Skill's weekend teaser

[raysor]

Relative to the moving conveyor belt. LOL. raysor, you crack me up. Really. I just hope everyone else appreciates your sense of humour, I know I do.

Here's the killer.
Would the thrust, or whatever it is, shooting out the engines be stationary or travelling at x+ ???

PS. I know you're just gonna have an answer!

 

[TheBramble]

Thus we see that the speed of the conveyor is quite irrelevant to the speed of the frictionless aircraft

Not according to Skills. He says the speed of the aircraft is directly related to the speed of the conveyor. Exactly related. When one starts to move one way, the other moves the other in direct and opposite proportion. We don't know how or why, we just accept Skill's constraint. THey cancel out.

+X-X = 0 = Plane does not move = Plane does not take off.

 

[TheBramble]

Here's the killer.
Would the thrust, or whatever it is, shooting out the engines be stationary or travelling at x+ ???

PS. I know you're just gonna have an answer!

The thrust moves the plane. As the plane moves the conveyor also moves - in the opposite direction - thus canceling exactly and precisely any forward motion relative to any fixed reference point.

 

[peto]

Skills said "The belt has the same dimensions as a runway at an airport*, and is set up to exactly match the speed of the plane's wheels".
I understood that to mean that the belt runs at the same speed as the rubber at the base of the wheels (although it doesn't have much choice!). The plane can move at quite a different speed.

Makes no difference anyway. The conveyor can run at a 1,000,000mph backwards for all I care, the plane will still take off albeit with some remarkably fast spinning wheels under it!

 

[raysor]

Ok nearly next weekend, but I'll throw in my hat to try to end the misery. The plane takes off normally.

We must make two assumptions however which is not in the OP, one is that the wheels rotate with zero friction (i.e. the brakes are off and the bearings are perfect, so that the lightest of touch on the plane will make it move forward); the other assumption is that the inertia of the wheels spinning is negligable in relation to the inertia of the plane, with it's far greater mass.

If we suppose the conveyor is now tugged sharply towards the rear of the plane, then the plane will not move. It weighs many tons, and it's inertia will cause it to remain quite stationary, although its wheels will turn to keep pace with the conveyor (in reality there is always friction, so the plane would slowly start to move backwards until, after some considerable time it would reach the conveyors speed). Thus we see that the speed of the conveyor is quite irrelevant to the speed of the frictionless aircraft; only its wheels will move.

Now let us imagine the pilot starts his engines. The thrust created will cause the plane to begin accelerating relative to air, and it will take off in the normal way regardless of its wheel speed.

All clear now?

Good effort, but mostly irrelevant

 

[TheBramble]

Skills said "The belt has the same dimensions as a runway at an airport*, and is set up to exactly match the speed of the plane's wheels".
I understood that to mean that the belt runs at the same speed as the rubber at the base of the wheels (although it doesn't have much choice!). The plane can move at quite a different speed.

Well THAT would be interesting.

At what point do the plane and its wheels meet up again? Hopefully sometime before landing…..?

I kinda hoped they’d stick around on the bottom of the plane for a little while, You know, just a comfort factor thing!

Makes no difference anyway. The conveyor can run at a 1,000,000mph backwards for all I care, the plane will still take off (albeit) with some remarkably fast spinning wheels under it!

If the conveyor is running backward at 1,000,000 mph then the plane’s wheels are running forward at 1,000,000 mph. Has to. No other way under the constraints imposed by Skills.

 

[raysor]

The best solution would be to call it a draw.
In the spirit of Skill's teaser; the plane will take off as normal.
In the pedantacism, if that's a word, of Bramble's and to a degree mine also: If the wheels are always in sync with the belt then the belt and wheels might just as well be stationary because, surely that means there can be no forward movement!!

 

[peto]

The wheels are fixed on the plane, I hope!

If the conveyor is running backward at 1,000,000 mph then the plane’s wheels are running forward at 1,000,000 mph. Until the pilot fires up the engines. Then the wheels speed and that of the conveyor increases to 1,000,100 or so and the plane prepares to lift off. The wheels spin frictionless below the aircraft and so have no influence on its airspeed.

 

[TheBramble]

The best solution would be to call it a draw.
In the spirit of Skill's teaser; the plane will take off as normal.
In the pedantacism, if that's a word, of Bramble's and to a degree mine also: If the wheels are always in sync with the belt then the belt and wheels might just as well be stationary because, surely that means there can be no forward movement!!

A draw?

The bloody plane either takes off or it doesn't. How can it be a bloody draw???

As you've underlined - there is no forward movement. The plane doesn't take off.

You're not a troll, are you. You're quite serious. This is frightening.

 

[TheBramble]

The wheels are fixed on the plane, I hope!

If the conveyor is running backward at 1,000,000 mph then the plane’s wheels are running forward at 1,000,000 mph. Until the pilot fires up the engines. Then the wheels speed and that of the conveyor increases to 1,000,100 or so and the plane prepares to lift off. The wheels spin frictionless below the aircraft and so have no influence on its airspeed.

Aaaaarrgggghhhhh.............!!!!!!!!!!!!!!!

You suggested in your previous post the wheels could move at a different speed to the plane. If they could and if they did, they would be somewhere other than the plane, wouldn't they.

What is all this bollox about the pilot ‘firing up the engines’. If the engines are not on, there’s no thrust, therefore no forward movement from the plane and therefore no backward movement from the conveyor.

Have you and raysor just got back from the pub….?

 

[peto]

Well THAT would be interesting.

