Wind powered vehicle that goes downwind faster than the wind?

[cold one]

Originally Posted by yguy

If a sail imparts energy to the air, where does it get that energy?

From the ground/water/ice, obviously.

[humber]

Originally Posted by spork

My memory is lousy, but I doubt very much he made a prediction he could be held to. It's not what he does.

Goldfish use you as a benchmark.

Originally Posted by spork

I think he's been careful not to make an actual prediction with the tell-tale as well. He says "it can do anything".

I predict that I would better be able to select a device for accurately determining the speed of the wind than you ever would.

Originally Posted by spork

But I enjoy the fact that he knows they'd never use such a device on an aircraft, when probably every sailplane I've ever flown has a piece of yarn taped right in front of my eyes on the windscreen.

Sporky thinks he's the only boy in the whole wide world with a sailplane.

I spelled the problem out, step by step, but you still could not reach the correct conclusion. There is no point in trying this in a car, unless you have some reference for comparison. You plan to test the device in question, with that same device, and even then, consider only one aspect of what was put to you. Brilliant. This is nothing to do with physics, but your logical and analytical skills.

Streamers are not used where accuracy is required. I don't have a sailplane, but I am sure that your windscreen tell-tale is small and short, and of the type used in windtunnel testing to show the flow over a surface. Quite different. (But of course, if you put it there, then there is no telling what it may be.)

You have also ignored the effect of mass on a TT. Too much mass dominates the tell-tale's behavior, and that becomes a problem for those wanting to know the behavior of the air. See how that works, Chief?
The mass, and how it is distributed, will greatly influence the TT's dynamic performance; response time, stability, hysteresis etc.

Everyone can now see another reason why no one would bet with you. They would have to spend too much time teaching you the basics, and you would still insist you knew better.

[recursive prophet]

Originally Posted by yguy

Do they indeed?

And all these years I thought sailboat fuel was a joke. Silly me.

I wouldn't think so. The prop, then, acts just like any other prop.

Hmm. Looking forward to a continuation of this line of thought. SZ? Spork?

Originally Posted by cold one

From the ground/water/ice, obviously.

And how do ground and ice transfer that energy again?

[semper]

Originally Posted by Harold Bricer

Yes simper, your solution is the simple solution which is correct in the particular case of the component of boat velocity in the direction of the current (downstream) is the same as the current velocity. Then the velocity vectors will add up exactly as you indicated. In fact, for high school vector mathematics, your solution is correct. But if you would like to learn how to think and also have a general solution to the problem, which would hold in all possible cases, you need to consider that the velocity component of the boat in the downstream direction is determined by the force of the water acting on the hull and reaches the current velocity as a limit. The force acting on the hull is dependent on the area of the hull that the current is acting on. That area is quite different when the boat is going across the current or down the current. By examining the geometry of a typical speedboat, it is easy to see the force of the current is much greater when the boat is crossing the river instead of going up and down the river. This means that you cannot simply use Vwl as the top leg of your vector triangle, but must replace it with an mathematical expression based upon the cross sectional area of hull that is acted upon by the current. It makes the math much more complicated, and that is why almost all texts will use the simple solution that you have used. All I am trying to point is the fact that is not a general solution and with a very high boat velocity and a big difference between the beam length of the boat and the bow to stern length, there is a point where the transit time up and down is less than the transit time back and forth. Perhaps if you solve the problem of the work required to move the ball through the wind force field, I will find a particular solution where the up and down trip is faster than the cross river trip, but no promises! What I can do is offer the extreme case where the beam is so narrow and the boat is so long that all the full force of the current acts when the boat crosses the river and no force of current acts when the boat goes up and down. Then you can readily see the up and down trip is faster!

Oh I see! You are one of them. Anyway, I'm glad you liked my simplified solution. Now we just need to look at the actual simplification and idealisations, and try to reject (or verify) the imagined ones.

This could be difficult for me Harold, because as I was just walking along our East West direction corridor, I realised I'd forgotten my keys, so I quickly turned around on the spot to walk the other way. Well, you can imagine what happened... I'd completely forgotten that my "absolute" velocity would change in the order of 1000mph. I went for quite a tumble.

