If a jumbo jet is on top of a huge conveyor belt that was programmed to move backwards at the same speed at the jumbo's wheels moved forward, would the jumbo be able to take off?

No, because there would be no air flowing over the top of the wings to provide the force to allow the plane to take off. Surely?

If however, there was a big fan in front of the conveyor belt, blowing air at the plane at the same speed as the belt, it would. It would then hover in place, as seen from the ground. Also, if you had people holding cut-out clouds on sticks, and running past the place, that would be cool.

Oh Christ. This one blazed for months on YakYak, and most people on YakYak are scientists.

Would it not move, then?

Assumption: the wheel brake is not engaged.



Would have no effect.



Yes because the engines work on the plane body, not on the wheels, where only a minor opposing force would be encountered due to the friction located at the wheel centre.

Thread over.

MR CONCLUSION FACE, so to speak.

No. At least not as you have stated the question there (with the conveyor matching the speed of the wheels) as soon as the plane achieves any forward motion the rules of the question are broken as the belt can no longer be matching the speed of rotation of the wheels. That wording of the question gives an impossible scenario.

MR D IS CORRECT FACE.

Can we lock this please before anyone starts being "clever"? (It's for your own good: several people died by my hand before the one on YakYak got done).

It would if it was a Jumbo Harrier.

VTOL FTW!

Indeed. The powered motion isn't being provided by the wheels, so the treadmill is irrelevent. A car, on the other hand, would go nowhere.

Unless it was the batmobile, or the Mean Machine.

(Both of which I believe can fly, incidentally.)

must resisstt... SNAP..

A) Yes air would be flowing, because the plane would be moving forward.
B) That's not how plane wings work anyway.

Yeah it takes off, naturally, because the wheels arent powering the forward motion of the plane and therefore what is (the jet engines) arent influenced by the treadmill.

Hey there, Kalmar, I'm Kamineko on Yakyak, and you're absolutely right, the thread wasn't fun.

It's like if you're running on a treadmill. If someone ('the engines') shoves you in the back, you'd go off the front of the treadmill, irrespective of the motion of your legs on the floor.

I know, hi

Does the Pope shit in the woods?

If the treadmill sped up to match the speed of your legs, you'd stay still though, non?

No. You'd fall on your face then fly backwards.

Your feet would move back due to the contact force of the treadmill, and your back would move forwards due to the engines. You'd rotate and fall on your face.

However, if you were Johnny 5, and your track mechanism were 'frictionless', you'd go forwards.

Under ideal conditions, a 'frictionless' wheeled vehicle will remain at rest on a treadmill moving in the direction of the wheel track until acted on by an external force. (High amounts of friction would result from a force acting perpendicular to the wheel track. But you don't got that.)

SORRY BUT NO, HE ISN'T FACE

As soon as the plane moves forward the 'rules' of the question are broken. The question is a paradox.

Oh holy fuck.

Get roller skate.

Put roller skate on treadmill.

Start treadmill, place hand at rear of rollerskate.

Push rollerskate enough so it stay in position on treadmill.

Now, increase speed of treadmill.

Force required to maintain position of rollerskate on treadmill is the same.

Now, push rollerskate forward.

Plane takes off.

http://www.scrapheap-challenge.com/view ... t=conveyor

The question wording is trying to apply too many constraints to the system at once. If you like, we can just assume that's Grim... being silly while copying out the question.

If the treadmill surface was moving in an equal and opposite direction to the plane body (which is a reasonable and physically possible interpretation of the question stated) then there's no paradox.

why? why?

this reminds me of people throwing oranges at a basket while skiing of my physics exams.

What about if there was 1G of centrifugal force affecting the plane's wings in the bipolar direction? Then there'd be a case for it not being able to take off.

YOU ARE WRONG, AND YOU HAVE A GROTESQUELY UGLY FACE

The 'rules' refer to the speed of the conveyor belt matching the forward speed of the wheels, in reverse. If the wheels move forwards at 10 mph (relative to a point which is not moving at all), then the conveyor will "match" that by moving at 10mph in the opposite direction.
So, the wheels will "see" 20mph, but the plane will be moving at the same speed, regardless (less a very small amount for the additional rolling resistance and bearing friction).

