Be Excellent To Each Other

Stop being silly now, please.

I'm sure you're playing Devil's Advocate, but do you also believe that if a plane came in to land, and it was to land on one of these magical treadmills, that it would stop instantly when it touched the ground?

What are you on about? I've never once said what I think would happen, just that that video proves nowt.

Grim... does: he started the thread. We do: we replied to the thread.

Man, this thread is fully of easy questions! I'm on a roll! (At twice my normal speed, to boot.)

Oh God, certainly not. I just wanted to give you all something to talk about.
There has been a surprising lack of 'no' people, however.

Oh holy fuck.

Get roller skate. (This is the plane)

Put roller skate on treadmill. (treadmill is runway)

Start treadmill, place hand at rear of rollerskate. (this is engine thrust)

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. (wheels rotate faster to match speed of treadmill

Now, push rollerskate forward. (increase in engine thrust,)

Plane takes off.

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

I don't think the plane would take off. On the assumption that the treadmill automatically and instantaneously matches the moving speed of the plane at all times, there would be no net movement in any direction. It doesn't matter if the rockets blast the living shit and the wheels move at 200mph, if the treadmill is constantly keeping up, there still isn't any net motion.

Both forces are equal, there is no wind resistance (as per me running on treadmill vs. running outside), thus no air is moving over the wings and the plane would not be able to propel itself upwards. The end.

Yes, that's encouraging, it's a good gauge of a forum, so well done. It will continue to re-spawn people who will only read the first post and fire off their answer forever though, be warned.

The "intentionally altering the question" people are also yet to be pacified

Ya should'a picked something else if you wanted a debate. This isn't a debate, it's a pretty simple easily analysable theoretical situation.

Funny as it is to watch you all self-destruct with rage - I'm going to be serious for one moment.

There is no fucking way that's true, unless you've invented magic wheel bearings.

If you can have a conveyor belt of infinte length, I can have frictionless wheelbearings.

If he gets a 'huge' coveyor belt as he mentioned, you get 'near frictionless' wheelbearings.

I'll be wanting them all back when you're done playing though.

Why would you need an infinite length conveyor?

Providing conveyor belt is long enough for plane to reacht ake of velocity, then, yes.

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).



Not the end, because the plane will move forward (see above) and will therefore take off as normal. Also, that's not really how wings work anyway but let's not get into that just yet.

In fact, if the plane isn't going to move, it only needs to be a hundred feet long MR WINKY TONGUE FACE

Oh, we did have a 'no'. I didn't see that.

Plane will move as per rollerskate in my original response.

Well he makes the conveyor belt go faster than the plane once he initially gets them matched and it just sits in position, which is good enough for me. I agree, though, that doing it with a proper jumbo jet, no strings attached (hur), is the way to go -- I've got 42p, half a polo and bit of pocket-lint on me to get the fund going.

Well, it was after your post, to be fair (see what I mean about the re-spawning?). Unless we're assuming telepathy as well, which wouldn't surprise me.

That's what made me think there was cheating afoot.

If there is no net movement, there is no wind. If you were standing at the side of this stationary plane would you expect to be blasted by winds? Of course not, nothing is moving anywhere. That being the case, how could it possibly take off?

I have forwarded this question to a mate of mine, who got five A's at A level, including Physics, has a 1st Degree in Physics, and currently works at CERN doing a physics PHD in Geneva, so fuck whatever any of you think, I'm going to agree with whatever he says even if it's the opposite of what I just said

I'm going to Malta in 2 weeks.

He's probably never going to speak to you again, comical.

Maybe his brain will melt, or something.
OH NOES COMICAL, WHAT HAVE YOU DONE?

Please read the responses again. Not reading the responses = trolling

There is "net" movement, the plane does move forwards on the conveyor belt. Just as if the conveyor belt wasn't there.
So there is "wind", so there is takeoff.



He'll probably say it's a rubbish question.

Get roller skate. (This is the plane)

Put roller skate on treadmill. (treadmill is runway)

Start treadmill, place hand at rear of rollerskate. (this is engine thrust)

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. (wheels rotate faster to match speed of treadmill

Now, push rollerskate forward. (increase in engine thrust,)

So forward movement of plane causes lift in the wings.

Funny as it is to watch you all self-destruct with rage - I'm going to be serious for one moment.

There is no fucking way that's true, unless you've invented magic wheel bearings.

Cynic.

And this is spamming, leave it ahht!

It's down to whether the wheel will slip against the belt. If there is no slip, then there can't be a situation of balance between the wheel and the belt due to the presence of the engine acting on the plane.

So at every instance of time the wheel and the belt match each others speed but the speed at which they match is increasing.

I have read responses I just disagree about the net movement part. Net speed relative to the motion of the treadmill, yes, net movement relative to a stationary point, no.

Again, I'll await the expert answer, because most of us are physics-worthy morons relying on speculation (myself included) from what we reckon is correct.

Personally, I still can't see how the FUCK a clock on a moving train will not keep time in the same way as a person standing still watching the train holding an identical clock does. Special Relativity, or something? Christ knows, I got an E at A-level physics (but at least I did it, bitches).

I'm doing a PhD in Astrophysics,after a masters in Physics does that count?

(Arguments from authority suck though).

For the love of God, don't ask Mr Resonance Cascade -- he'll kill us all!

Would that be so bad?

My mate is far far smarter than me, so I'm going to trust whatever he ends up saying.

