JPreston

I know - no doubt you've seen my identical thread on hexus.net where there is no end of intellectual credentials being thrown around I also like the people trying to solve this by committee and suggesting I add a poll :confused:

Because that way you get people hung up on treadmills and wheels. The wheels don't drive the treadmill - the treadmill drives the wheels. Planes have wheels for the same reason that wheelbarrows do - but does a wheelbarrow move forward because it has grippy tyres or because someone is pushing it...?

The Joy of Tech comic... laughter is the best tech support. HTH

No - you are just incorrect in taking the 'speed of the wheels' to mean 'the rotational speed of a point that I will arbitrarily set to be on the surface of the wheel'. That is NOT the common interpretation either - when you drive your car at 60mph, how fast are your wheels moving? Do you say 'at 60mph', or 'at a variable speed found by solving some kind of trigonometric function that varies between 0 and 120mph each revolution depending on where my arbitrary point is at the exact instant you asked'? (what speed are your tyres rated for?) If you do insist on defining speed that way, you cannot construct a treadmill that is logically possible even in the world of frictionless wheels and inextensible belts. Not rigorously possible, but you can work it through anyway: The plane and treadmill start off stationary. As soon the plane starts to move forward (which does happen as soon as the engines start) then the (illogical) treadmill (according to the constraints you have introduced) must EITHER run in the same direction the plane is moving and the wheels do not rotate at all, OR the treadmill runs at infinite speed backwards and the wheels spin at (2x ) infinite speed forwards. In both these illogical cases the plane still takes off. And they are only illogical because you have mis-read the question :P The natural interpretation of 'speed of the wheels',which is the only logically consistent one, results in the plane taking off without needing to resort to infinite speeds - the wheels spin only twice as fast as normal.

It all makes sense to me too. Beat me to it with the example of bolting a big jet engine to your roof the next time your car is on a rolling road - fire it up, and as you say bye bye to your car you will wonder why you ever thought the rolling road would be able to keep the car stationary

99.9% of us don't really need a defence mechanism against a serial killer who is specifically murdering women in Ipswich, though. But 100% of us should keep some respect for the greiving families, and those in fear of being next.

No (with respect to the movement or otherwise of the plane) there is no difference at all between the cushion of air the hovercraft sits on and the perfectly free-wheeling castors the plane rests on. And the treadmill, as I've said numerous times and seemingly everyone else is assuming, IS POWERED. It's not a hamsters wheel (if it was, the plane would do big loop-the-loops while the wheel remained perfectly still)...how you could ever drive a treadmill using the wheels of a plane (which ARE NOT powered) anyway?

I think the people saying it doesn't fly are imagining the plane sitting stationary, with the treadmill running faster and faster until all of a sudden the plane floats away like a hot air balloon, and think that is what the 'does fly' folk are saying will happen I don't think you do quite get that 'the wheels aren't powered' results in it not making any difference what the treadmill does. A car would be stationary on the treadmill, but a plane would not be. Could a hovercraft move along the treadmill? Why is that any different....?

No! And of course it's motorised. Just before it does so - all speeds here are RELATIVE TO A STATIONARY POINT - The plane is travelling at 180mph in one direction (having accelerated up to this speed along the length of the treadmill), the treadmill is moving at 180mph in the opposite direction, the wheels are spinning as though the plane was doing 360mph (relative to the surface of the treadmill, it is) and then the plane takes off. Because...the....wheels...on....a.....plane....aren't.....powered......:banghead:

Why? The wheels are not what is driving the plane forward... Think of it this way: Could you safely LAND the plane on the treadmill? Or would the plane instantly stop the second it touched down with its (frictionless, freely-rotating wheels)? Where would the force come to stop the plane? Because it's the same force you think stops the plane from moving forwards in the first place. Or, make the equivalent assumptions that the wheels are locked but the tyres are perfectly slick. Do you think the treadmill will still keep the plane stationary, or will the plane just skid forwards under the thrust produced by the engines?

It is ambiguous, not very well worded. But following it through if you interpret 'speed of the wheels' to mean rotational speed then do you not have logical consistency - you end up with the treadmill immediately moving at infinite speed (and the plane still takes off). You should take it to mean the speed of the wheel axle (= speed of the door = speed of the nose = speed of any part of the plane but describing it thus does not you stuck thinking about irrelevant wheels and treadmills). To put this another way, when you are driving at 60mph, how fast does your rear view mirror travel? Your aerial? Your wheels.....?

My bold - small point but given frictionless wheels as we are here, the car would just sit there as the turntable spins underneath. But the minute you push in either direction it moves just as easily as though it were on the ground. Frictionless wheels also mean the treadmill doesn't have to any longer than a normal runway at all and that you don't have to worry about bearings wearing out. As well as being confounded by seaplanes, people who believe the plane does not take off presumably also believe that once in the air, a plane cannot accelerate any more and must glide to it's destination. And that helicopters cannot fly at all

That's right, but I can't work out whether you are saying it will take off or not :confused:

That's what I reckon too. I think a lot of these claims get thrown out due to people not being able to show.

BTW a very good book that is one third on the subject of the stupid and accidental criminalisation of cannabis is 'Reefer Madness', by the same bloke what wrote 'Fast Food Nation'. The other two thirds are about pornography and illegal immigration, so there is something for everyone (the connecting theme is exploitation within the black/grey economies at the margins of society): Amazon.co.uk: Reefer Madness: ...and Other Tales from the American Underground: Books: Eric Schlosser I accidentally put my copy next to a copy of the Daily Mail and the two annihillated in a blinding release of energy...

of course I was being sarcastic!

....knowing these scum are off the streets: BBC NEWS | England | Cannabis chocolate trio convicted (:thumbdwn: )

On the forum I got this off, someone initially maintained it would not fly and then finally clicked the right answer by giving the (relevant) example of "...a toy car on a record player turntable. Hold the car with your hand; you can easily push it forwards and backwards. Then switch the turntable on....you can stilll move the car forwards and backwards just as easily" Then a few post down he changed his mind again, saying "Hang on I was wrong before - there is NO WAY you could move the car against the direction of the turntable!!!" :confused:

There's an important difference between a plane and a car with wings....where is the acceleration developed?

Replying to each statement in turn: wrong, wrong, wrong, wrong, dunno (bet he didn't attempt the record on a giant treadmill though). You know there is such an invention as a sea-plane? How do they ever take off?

Winder on Clouseau, but the plane moves if and only if the engines power it forwards. It doesn't actually make any difference in which direction the treadmill runs, or at what speed.

All right, call it a 'conveyor belt' if you want, doesn't make any difference

Depends on whether you think the plane travels down the (runway-sized) treadmill , or not.

You've all got the wrong answer precisely because you are thinking along these lines. The wheels of a plane rotate freely, they aren't driven. It's not at all like running on a treadmill, or driving on a rolling road etc etc. Unless you are driving the original jet-powered Batmobile

Read the text, the treadmill is as long and as wide as a normal runway. The picture is not to scale Yes it is, because it is not explicit what it means by 'same speed as the wheels' - same speed as the axle, or the rotational speed of a point on the surface? But only one interpretation gives rise to a logically consistent situation, the other falls over. Other unstated assumptions are: Frictionless wheels, perfectly grippy tyres, zero meteorological windspeed, the mass of the plane stays constant even fuel is burnt, the treadmill updates its speed instantaneously and perfectly accurately etc etc. Normal type assumptions. It's good enough for people to get what is meant though