From Modern Mechanix:
Yes, these things are exactly what they look like. And when the design was tested, no, it didn't work. You can't power an aeroplane with a sail.
"Common sense", whatever that is, says it's impossible to make a sail-powered aeroplane. And common sense is right.
But if your vehicle has a connection of some sort to the ground, or water, it is eminently possible to sail faster than the wind. Tacking sailing ships do this routinely. Common sense doesn't say that's impossible, unless it's the common sense of someone who's never seen a boat race.
But common sense most definitely says that sailing dead downwind, with the wind exactly at your back, cannot be done faster than that wind is blowing. Obviously, whether you're in a boat or in a land yacht (meaning a wheeled vehicle propelled by the wind, not a '71 Impala), when your speed and heading relative to the ground or water are the same as the wind speed and heading relative to the ground or water, there's no more energy to be harvested and you can't go any faster.
In this, common sense is absolutely wrong. A land yacht certainly can sail downwind faster than the wind.
The fastest one to do so thus far is called Blackbird, but there are others:
What all of these yachts have in common is a large propeller instead of a sail, and the prop has a drive connection to the wheels. Common sense says this won't make a blind bit of difference to anything, but it does.
There have been some rather nasty arguments between people who know that this cannot be done and people who, as per the old saying, should not be interrupted because they're busy doing it. Enjoy the comments here, for instance, if you'd like to consume rather more than the recommended daily intake of flame-war.
At this stage, anyone who still objects is in the position of a person in 1910 who still insists that aeroplanes are impossible on the grounds that he, personally, hasn't yet seen one flying.
(Although, to be fair, some of the land-yacht runs are alleged to have been made on the dry bed of Ivanpah Lake. I've been there in Fallout: New Vegas and it's clearly not nearly big enough for any such activities.)
Common sense is, in general, immensely useful. It's what tells you that, when you want to cross the street and see a car coming, you shouldn't just step out in front of the car, even if you've never subjected this belief to empirical testing by walking out and seeing what happens.
But common sense, like memory and even perception itself, is unreliable. Common sense only works on things that it's worked on before, and the only way to expand your common sense to deal with new concepts is by making those new concepts fit into some part of the existing framework. Expanding your common-sense framework to accept genuinely new ideas is possible, but it doesn't happen automatically.
If you're trying to figure out whether to step out in front of a type of oncoming car you've never seen before, the common-sense shortcut will work. But if you're trying to understand some new, counter-intuitive physical oddity like these land yachts, common sense will fail you miserably, just as it so often does when people try to think about tax brackets or daylight saving, and on the rather fewer occasions when people try to think about aeroplanes on conveyor belts.
I don't think all of the people who got into shouting matches over the downwind-faster-than-the-wind idea were just emotionally invested in a position they'd not thought about at all, as is so often the case in, say, political arguments. The physics involved is decidedly non-obvious; that, plus Sayre's Law, could account for the whole kerfuffle. And this new development doesn't seem likely to revolutionise land transportation, or anything else.
The next time you're inclined to take a common-sense view of some new idea that actually matters, though, try to bear in mind that common sense also says that the world is flat and the sun goes around it.
4 May 2011 at 8:58 pm
Common sense! That's where I'm a viking!
(Whenever I think I have explained a concept completely unambiguously, I contemplate situations such as that, and I go over the text a few more times.)
4 May 2011 at 9:05 pm
(That is to say, the very content of common sense can vary wildly. It's common knowledge in some parts of the world that running an electric fan at night will kill you by asphyxia, no doubt because of some mental heuristic involving carbon monoxide poisoning and liquid fuelled motors.)
4 May 2011 at 9:15 pm
Oh, yeah - that astonishing Viking flamewar is now one of my own go-to examples of nothing really being "obvious", too.
(I've never actually had a person tell me face-to-face that they don't take the straight, Ralph-dreams-he-is-a-Norseman, interpretation. I'm too scared to ask people very often, though. I may in fact be surrounded by people who believe everything said by a small child must be a deep and poetic metaphor.)
5 May 2011 at 10:09 am
That squealing clanking noise you just heard was my brain breaking.
5 May 2011 at 10:14 am
The only way I can this working in my head is to see the spinning prop blades as each essentially working the same way as a conventional sail moving at an angle to the wind.
5 May 2011 at 5:52 pm
That downwind-faster-than-the-wind conundrum is something I spent a couple of sleepless hours on a couple of months ago. It's definitely counter-intuitive, but I found that this quote:
that I found in a comment on this blog, was quite helpful.
(By the way, anyone with any interest in energy ought to read the book by the author of that blog: Sustainable Energy without the hot air - It's something as rare as a serious analysis of various energy supply schemes, by a real bona fide physicist who knows what he's talking about. Highly recommended!)
