Imagine a plane is sitting on a treadmill

It is pulled by something. Usually another airplane. Duh!


Actually, that is the most relevant part. Especially since the original original (not DW's, but the oldest known) had it matching the speed of the wheels which is a totally different situation and what has soo many people confused.

The most irrelevant part is the jet engines. It matters not where the propulsion comes from. Like I said, the wheels could even be powered like a car (the plane might need to be smaller though).

If you can't show where the energy goes as per the first law of thermodynamics everything else is a waste of time because the plane will not be slowed down.

Edit: the post is Imagine a plane is sitting on a treadmill, for those who haven't seen it.

I just went out and walked around downtown for an hour or so amongst thousands of people who do not know that this discussion is going on and I thought about planes and treadmills and friction and matchbox cars and jet engines and the laws of physics and such and did not freak out once at the xmas madness that has our fair city in its grip.

Thank you TT.

I've just been down the pub and I'm ready for round 9. So which of you daft bastards think it won't fly? After a couple of lager tops it seems abundantly clear that it will fly. And how.

You are single with a cat too aren't you?

If you don't know that it matters not one iota about the jet engines, then there is no helping you.

Oh dear. And you're a scientist?

Edit: if you can't answer the question, you have lost the argument. The only other thing you can do is disprove the first law of thermodynamics. Good luck if you decide to try that.

Got a reference to this?


Of course it makes a difference. If you are reading the question as "the treadmill will turn at the same speed as the vehicles wheel speed" then:

For a car:
It will speed up with the cars wheels until you reach the maximum speed of the car (Max engine revs in top gear)

For a plane:
As discussed many many times, the belt will have to accelerate at impossibly stupid rates of acceleration in order to disspiate the surplus energy into increasing the angular velocity of the wheels (the only place the energy can go) until the speed of the belt is high enough to create airflow of its own.

And your avoidance of the energy question really is showing that you are not getting the problem at hand.

Some planes don't have jet engines.

The plane could be pushed by a car. You do know that right?

Sure, we can pull it with a car if you like. But to make the analogy err... analogous, the car would be in *front* of the treadmill (not ON it) and have no trouble* pulling the plane.

*assuming the car is powerful enough for this

@ eurovol

Doesn't make any difference. The plane gets energy from its engines, be they jets, props, or whatever. In order for the plane not to move, the energy from the engines has to go somewhere (first law of thermodynamics - conservation of energy).

We argue that the energy goes into moving the plane as per Newton's third law.

You are arguing? What? Where does the energy go? Into the treadmill? How?

I hate to say it, but I can see what Eurovol is getting at. Assume take off velocity is 200mph and your plane is driven like a car until it takes off. If the belt is moving at 200 mph you could accelerate your car to 400mph and reach take off speed. The driven wheels are rotating at 400mph, but the car is moving at 200mph relative to a static observer, so you are still satisfying the criteria of the question. oder?

Actually, a really good way of describing this is a car accellerating, pulling the plane on a rope. The car is off the treadmill, and the plane is on it. No matter how fast the treadmill goes, the plane will accellerate with the car.

@ SP

No. Where does the energy of the engines go? It's go to go somewhere, energy does not simply disappear. It cannot go into the treadmill because the wheels are not driven and cannot therefore transfer any energy.

I think you misread my post. I was referring to a case of a plane with driven wheels, being able to take off. Bit of a silly mind game really, and there still remains the fact that you can easily have a belt that prevents car from moving forward, but not one that can keep a jet stationary.

Possibly.

*sigh*

There's no question the argument is won. Some people just refuse to admit it.

Well I thought about it, wasnt sure, looked it up in case there was some trick I was missing, and it turns out I was right. Has it been officially answered yet? Seems like it has but I dont know what people are arguing about.

sGb27 summed it up:

Ok now I am not sure. The thread I used to check my answers was just like this one. I think it will take off, but I didnt work that out by removing my assumptions, in fact I assumed several things. That the conveyer belt wont be able to keep the plane stationary (yet will cause the wheels to revolve twice as fast as usual, but this is I think irrelevant), as the plane is not driven by its wheels pushing (inefectivley) against the belt but rather by its jet engines pushing against the air.

