Lähteekö lentokone lentoon liukuhihnalta?

Ap:N pointti oli se että lentokone ei liiku, joten se ei silloin nouse ylöskään, se kun ei ole helikopteri.

Vierailija:

Ap:N pointti oli se että lentokone ei liiku, joten se ei silloin nouse ylöskään, se kun ei ole helikopteri.

Siinä on se ero.

voidaan tulkita kahdella tavalla.



Jutun oikea kätsi on se, että sillä saadaan ensinnäkin ikuisuuskiista aikaan ja toisekseen sen kiistan aikana moni oppii paljon fysiikasta. Ei ihan huono kysymys siis.

Perustelkaa!

näillä on ei lähde lentoon-hemmoilla on hyvin jäsenneltyä ja heidän ajattelutavallaan järkeviä perusteluja. Voisi olettaa että takana on ainakin amk, ehkä jopa yliopistotason koulutusta, ei tosin vaativilta tieteiltä, heidän älykkyytensä ei yksinkertaisesti riitä.



Mikäli näin päivänselvässä asiassa on jo epäselvyyksiä niin miten olisi kun eteen tulisi jokin oikeasti vaativa tehtävä?



Romahdus?

(olemalla noin tiukasti oikeassa, oikeassa sä tietenkin olet, sulta menee ohariksi puolet tämän kysmyksen opetuksesta. Mutta ei se mitään. Jatka vaan suorittavissa hommissasi)

Ajatettele vaikka sit niin että renkaat EI kestä, joten EI nouse.

tehtävää pitää ajatella pelkän teorian kannalta jo senkin takia, että moisen liukuhihnan rakentamisessa saattaisi tulla " pieniä" ongelmia

Täälläkin moni lentäjä yms sanonut että ei nouse. Paremmin ne kuitenkin asian tietää.

Täälläkin moni lentäjä yms sanonut että ei nouse.

taitaa vaan harmittaa kun huomasit olleesi puoli ketjua väärässä

Jos joku oikeasti haluaa vakuuttua asiasta niin googlettaa: airplane conveyor tai käy lukemassa faktaa vaikka tiede-lehden palstalta.

Vierailija:

Jos kysymyksessä olisi sidottu hihnan nopeus renkaiden pyörimisnopeuteen, auto ei liikkuisi paikaltaan. Mutta kysymyksessä ei puhuttu mitään renkaiden nopeudesta vaan liikkumisesta. [b]Tällöin tietty myös lentokone pysyisi paikallaan...[/b]

Eihän tuo tarvi kuin vähän fysiikan tuntemusta että sen tajuaa.

Dear Cecil:



Please, please, please settle this question. The discussion has been going on for ages, and any time someone mentions the words " airplane" or " conveyor belt" everyone starts right back up. Here' s the original problem essentially as it was posed to us: " A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?"



There are some difficulties with the wording of the problem, specifically regarding how we define speed, but the spirit of the situation is clear. The solution is also clear to me (and many others), but a staunch group of unbelievers won' t accept it. My conclusion is that the plane does take off. Planes, whether jet or propeller, work by pulling themselves through the air. The rotation of their tires results from this forward movement, and has no bearing on the behavior of a plane during takeoff. I claim the only difference between a regular plane and one on a conveyor belt is that the conveyor belt plane' s wheels will spin twice as fast during takeoff. Please, Cecil, show us that it' s not only theoretically possible (with frictionless wheels) but it' s actually possible too. --Berj A. Doudian, via e-mail



Cecil replies:



Excuse me--did I hear somebody say Monty Hall?



On first encounter this question, which has been showing up all over the Net, seems inane because the answer seems so obvious. However, as with the infamous Monty-Hall-three-doors-and-one-prize-problem (see The Straight Dope: " On Let' s Make a Deal" you pick Door #1, 02-Nov-1990), the obvious answer is wrong, and you, Berj, are right--the plane takes off normally, with no need to specify frictionless wheels or any other such foolishness. You' re also right that the question is often worded badly, leading to confusion, arguments, etc. In short, we' ve got a topic screaming for the Straight Dope.



[b]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.[/b]



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.



--CECIL ADAMS

sori

googletappa vielä niin tajuat sen lentoonlähdön kyllä....

tai ääliömäisyydessäsi.



et osaa englantia etkä googlettaa niin mitä muutakaan voi odottaa.



KONE NOUSEE ILMAAN!

Lue uudestaan ketju ja mieti nyt itsekin hyvä ihminen!

www. google. fi/search?hl=fi&q=lentokone+liukuhihnalla