That same kind of imagined effect happens in aeroplanes and boats too I guess. There are numerous debates devoted to "Downwind Turning Myth" etc, I'm sure you heard of them. The informed posters here certainly have. It is good that you reaffirm this understanding.

[cold one]

Originally Posted by recursive prophet

And how do ground and ice transfer that energy again?

Through relative motion, like most other things. For any sailboat/cart of a fixed tack you can work in a frame where the energy comes from the air. You can also work in a frame where the energy comes from the ground/water/ice. Both are correct and equally valid. In any frame the total energy balances.

Think of two ships A and B colliding in space. In the frame where A is initially at rest, A gains velocity and therefore kinetic energy and B loses energy. In the frame where B is initially at rest, the opposite is true. Which transferred energy to the other?

There's no answer to that, it's like asking which has a larger velocity or which is farther from the y-axis.

[semper]

In fact Harold, the complete lack of understanding you bring to this subject is a wonder to behold.

If you were an aeroplane pilot (you can still get your licence even if you are a complete knumbnut on these matters), and you were flying a North South Track in an East West wind, you would think you'd have an aerodynamic side load wouldn't you?

You wouldn't understand that the relative airflow should still come inline with the longitudinal axis of the fuselage, so you would force the aircraft to fly with a high Beta angle, uncomfortable for your rudder peddle leg and rather bad for your fuel consumption, but at least you wouldn't have to understand the problem.

[ThinAirDesigns]

Originally Posted by ThinAirDesigns

yguy, the sails on sailboats, ice-boats, land-yachts -- ALL of them do EXACTLY that on a broad reach ... they act as propellers (accelerating the air relative to themselves, and moving air from the low pressure side to the high pressure side.)

Originally Posted by yguy

Speaking of preferred reference frames...

Dude, that fact is the *opposite* of "preferred frame" it's *totally* frame independent. Pick the frame ... any frame, and the stream of air leaving the turbine will be closer in speed to the turbine than the free stream of air entering the turbine -- that's how a turbine 'harvests' energy. The opposite is true of a prop and that again is *frame independent*.

If a sail imparts energy to the air, where does it get that energy?

Now that CAN depend on which frame you look at it from, but one way to look at it will result in the answer that Cold One has already pointed out -- from the *other* medium. The earth's rotation is actually *slowed* just a tiny bit and that's where the energy comes from.

Again, that depends on the frame ... let's look at it the frame of the earth for instance -- both the prop on the DDWFTTW cart and the sail on the broad reach are doing something that is very, Very, VERY counter-intuitive ... they are *both* accelerating the air AND slowing it down. Oh, you must be crazy you say (well, at least Harold will say that) but wait, don't run way:

The airfoils of both the cart and sailboat are accelerating the air *relative to themselves* AND slowing the air down *relative to the earth*. It's this capability that allows a prop to produce a 'net gain' in energy under the right conditions.

Let's use bowling balls as air molecules to help demonstrate a thought experiment:

There lies a straight and level road running parallel to the equator. 'Blowing' down the edge of this road from east to west (we'll say left to right in our view) is a row of bowling balls moving by at 10mph -- the bowling balls are spaced 10ft apart and happen to be floating 3ft above the road. As we sit in our redneck lawn chair on the other side of the road and watch, there is the endless stream of bowling balls blowing by ... whoosh ... whoosh ... whoosh...

Suddenly, we nearly jump out of our skin as this silent little cart with two little guys on it come whipping by at 15mph -- also moving from our left to our right ... whoooooosh ... gone. "WTF?" we think to ourselves. We have no more again leaned back again in our chair when we notice something very odd ... the tempo of the passing balls has changed. They've slowed waay down and are now passing at only 5mph ... whoosh ... ... ... whoosh ... ... ... whoosh ... ... ...