However, because I made those assumptions, and relied somewhat on my intuition and imperfect reasoning, rather than any facts or experienced knowledge on the subject, and because the issue is obviously non trivial, I have reason to doubt my answer, therefore I assume I have fallen victim to false reasoning, and that the plane will not in fact take off, for reasons that are unknown to me.

Ok someone give the proper answer, and explain it without assumptions.

Exactly. Even a car would move forward and could push a small plane or have a plane sitting on its roof. It is all in the wording of the question. It is the speed of the object's forward motion, not the wheels.

Ignore eurovol, he's beaten but refuses to admit it.

If you want to prove it to yourself, consider the following:


No non-fly people have even tried to answer these questions seriously.

According the flat-earthers this is what is happening to the energy:

The treadmill is going like the clappers (10,000mph or whatever) backwards, and because the wheels are not 100% friction free - the energy is being dispersed as heat and noise in the bearings and tyres of the wheels.

That is the only logic you can apply to their non-logical solution.

But it is like arguing about the existence of God with religious nuts. Deep down they know its a crock of shit, but will keep arguing until their deathbeds.

Elvis is alive and well, he killed Princess Di whilst riding the Loch Ness monster and piloting a non-flying plane on a 10,000 mph treadmill.

OK, this thing's been beaten to death.



Yes, I was trolling, and I enjoyed myself immensely. I realised it was dead-horse-plus-stick time when I re-read my lame attempt to fire up some more ranting by questioning the angle of attack. I could've done better.

The wheels have nothing to do with the airplane's speed; they're simply there to hold the thing off the ground so that the belly doesn't make sparks. It's been the red herring of the entire thought experiment.

For the people arguing about power and forces, the wheels and the belt cancel each others' forces out. What's left is a load of thrust from the engine which must push the plane forward. The plane won't remain stationary.

I still say that animation with the car which had wheels on top isn't a great representation of what's happens here, but there you have it.

That was a lot of fun, DW. Thanks. I lost it when I read about the conveyor moving so fast it would cause enough air to move that the plane could lift off. Sometmies I just love people who went to the University of MakeShitUp.

woof.

Damn. You were convincing up until the 'angle of attack' post. I still didn't twig though.

To be honest, I was a victim of this interpretation. I hadn't even read the thread when I first posted and basically answered based on this. I was wondering what the hell people were going on about with the wheels going twice as fast at the conveyor when the wheels could only go the speed of the conveyor.

Then I decided to fuck with the people who were going on about the fucking thrust and engines and rope and toy cars and planes on a threadmill and being generally biligerant.


You really are a fachidoten aren't you? A fucking car could even move forward. It matters knot about the means of propulsion.

A car is sitting on a conveyor belt and goes twenty miles an hour by its speedometer. The conveyor belt is going in the opposite direction of the car 10mph. How long will it take the car to go 10 miles? Now do you get it?

DW may be laughing at me for originally having the wrong interpretation, but I am sure he is laughing louder at the fachidioten having the right answer for all the wrong reasons.

PS: I think quite a few of the people have been posting on here to rile up the fachidioten.

That one was really lazy. Had I been less busy in the office I whould've written about how the angle of attack would negate any lifting effects of any wind caused by the belt moving so fast. I also really wanted to add a post about the plane "jumping" into take-off: Even if, by some miracle, the plane managed to get up, if would fall right back down because it was stationary and therefore had no airflow over the wings, but the time in the air would've allowed the jet to propel it a bit further forward and so it could perhaps bounce its way into the air. That could've been fun.


No, a car can't. A plane doesn't get its thrust from the wheels, it gets it from the propellers or jets. the wheels are there so the belly doesn't get scratched. All of a car's propulsion comes from the wheels which the conveyor belt matches. It's this concept that's key to the whole question of the plane.

woof.

Good try, but not falling for it.

I thought the inclined runway would get more play than it did, but I was too busy the last two days to push it.

Now your missing the point of Eurovols post (as i interpret it) which is to change the argument from one of physics to one of semantics.

If the belt is travelling at 'take off speed' there is nothing to stop me driving the wheels of my supercar to two times take off speed. The speed at which the car is travelling through the air is the same as the speed at which
the belt is moving. The wheels are travelling twice as fast. So what's the difference between this and the jet plane. Belt is moving at same speed in both cases , vehicle is moving through the air at the same rate and wheels are travelling twice as fast.

Edit - and as we all know Supercar can fly.

Car can't fly, but the plane attached to the roof can once it gets up to speed and the rope is cut that is used to tie it to the roof of the car so it doesn't fall off before reaching take off speed.

You cannot substitute a car in the place of a plane in the original question. It just won't work, at least not without redefining which speed the conveyor is matching.

If the car moves forward, the conveyor moves back. But, as soon as the conveyor matches the car's speed, the car is stationary, so the conveyor stops. But then the car is moving again, so the conveyor starts up. In the question all of this happens exactly simultaneously, which makes me say it doesn't work. Anyone else have a thought on that?

@eurovol of course it can...

'as well as its ability to fly, Supercar can travel underwater, on land with a ground effect cushion from its vertical boosters, and even go into space.'

Do you have to do this? It's fucking childish. Yes, I got annoyed with parnell and called him a name earlier. That was stupid and I apologised.

What you don't seem to follow is that this is possible for a car, you just have to adjust the treadmill to absorb 50% of the energy put out by the car's wheels.

On the other hand it would be impossible to stop a conventional plane with a treadmill, because planes don't have driven wheels and therefore there's no way to transfer the propulsion force from the plane to the treadmill without putting on the brakes, which isn't allowed by the question ('everything else is normal').

So there is an important difference between cars and planes in this respect. And a lot of others as well, but they are beside the point.

Of course it can. The conveyor matches the speed of forward progress no matter what is running on it. Hell, a guy on a skateboard could move forward and even a guy running the wrong way on a conveyor belt can move forward although neither of them can fly.

Where can I get one of those for Christmas? And PM the answer to the wife. Thanks.

But, the point is that as soon as the conveyor matches the car's speed, the car becomes stationary. At that point the conveyor stops moving, right?

Speed of object relative to distance traveled from a fixed point, not of the wheels turning. Two very different things and the source of all the confusion me thinks.
No matter how you formulate the question, it comes down to what is the conveyor belt's speed matching.

There you go DW. I think I killed it for good.

eurovol,

have you ever seen a car running on a dyno, i.e., a test bed having rollers on which the driven wheels of the car rest.

the driven wheels of the car drive the rollers around and around without the car moving. effectively, the circumferential surface of the rollers is equivalent to the hypothetical treadmill.

no matter how fast the wheels are driven, the rollers just rotate faster, without the car moving.

the point you are missing is that a plane is propelled by the jet engines, in this case. the wheels of the plane are not driven.

Worse try than the Dogs.

Oh Jimbo. You're such an old-fashioned boy.

Na-na-na-na-naa! I held out longer than you.

C'mon... we're sooooo close to post #1000 on this thread...

Been offline for a couple of hours. What's this about a car with a jetliner strapped to its roof?

The trolls are coming out of the woodwork now.

Meanwhile the percentage of people who think the plane will fly is going down...

Well, I didn't answer no.

Yeah right, you were all mistaken, have suddenly realised your errors and are too chicken to admit it! Yeah I called yer all chickens!

Ok let's have a new poll.

1) Sin and BD knew the correct answer all along and were trolling
2) Sin and BD have just realised what dopes they were and are trying to save face.

Owzat!

Chickens can't fly unless they are on a conveyor belt being powered by a jet engine. Aye, that would give them thrust!

That is not really MakeShitUp. If you were to try and hold the plane still, against the force of the jets - the premise that half of you were adhering to - then that is the only way it would work. The energy would have to go somewhere and the only place for it to go is into the angular momentup of the wheels in such a manner.

Not made up shit, but the only logical explanation to keep the plane still like the no-fly numpties want.

They were trolling.

A better poll would be who still thinks that the means of propulsion actually matters?

No Tom17. It isn't possible for the plane to fly.

They are obviously saving face.