It's like that Bill Bailey quote, which I can't remember properly that goes something like, "I'll believe the opinion of anyone I think is a bit smarter than me".

Edit: cheers google:

"I am a Relaxed Empiricist. An Empiricist demands proof of knowledge. I am a RELAXED Empiricist, which means that I only believe something to be true if someone I know quite well tells me that's pretty much what happened."

I'm sorry to do this, but that statement "isn't even wrong", because it makes no sense.

No slipping is involved. By the way, "slip" is a well-used term amongst automotive engineers regarding the behaviour of a steered wheel in a turn, and is not what you're suggesting here (loss of traction).

your diagram:

[/quote]

Here's the point just before the plane leaves the runway (let's say). So, what speed is the wheel subject to? If your answer is any different from 200m/s, you'll need to prove it

But there is nothing to prevent movement relative to a stationary point (other than a small increase in drag from the doubled ground speed, so there will be movement.

*looks at first post, reads question*

ABANDON FORUM!

I'm liking this. I may well be wrong. Don't worry.

I'm using slip to me that the rather than the wheel rolling across a surface, indeed it loses traction and it slides across a surface instead. In the way that a plane with it's brakes on would still take off, as eventually the force would overcome the coefficient of static friction between the tarmac and the rubber tread, and it would slide forward.

I'm saying that when interpreting this question people persume, that this slide can't occur, and as such the resistance between the wheel and the belt is sufficient to hold back the force of the jet. Which of course it can;t.

But I need to think about whether the rotation of the wheel keeps increasing or reaches a constant.... Hmm... I need a pen....

EDITED TO WHAT I MEANT.

As far as I can see the following is correct:

1) The Engines provide a force to move the plane in this ---> direction
2) Friction causes the wheels to move around and normally the plane roles forwards
3) The treadmill provides a force to the wheels in the opposite direction (that's this <--- way)
4) If we are to assume that the plane stays in the same place, then the forces must ballance.
5)The jet is pushing one way, the treadmill is pushing the other. There is no net force, so there is no acceleration.
6) Lift in a plane, is provided by fast moving air passing over the wing, the shape of the wing means that air travels faster over the top of the wing compared to the air on the bottom of the wing.
7) Faster moving air has a lower pressure than slow moving air, and this causes lift (the high pressure air rushes into the low pressure air [just like the high pressure air in a balloon rushes out into the low pressure])
8) As far as I can tell then, the only thing that determines if this jumbo is going to take off or not is the speed of the air over the wings.
9) There is no air flow over the wings, the plane does not fly. This is why Boeing (and even car designers) have giant wind tunnels instead of giant tred mills.

I would love to be proven wrong tho.

Malc

Vast numbers of bananas for Malc for agreeing with me (I think).

.

I also have a degree in Physics.

It has to move forwards, as there is nothing preventing it from doing so. I don't wish to resort to the rollerskate on the treadmill argument again (but I will); you are saying that no matter how strong you are, you would never, ever be able to push the roller skate forwards even a nanometre. Not even if you got a JCB and tried to push the rollerskate forwards. Or a million JCBs, etc.

In essence, you are saying that a treadmill acting on free-running wheels can exert an infinite force on a plane.

Which it can't.

Ergo, it can take off.

I think so too.

I did 2 years of a physics degree in the early 90s if that helps

Malc

You are wrong malc.


You are assuming that the friction between a belt and wheel is sufficent to stop the plane taking off.

What would happen if the wheels were made of ice? They didn't spin they would just slide.

Would the plane take of then?

What's the difference here apart from the fact that a rubber wheel is slightly stickier.

There is no reason to assume that. If you assume that, then the plane obviously can't take off, so there is no point in going any further.


The jets have hundreds of thousands of pounds of thrust, the treadmill can only exert a few tens of pounds (for a given speed) due to the rolling resistance and wheel bearing drag. So there will definitely be acceleration.


No, it isn't. Some lift is provided that way, but it would never take off if that was all.


The speed of the air past and against the wings, correct.


There is air flow over the wings though, see above.


Happy to help

HAND ON ROLLER SKATE PUSHING SKATE AGAINST TREADMILL




AS TREADMILL SPEED INCREASES, WHEEL SPEED INCREASES, THRUST NEEDED TO HOLD PLANE IN ONE PLACE IS CONSTANT AS THIS IS YOUR HAND AGAINST THE SKATE ON THE TREADMILL, YOU DON'T NEED TO PUSH ANY HARDER


INCREASE THE THRUST PLANE MOVES FORWARD

5) Lift in a plane, is provided by fast moving air passing over the wing, the shape of the wing means that air travels faster over the top of the wing compared to the air on the bottom of the wing.
6) Faster moving air has a lower pressure than slow moving air, and this causes lift (the high pressure air rushes into the low pressure air [just like the high pressure air in a balloon rushes out into the low pressure])
7) As far as I can tell then, the only thing that determines if this jumbo is going to take off or not is the speed of the air over the wings.
[/quote]

AIRFLOW OVER WINGS AS PLANE MOVES FORWARD



I really don't mean to keep harping on about the roller skate, but it is the best model.

Apologies for caps and poor formatting.

This said something about assuming something in point 4 before.

Here is the oringal question

I assume what is meant by the speed of the conveyor belt is the same as the speed of the wheel, that if you were standing still next to this conveyour belt then the plane would be stationary relative to you.

I am also assuming that the plane is doing exactly the same thing as it normally would when trying to take off from a normal runway.

Malc