We realize that we've had a running video camera on our armrest the entire time so we quickly rewind until we have the silent little cart entering our view from the left. At his point we go to super-slow-mo and watch the action as the cart passes by. We watch as the guys on the cart as they reach forward, grab these balls and throw them rearward with all their might.

(I pause to remind you of our posted speeds :
Balls ahead of cart = 10mph
Cart speed = 15mph
Balls behind cart = 5mph)

As they do this, two things happen:

A: the speed of the balls relative to the cart goes up -- while they are approaching balls at 5mph, they are moving away from the balls behind them at 10mph.

B: the speed of the balls relative to the ground slows down by 5mph.

So, as you can see, the two guys on the cart (analogous to the prop blades) can *both* accelerate air (the hallmark of a prop after all) AND slow it down (which is necessary for there to be a net gain in the energy aboard the cart).

Now, it's really easy to say "hey, but the two guys are expending energy of their own -- yes they are, but replace those two guys with a linkage to the wheels and now you're free of the human intervention.

(and NO, the paragraph above doesn't work if the balls are stationary relative to the road ... THAT would be perpetual motion. The fact that the balls are moving relative to the road and we use a linkage to the road to slow them down relative to the road allows us the energy to move along the road as well)

JB

[ThinAirDesigns]

yguy, considering a couple of your responses it might be worth making a broad statement and asking you agree or disagree.

Here's my statement:

"All relative speeds between objects remain the same no matter which frame the objects are viewed from."

It appears to me that perhaps you would take issue with the above and it will pay to make sure we come to terms.

Thanks

JB

[humber]

Originally Posted by cold one

Through relative motion, like most other things. For any sailboat/cart of a fixed tack you can work in a frame where the energy comes from the air. You can also work in a frame where the energy comes from the ground/water/ice. Both are correct and equally valid. In any frame the total energy balances.
Think of two ships A and B colliding in space. In the frame where A is initially at rest, A gains velocity and therefore kinetic energy and B loses energy. In the frame where B is initially at rest, the opposite is true. Which transferred energy to the other?
There's no answer to that, it's like asking which has a larger velocity or which is farther from the y-axis.

The symmetry that you suggest is not there, cold_one. The energy "flows" to the frame where it is dissipated. To exaggerate, if one frame has a power station on it, and the other a city, you can hardly say that you could arbitrarily decide which was the source of the energy. It is no good saying that Icould from one frame, say that the energy were flowing the other way, because no matter what, I still have to put real coal in the burners.
Frames of reference is a very simple concept. Absolutely nothing changes because of it. It is a change of perspective, that is all.

The question of two colliding objects is always raised. It was put to me earlier in this thread, that if an astronaut propels himself by pushing on the ISS, then it cannot be said who is in motion. Of course you can. There are many ways. But one is very obvious. What if there were a second ISS, in the same orbit, but within 1m of the other? It would be difficult to explain why my pushing away from one ISS, resulted in the other also apparently moving away at the same speed.
This A hits B thing only works for 2 objects, and where there is no gravity, otherwise it is exposed for the narrow and artificial example that it is.
It is not possible to tell under those circumstances, because the entire Universe has been reduced to those two objects. What do you expect?

There may be no absolute space, but what possible effect can it have on you? The case is by no means closed BTW, and if the Universe turns out to be finite, then absolute space becomes meaningful. It makes no practical difference to anything on this planet.

[Subduction Zone]

Originally Posted by ThinAirDesigns

yguy, considering a couple of your responses it might be worth making a broad statement and asking you agree or disagree.

Here's my statement:

"All relative speeds between objects remain the same no matter which frame the objects are viewed from."

It appears to me that perhaps you would take issue with the above and it will pay to make sure we come to terms.

Thanks

JB

Of course not, but I don't think this is the place for a debate on SR

[Subduction Zone]

I see by humber's latest post that he still believes in a flat Earth that is at the center of the universe

[cold one]

Originally Posted by humber

The symmetry that you suggest is not there, cold_one. The energy "flows" to the frame where it is dissipated.

Energy doesn't "flow to frames", that's trollish trollspeak. Pick a frame and stick to it, then you can see what the energy does. But you'll get different answers if you pick a different frame.

if one frame has a power station on it, and the other a city,

It's that kind of comment that convinces me you're a troll. I'm sure you don't think "frame" means "picture frame" or something, I bet you understand what it means and why that sentence is pure concentrated stupid. You just say that shit to astonish everyone with your amazing ignorance and provoke a response. But apart from this, I'm not falling for it.

[humber]

Originally Posted by Subduction Zone

I see by humber's latest post that he still believes in a flat Earth that is at the center of the universe

I don't think this thread should wander to GR, but the concepts are being mixed.
OK Space Cadet SZ. I posted a passage from Bertrand Russell. What do you think he means by this;

"A certain type of superior person is fond of asserting that 'everything is relative'. This is, of course, nonsense, because, if everything were relative, there would be nothing for it to be relative to."

[Subduction Zone]

Originally Posted by humber

I don't think this thread should wander to GR, but the concepts are being mixed.
OK Space Cadet SZ. I posted a passage from Bertrand Russell. What do you think he means by this;

"A certain type of superior person is fond of asserting that 'everything is relative'. This is, of course, nonsense, because, if everything were relative, there would be nothing for it to be relative to."

Bertrand Russell was pointing out in the world of moral interactions not everything is relative. He was not talking about physics, that was not his specialty. Talk about quoting something out of context

[humber]

Originally Posted by cold one

Energy doesn't "flow to frames", that's trollish trollspeak. Pick a frame and stick to it, then you can see what the energy does. But you'll get different answers if you pick a different frame.

That troll talk is a prophylactic defense. If I could fool you, then your knowledge is unsound. If it's unsound, how can you be sure you are right?

Energy certainly does have a source and destination. Is The Carnot cycle not familiar to you? But there is no reason to invoke that, because your claim is in defiance of all observation.
You can see what the energy does from any frame, yes, but that does not allow the arbitrary assignment of the source of that energy. You are mixing ideas, and forsaking other scientific precepts such as laws of thermodynamics, in favour of a view based entirely on relative motion. The treadmill relies on misunderstanding to explain its operation, and to explain away its errors; that is the only real connection the treadmill has with frames of reference.

if one frame has a power station on it, and the other a city,

It's that kind of comment that convinces me you're a troll. I'm sure you don't think "frame" means "picture frame" or something, I bet you understand what it means and why that sentence is pure concentrated stupid. You just say that shit to astonish everyone with your amazing ignorance and provoke a response. But apart from this, I'm not falling for it.[/quote]

Picture frames? Of course not, frames of reference are just relational; it's in the name.
I used the the power station (and I did say it was an exaggeration), because I thought it was illustrative. For our purposes, it could be an object's KE, or the KE of the wind. The same rule applies. There is are definite sources and destinations.

[humber]

Originally Posted by Subduction Zone

Bertrand Russell was pointing out in the world of moral interactions not everything is relative. He was not talking about physics, that was not his specialty. Talk about quoting something out of context

Oh Good Grief SZ. The quote is from the ABC of Relativity. He was also a mathematician, and with Whitehead, wrote the Principia Mathematica.

Now that is out of the way, what do you think he means? It's not philosophy but logic. If you don't see the paradox, (other than the words) then you don't understand the problem, nor GR.

[Martin.au]

Originally Posted by ThinAirDesigns

Alright folks, spork and I are getting ready to do another "test" and post a video of the results. I'm asking for people to post there predictions:

We will tie a streamer (crepe paper, whatever) to the antenna of my car and drive it in a large parking lot or side street in still air (likely early tomorrow morning. We will drive @ ~30mph and then immediately slam on the brakes with the force necessary to lock said brakes and slide the car to a stop violently.

Will the streamer point to the front of the car during this extreme braking manuever, or will the streamer still be pointing at the rear of the car and still indicating relative wind direction?

(We will likely also include a sock with a rock in it hung along side as well, just so humber can feel good about himself.)

JB

That's actually pretty tricky because your car antenna is going to go mental when you hit the brakes (like when hitting a bump). It will throw the tell tale all over the place. Don't forget, the car antenna is a big spring.