5 May 2011 at 6:52 pm
Here is a good video illustrating the principle: http://www.youtube.com/watch?v=k-trDF8Yldc
5 May 2011 at 9:27 pm
You can sail a yacht (Big blue wobbly thing that mermaids live in - type) downwind quicker than the wind.
Like the land yacht, it all depends on how you define 'downwind' - any good high-performance racing yacht will be able to tack on a downwind reach at velocities higher than the true wind speed, allowing them to reach a downwind mark quicker than the wind speed.
Even low-performance yachts can do it for short periods by clever skippering - you can sail slightly off the wind to one side, while steering the boat slightly in the opposite direction. The sail is not true downwind, it is slightly reaching and generating a lift vector off the true wind direction, but the keel and rudder (in short-hull-length skiffs and dingies at least) combine to create a hydrofoil creating lift on the other side of the centreline. The addition of the vectors gives you a total higher than true wind speed, in the same direction as the wind. It is bloody hard to do though, as you have to exactly balance the sail and keel forces or you will be going for a swim - the boat is very dynamically unstable in this configuration, and is at high risk of a nasty event called 'Dutch Roll'. In aircraft, this will make you ill. In sailing, this will snap the mast off and pitch-pole you (pitch the boat forward over the bow, usually catastrophically).
However in small dingies, where the human crew can move quickly enough to damp oscillations, and be intuitive enough (sometimes) to pre-emptively damp oscillations (using the spice melange helps...) and you can sail in this manner for long enough to overtake other boats in the same wind. It is even better if you have time to see the boggled expression on their faces as you slowly move past while clearly being beside them - usually you have to overtake by 'stealing' their wind - putting your wind shadow over them.
None of this takes into account the more complex dynamics you can use when you encounter cross-currents, or use the hydrodynamic lift from the hull to maneuver the boat, or use dynamic ballast systems, or canting keels, or rigid sails, or any of the other systems yachts use to go very fast for free (once you've paid for the boat - something that never ends...).
And yes @Popup - "anywhere there is relative motion there is energy to be had" - thats exactly what the above technique does.
It's not as 'pure' downwind as the land yacht, but common sense says that shouldn't matter :-)
6 May 2011 at 2:40 am
Ow.
Alright, let me think this though. They've got a generator hooked up to the wheels, which powers a propeller. This would usually be a perpetual motion machine, but they're getting energy from the wind at their back, which means they can get away with sub 100% efficiencies.
And, yes, they are moving faster than the wind, but the force still exists, in a "I have to do less work than if there was no wind" kind of way.
That about right?
6 May 2011 at 11:57 am
I nearly turned my head inside out trying to figure this one out on my own.
I was pretty skeptical until I saw this vid: http://www.youtube.com/watch?v=FqJOVHHf6mQ&feature=related.
Apparently it's all in the angle of the prop blades; tilt them more aggressively and it will move into the wind.
I am torn between feeling that my understanding of the world has been rudely violated and humbled by the cleverness of others.
7 May 2011 at 12:12 pm
>> "to be fair, some of the land-yacht runs are alleged to have been made on the dry bed of Ivanpah Lake. I’ve been there in Fallout: New Vegas and it’s clearly not nearly big enough for any such activities."
Your common sense is failing you once again. I'll be happy to post videos of myself piloting the Blackbird to better than 2X wind speed on the dry lake in Ivanpah. We did this during the NALSA America's Cup event last year.
On another note, I see that several of the folks here seem to have a good handle on how this works.
7 May 2011 at 1:03 pm
Your common sense is failing you once again.
Uh - the joke is that everything in Fallout: New Vegas is tiny and squished together (because otherwise it'd be a five-day hike in monster-infested desert to get from anywhere to anywhere else). In the game, you can walk from Primm to Nelson in about five minutes :-).
We did this during the NALSA America's Cup event last year.
Awesome!
7 May 2011 at 1:45 pm
Okay, I'll admit, I've only had a year and a half of physics classes, but that covers most of the major Newtonian bases such as would generally be relevant to a significantly macroscopic object like a vehicle, and for the life of me I cannot think of any reason why any reasonably intelligent person would think it should be physically impossible to make a wind-propelled vehicle go faster than the wind.
It's going to require some actual *engineering*, sure. You can't just hold up a piece of sailcloth and expect it to propel you at twice the speed of wind (in much the same way as you can't just throw any random hunk of steel in the water and expect it to float, unless you shape it in a manner such that it displaces more than its own mass of water). But why on earth wouldn't it be possible? It should be possible, with the right design. I am not aware of any model in physics, even an oversimplified one, that would suggest otherwise.