I agree though, the question is expressly designed to cause the maximum amount of differing interpretation and argument

Assume away, it's just I've seen both versions of the question so I was answering the one which Grim...'s most closely resembled.

It would topple to the side.

I said forward speed of the wheels, not rotating speed, so neeeeeer!

Then yes, of course it will take off. What's going to stop it?

Confrontational FTFY.

Nothing. GOTO 20

Naomi Campbell getting shirty about a lost bag.

Now, on the other hand, if you're standing on top of a truck and you ju...

DON'T BE AN IDIOT. There's no such thing as a centrifugal force.

I didn't say which side.

The passengers would jump out of the plane and beat Grim... to death with hammers for setting up such a RIDICULOUS PARADOX (you swine!)

The argument proposes an unphysical situation.

Firstly remember the engines of the plane have nothing to do with the wheels. If you had the plane sitting on the runway without any wheels and it tried to take off, you would take off (assuming the plane didn't rip itself apart as it dragged itself along the runway). The wheels are just their to act like ice as it were.

With that in mind, you then the proposition is a situation where you've fixed a free spinning wheel to the bottom of this plane, on a conveyor belt that is matching it's spin.

Now as we know the plane will move forward and take off we have a situation where these two surfaces (the wheel and conveyor) will endlessly, exponentially, increase in speed. Which is unphysical.

In real life the jumbo yet would start to take off (making forward progress) whilst the wheel and conveyour quickly melted. Then the plane would drop onto the runway and rip itself apart on the now fucked runway.

But in real life the unphysical situation with the conveyour and wheel can't be achieved, so the plane will lift:

But did mythbusters see that?

youtube]YORCk1BN7QY[/youtube

EDIT: I broke the link as it seems The Overlords have taken down all the Mythbusters clips.

I guess we'll never know!

That's not what the original post says.

"programmed to move backwards at the same speed [th]at the jumbo's wheels moved forward"

The wheels are attached to the plane. They move forwards at the same speed as the plane. OK, they are rotating, but that has nothing to do with the question.

http://www.youtube.com/watch?v=4owlyCOz ... re=related

There.

Re: the paradox.

It isn't.

Wheel moves left at 10 m/s, belt moves right at 10 m/s, wheel spins very quickly, but the plane moves.

Anyone who says different is trying to be awkward.

The wheels on a car that power it are fixed to turn at the rate the engine makes them. That drives it forward. They are on a fixed axle.

The wheels on a plane are like those on a toy car. They are free spinning. As such they spin at the rate the plane is pushing it forward along the tarmac. Like a finger pushing a car. That speed is slow enough that the friction doesn't melt the ball barings in the wheel.

The same wheels on a conveyor belt will speed up as the jet moves forward. But the convayor belt is also speeding up, so the wheels never reach a balance and continuously increase in speed. Soon enough the friction is beyond what the wheel and belt can take and they melt.

All the while the plane is continuing to take off.

Get me?

The conveyor belt on that video doesn't increase speed to match the speed of the plane.
Also, the plane appears to be tied up with string.

Also this assumes that the wheels wouldn't 'slip'

Imagine wheels made of ice.

Ice wheels.

They would eventually just slide over the conveyor.

Just because rubber doesn't seem like ice to us, doesn't mean the same thing wouldn't happen when it's attached to a jet engine.

No, because the maximum speed of the conveyor only has to match the forward speed of the plane (and the wheels of the plane), in the opposite direction. So the wheels will have to turn at twice their normal speed, not "infinity faster" or anything like that. They will most probably survive this, so melting runways and the like simply don't come into it.

You've inserted "spin" (rotational speed) into the question, and it's not there. The "speed" is therefore the linear directional travel of the axle, which is the same as that of the plane.

And yes, I know the plane will take off.

Lots of snakes would burst out of crates and Samuel Jackson would save everyone's mother fucking ass. Obviously.