[Subduction Zone]

Bertrand Russell was first off a philosopher. That was not a physics statement he was making, he may have been a lot of things but physicist was definitely not one of them. He was talking once again about moral relativity. And even if he was talking about his disbelief in physics it is meaningless. If I described to spork how a large exposure of metamorphic rock can represent a pressure temperature phase diagram and he disparaged my claim it would not have very much weight at all, it is something totally outside his expertise. If Russell was describing physics it is meaningless, it is totally outside his specialty of philosophy and mathematics.

[semper]

We have yet to find anything within Humber and Harold's field of expertise.

[ThinAirDesigns]

Originally Posted by Martin.au

That's actually pretty tricky because your car antenna is going to go mental when you hit the brakes (like when hitting a bump). It will throw the tell tale all over the place. Don't forget, the car antenna is a big spring.

Martin, the antenna on my car (Prius) is a rather short stub only about 12 or so inches long on top of the car. It it's too flexible, I'll stiffen it up with a stick and a bit of tape.

JB

[humber]

Originally Posted by Subduction Zone

Bertrand Russell was first off a philosopher. That was not a physics statement he was making, he may have been a lot of things but physicist was definitely not one of them.

He was a mathematician, and one good enough to keep company with Hilbert, Godel and Einstein, to name but a few. On the philosophy side he tutored Wittgenstein. Is that enough authority for you, or is it only sports-jocks that do it for you?

Originally Posted by Subduction Zone

He was talking once again about moral relativity. And even if he was talking about his disbelief in physics it is meaningless.

So he is definitely taking about moral relativity, but if he's not then...
Where is you logic, SZ?

Originally Posted by Subduction Zone

If I described to spork how a large exposure of metamorphic rock can represent a pressure temperature phase diagram and he disparaged my claim it would not have very much weight at all, it is something totally outside his expertise. If Russell was describing physics it is meaningless, it is totally outside his specialty of philosophy and mathematics.

I have the book, I can send you a pdf. PM me.

"A certain type of superior person is fond of asserting that 'everything is relative'.This is, of course, nonsense, because,if everything were relative, there would be nothing for it to be relative to."

Now, what do you think he means? Not the superior bit, that's just sarcasm,
the underlined., and particularly the emboldened.

[Martin.au]

That might work then.

[humber]

Originally Posted by semper

We have yet to find anything within Humber and Harold's field of expertise.

Now,now, Semper. Do you recall that I did say that I thought your questions were over-simplified? Your examples are not so much physics, but mathematics. As I think Harold is saying, you've left out all the bits that make it a problem.
Like considering the different effects that the river will have according to direction. It's just a numbers game, one of vectors. Fine as it is, but it says nothing about the physical world.
It seems to me, and illustrated by your corridor example, that you do take this "vector like" view. It's the same with the treadmill. Perhaps it adds up numerically from a vectorial point of view, but like the boat example, everything else has been left out. That's why simple physical questions, bring it to its knees.

[Martin.au]

Funny. I thought you were the one who seemed to have issues with the physical world, humber.

Everyone else here has observed that it's possible (iceboats, treadmill, etc) and are now looking for ways to explain it, such as the math. You, however, seem to rely on your intuition, some very dodgy hunches and a complete lack of interest in testing it yourself in an attempt to dismiss the physical world.

[humber]

Originally Posted by ThinAirDesigns

Martin, the antenna on my car (Prius) is a rather short stub only about 12 or so inches long on top of the car. It it's too flexible, I'll stiffen it up with a stick and a bit of tape.

JB

Sticky tape? While you are there, don't forget to monitor the wind and car speeds, so that you can accurately report your results. After all, the treadmill only shows about 0,1m/s over windspeed, and to be sure at that resolution, you are go to need some really good gear.

Do you think slamming on the breaks may have more to do with the mass of the TT than anything else? That's really quite obtuse of you. In order to refute my point, you are going out of your way to prove it for me. How do you get by in the world?