At what point do the plane and its wheels meet up again? Hopefully sometime before landing…..?

I kinda hoped they’d stick around on the bottom of the plane for a little while, You know, just a comfort factor thing!

If the conveyor is running backward at 1,000,000 mph then the plane’s wheels are running forward at 1,000,000 mph. Has to. No other way under the constraints imposed by Skills.

It might help you to imagine the plane landing on the conveyor with no wheel brakes. No matter how fast the conveyor runs or which direction it runs in, the plane will touch down normally, and will only slow down if the pilot uses reverse-thrust. When the pilot finally stops it a small child stood on the grass holding the wing-tip will be able to hold it steady while the passengers alight (hope they use an airbridge!)

 

[raysor]

The wheels are fixed on the plane, I hope!

If the conveyor is running backward at 1,000,000 mph then the plane’s wheels are running forward at 1,000,000 mph. Until the pilot fires up the engines. Then the wheels speed and that of the conveyor increases to 1,000,100 or so and the plane prepares to lift off. The wheels spin frictionless below the aircraft and so have no influence on its airspeed.

You are forgetting that the wheels can move in two ways: About their axles (or roundways) and also horizontally forwards (or backwards).
It's a red herring. The wheels and the belt could be stationary. Therefore the only way forward is for them to break contact with the belt.
If there is proof contrary to that then me and Brambles can be taken out and shot.
If I've got this wrong then I am either an idiot or I am missing something pretty fundamental.

 

[wasp]

Indirectly, this has been one of the most informative thread regarding trading and behaviour for ages.

I couldn't give a toss if the plane takes off, but do wonder why they'd put it on a conveyor belt in the first place?

 

[peto]

You are forgetting that the wheels can move in two ways: About their axles (or roundways) and also horizontally forwards (or backwards).
It's a red herring. The wheels and the belt could be stationary. Therefore the only way forward is for them to break contact with the belt.
If there is proof contrary to that then me and Brambles can be taken out and shot.
If I've got this wrong then I am either an idiot or I am missing something pretty fundamental.

That's why I suggested that an assumption had to be made that the wheels were frictionless. otherwise the conveyor will tend to slow the plane a little, but probably not enough for it to reach take-off speed.

 

[TheBramble]

It might help you to imagine the plane landing on the conveyor with no wheel brakes. No matter how fast the conveyor runs or which direction it runs in, the plane will touch down normally, and will only slow down if the pilot uses reverse-thrust. When the pilot finally stops it a small child stood on the grass holding the wing-tip will be able to hold it steady while the passengers alight (hope they use an airbridge!)

Great idea. Let's modify your spurious example and give it the same constraint at Skills sets for his teaser. The wheels of the plane when in contact with the conveyor will (MUST!) run at exactly the same speed, but in the opposite direction.

As the plane’s wheels touch the conveyor they’ll be going at about 120 mph (747 with full flaps and slats). The conveyor will immediately go at 120mph in the opposite direction as per Skills’ edict on the fixed relationship between plane’s wheels and conveyor belt. And the plane will stop dead relative to any fixed reference point.

Economy will now get an immediate and violent upgrade to Business class, Business class will find they are now in First, and First will be helping the Captain and co-pilot retrieve their soft tissue from the inside of the windshield.

Yes, a ridiculous scenario and one unlikely ever to occur in reality, but theoretically, according to Skill’s teaser as set, this is what would happen in this scenario you suggest.

And useful in perhaps jogging some folk out of their stupor that there ‘needs’ to be or ‘must’ be any semblance of normal physics involved. This is a teaser. It is designed to throw logical thinkers off. It’s done that.

Even so, the majority still got it right based on poll data.

I’m not sure where Mr. G ended up as he eventually came round to my way of thinking (good for him) then stormed off in a bit of a huff for some reason. That’s boy has had so many turnarounds on this I’m sure he’s going to need a neck-brace.

 

[peto]

Indirectly, this has been one of the most informative thread regarding trading and behaviour for ages.

I couldn't give a toss if the plane takes off, but do wonder why they'd put it on a conveyor belt in the first place?

Well I tried. Beddybyes time for me, I will not contribute further. I unwisely thought I was clever enough to simplify the problem and make the answer clear, and I admit to failure in that regard as any further posts I could make will only muddy the waters further.

I guess there may be trading parallels, entrenched opinions holding on to positions no matter how strong the evidence .... sounds familiar? Or maybe the difficulty in tutoring trading. Bramble, I don't say whose opinions here are too entrenched, yours of mine

I liked the idea of conveyor belts, good lateral thinking, if perhaps a little impractical .

 

[Atilla]

Isn't this a little like a body running on a jogging machine. :whistling

No movement but pure waste of energy.

Wheels and conveyor belt turn in opposite directions. Action and reaction equal and opposite. All energy absorbed nothing else left. :smart:

Plane remains static! :idea:


Forgive me if this has already been mentioned but couldn't bring my self to read umpteen pages scientific blogg. :-0

At least now I have something to read over the weekend... :cheesy:

 

[TheBramble]

Bramble, I don't say whose opinions here are too entrenched, yours of mine

I don't have an 'opinion' on this peto. I just did the math....

 

[TheBramble]

Plane remains static! :idea::

At last, company.

I'd like to think we're in the Elite mate, but seems we're just part of the (very bloody silent) majority.

 

[Atilla]

At last, company.

I'd like to think we're in the Elite mate, but seems we're just part of the (very bloody silent) majority.

So what's our prize? :clap::clap::clap: