thinking.

If you have a large jet plane (747) sitting on a runway that was actually a giant conveyor belt (go with it). And there is also a device on the plane that communicates with the conveyor belt to tell it how fast the plane is traveling, which would then make the conveyor belt match the speed IN REVERSE.

Can the jet take off?

Hmmm...

interesting. "speed" in the proposed situation needs to be clarified...ground speed or air speed?

In this problem, if it was ground speed that the conveyor belt would match, there is an issue with theoretical reponse time...

If the conveyor responded instantly (since we're theoretical, we can do that), and it was groundspeed, from the wheels, the jet engines would move the airplane itself forward regardless of the conveyor belt's acceleration as the airplane moves itself through the air...the wheels would be turning infinitley fast as they would continue to accelerate as the belt would accelerate to compensate for the fact the wheels are attached to the plane, which would move forward based on the engines pushing the body, without direct relationship to the wheels rotation speed and inverse motion of the conveyor ...negating kinetic friction of the rubber and the conveyor surface and any operating range of bearings and bushings and flash point of any flammable lubricants contained therein...which would most likely simply incinerate the wheels during the whole procedure...provided the conveyor didn't simply fly apart.

If the conveyor responded to airspeed...largely the same scenario would apply, with the exception of the acceleration curve probably wouldn't be as steep as the groundspeed scenario because the response of the conveyor would be directly inverse to the forward motion of the aircraft (without the acceleration influence of the conveyor's compensatory movement on the wheel acceleration, which creates wheel speed as a rapidly increasing multiple of actual forward motion due to the wheels direct contact with the conveyor), though the acceleration would still be a bit of a logarithmic curve as the belt will have to accelerate, but would max out at the exact inverse of lift off speed.

In the airspeed compensation scenario, the wheels would rotate at a theoretical maximum of 2X liftoff speed (1X for the aircraft forward motion, another 1X to compensate for the inverse belt movement), whereas the groundspeed scenario could create an almost infinite amount of wheel acceleration.

If the wheels didn't burn up and the conveyor belt held together, in either case the airplane would move based on the engines pushing the fuselage, not the relative speed of the wheels, therefore it WOULD move and would takeoff.

:-) Whew!

Ah...yes in the scenario we discussed in class, the conveyor belt (or in our class' example a wheel) was motorized to match the velocity of the airplane.

Actually, our problem dealt with a model plane and a weight, and did involve friction, although it was not stressed as the reason for taking off...I'll take a peek at it again. Perhaps not so parallel a problem after all. Although it still seems to me that if the conveyor belt is actively...no wait, I guess it's frictionless. Sigh.

*steps back* you should probably lock this now.

My Mom is a Mensa member, I am not. I have not read any other responses so here's my input (or lack thereof)...
If I understand it correctly, the plane isn't moving forward, it's staying stationary while this giant belt rolls under the wheels....
No, the plane would have no lift so it could not take off... unless it had thrust similar to a Harrier jet's vertical takeoff, lol...
As long as the pilot doesn't "hit the brakes." (edit)

Ok Dave, I warned earlier that I'd taunt anyone who re-posted info that was already in the thread! Taunt: Of course you're not in Mensa; how could you pass the test if you don't READ!

I may taunt you a second time later, but there's hockey game on the Idiot Box (InHD) at present.

The plane flys.
Weight any 3 cubes against any 3 cubes,then any 2 from the heavy set.
1hour 30minutes.