Fundamentally, if the wind can propel an ultra-lightweight object (like a leaf, say) at a given speed but can also propel a significantly denser but equally simple object (like a sheet of aluminum) at very nearly the same speed, then obviously it can exert more force than is required to propel the leaf at the speed in question. Why does the leaf not go faster then? Because it's just a simple sail-type object. An ultra-lightweight object designed to harness that extra force and *do* something with it should be able to go faster. It's just a question of figuring out how to harness more of the wind's force than a stupidly-simple design like a leaf or kite can do.
There will be practical limits to how much of a multiplication you can manage, sure, but those will be due to mundane reasons like the tensile strength of your building materials, the quality of your lubricant, and so on.
I'm not entirely sure I understand how the propeller-geared-to-turn-the-wheels design would work, since if the vehicle tries to accelerate past the wind speed the propellers ought to be changing their direction of rotation, unless I'm missing something. But that's a design issue, and you can get around design-specific issues like that by introducing a better design.
It's not at all the same as theoretical impossibility (like, say, trying to move an object with a positive real rest mass faster than the speed of light, or extracting unlimited free energy from the cosmic aura of the generator's own atoms, or conditioning water molecules to remember toxins to which they've been exposed and exert the opposite effect on living systems).
*Shrug*. Maybe I just don't have enough common sense to understand why it won't work. Too many math classes will do that to you, I guess.
7 May 2011 at 2:34 pm
>> " I cannot think of any reason why any reasonably intelligent person would think it should be physically impossible to make a wind-propelled vehicle go faster than the wind"
While I'm inclined to agree with you, I can still give you a list of professors (Aero, M.E. and physics) that assured me it would not be possible. Some of them still maintain that position - despite the real world evidence - and the fact that I posted detailed build videos so anyone can easily make their own small scale working model and prove it to themselves.
>> "I'm not entirely sure I understand how the propeller-geared-to-turn-the-wheels design would work..."
The propeller does not turn the wheels. The wheels turn the propeller - at all speeds from a stand-still to wind speed, to 3X wind speed.
>> "if the vehicle tries to accelerate past the wind speed the propellers ought to be changing their direction of rotation"
No need for the propeller to change pitch or direction. We ran it at Ivanpah with a fixed pitch prop and fixed gearing. The gearing remains fixed, but we added a variable pitch prop to improve the low speed acceleration (which is still awful). But the acceleration at around 30 mph is faster than our chase vehicle.
>> "Maybe I just don't have enough common sense to understand why it won't work"
That's a good quality to maintain. The greatest impediment to learning anything is already knowing everything.
8 May 2011 at 7:10 am
"Common sense is the collection of prejudices acquired by age eighteen."
-- Albert Einstein
9 May 2011 at 1:17 am
>> "the joke is that everything in Fallout: New Vegas is tiny and squished together"
D'OH! It wasn't your common sense failing you, but my reading comprehension and sense of humor failing me!
I was wondering how Richad Jenkins could get the Greenbird up to 126 mph on that dry lake, and you doubted our meager task.
9 May 2011 at 1:47 pm
I'm thinking in terms of 3-4-5 triangles...
You have a side-wind of 30 knots (90 degrees from forward). You are travelling forward at 40 knots, ie. faster than the wind.
Someone standing on the deck would measure a wind speed of 50 knots, at an angle of 53 degrees from side, or 37 degrees from forward.
From their point of reference, they are doing 40 knots in a 50 knot wind (ie. slower than the wind)
9 May 2011 at 3:39 pm
>> "From their point of reference, they are doing 40 knots in a 50 knot wind (ie. slower than the wind)"
True. But this cart can go directly downwind faster than the wind. In a 10 knot wind, it can go directly downwind at 10 knots, 11 knots, 20 knots, etc. It set the record at 28 mph directly downwind in a 10 mph wind.
Also, there are sailboats that can tack downwind faster than the wind. In other words, they can get to a point directly downwind faster than a balloon drifting with the wind. And they do not have to have a relative wind greater than their speed over the water as in your example.
9 May 2011 at 8:45 pm
My common sense is weird. I'm thinking that a land vehicle with nearly frictionless bearings on the wheels can go faster than a vehicle on water. The boat has more friction than the land vehicle.
Given the same sails or whatever means of propulsion, I would think that the land vehicle is the faster one.
10 May 2011 at 12:28 am
I would generally agree that it's more challenging to go really fast on water for a number of reasons. Greater drag is the prime culprit, but the uneven and dynamic surface is a huge challenge, as are the issues of cavitating and venting.
10 May 2011 at 1:52 am
As a skeptic, I'm fascinated by the effect this is having on my brain.
If I'd just met you, spork, and you made this claim about your LAN yacht, I doubt I'd believe you. I wouldn't dismiss you outright; a good skeptic shouldn't, and I'm mostly ignorant about wind power, and I've heard of tacking. But I don't fully understand tacking, either, and this sounds even more counter-intuitive than tacking.
But I DO think this is very probably true. Why am I ignoring my common sense? Because Dan told me about it. I trust Dan. He tells me interesting things about weird stuff and backs it up with evidence. But that's still shaky logical ground! If anyone else told me they believed something because some unknown Australian on the Internet with a cat-photo fetish told them it was so, I'd be less confident in their claim. Much as I trust Dan, there still isn't anything fundamental to "Dan said it" that makes it true.
"Trust but verify" seems the order of the day. So now I have to get off my lazy rear to figure out how to modify my common-sense framework. Thanks a LOT, Dan...
10 May 2011 at 1:56 am
Of course, LAN yachts sound almost as fun as funky-propeller land yachts...
10 May 2011 at 5:12 am
jaranth,
Skepticism is a good thing. Blanket denial without careful consideration is not in my opinion. Sounds like you're open to understanding this thing. Interestingly, there are a number of ways to approach it, and I'm happy to describe it to your satisfaction if you like.
10 May 2011 at 1:58 pm
Thanks, spork. I don't mean to seem pedantic or artificial; I was just struck by the psychology of how I responded to this. I think I understand the "woo" mindset a little better now. I might pick your brain, but I oughta try working it out from the available material (which I haven't yet) before bothering you.
10 May 2011 at 5:09 pm
Just as I got comfortable with tacking and 3-4-5 triangles, you up the ante with direct downwind. Oooh my aching head!
Only example that comes to mind is - a toy car with a flywheel. Thanks to the gearing, they are harder to get started but they go longer.
If the force is from a sail / propeller and the flywheel is the actual wheel, would that work?
If the vehicle goes TOO fast then I predict a back-force on the propeller, slowing it down and returning the system to some sort of equilibrium.
I'm afraid my mind won't expand past this point without medical assistance.
Bill Oddie, pass me the lemon sherbet.
11 May 2011 at 1:31 am
>> "I oughta try working it out from the available material (which I haven't yet) before bothering you"
Very good, but I should warn you... there is a whole lot of very wrong available material out there - much of it claiming to explain how the cart really works.
11 May 2011 at 1:37 am
>> "Only example that comes to mind is - a toy car with a flywheel. Thanks to the gearing, they are harder to get started but they go longer."
I understand what you're talking about, but I don't think that relates to the downwind cart. The downwind cart never relies on stored energy or momentum to go faster than the wind. Also, it will go faster than the wind steadily and indefinitely as long as the wind blows.
>> "If the force is from a sail / propeller and the flywheel is the actual wheel, would that work?"
There's really no flywheel to speak of. Clearly any spinning body will have momentum and inertial energy, but it can only give up that energy by slowing down. In the case of our cart, if the prop or wheels slow down, the cart must slow down as well. This doesn't happen as long as the wind continues steadily.
>> "If the vehicle goes TOO fast then I predict a back-force on the propeller, slowing it down and returning the system to some sort of equilibrium"
Yes. Let's say the wind was blowing 15 mph and the cart is going 30 mph. Then the wind backs off to 5 mph. In this case there would be a retarding force on the prop, and the cart would slow down to some multiple of the new 5 mph wind speed.
12 May 2011 at 2:04 am
I think the difficulty people have understanding this is that it's a complex dynamic system, with two modes of energy extraction going on.
Mode 1 involves considering the wind as just blowing on a static propeller and pushing it along; mode 1 energy extraction obviously can't go faster than the wind.
Mode 2 is more complex; the wheels turning the propeller cause it to "blow" against the wind. The maximum speed of the vehicle, assuming no losses or friction, is now the wind speed created by the propeller plus the wind speed blowing against the propeller, limited by the energy extracted from the wind. In practice, the various losses in the system mean you can't reach this.
The part that trips people up is that it's easy to build a device where either mode 2 energy extraction doesn't amount to enough energy to be the sole mode of energy extraction for the device at a constant speed below the point where mode 1 can't accelerate you further, or where the losses I skimmed over when describing mode 2 exceed the energy extracted by mode 2.
12 May 2011 at 4:41 pm
There's no question that it can be very counter-intuitive. That was my purpose when I first posed it as a brain-teaser. Even so, I've offered a whole pile of simpler examples to illustrate the principle. Sometimes these explanations help - sometimes not.
On another note, there is a very strong intuitive reaction for many people to conclude that there is some sort of an "air cushion" being developed between the tailwind and prop-wash. But this is not the case. The prop is simply propelling itself through a mass of air that happens to be moving (much like an airplane that happens to be flying down wind). There is absolutely no difference in the flow around an aircraft that's flying upwind vs. downwind. The same is true for the flow around our cart (and through our prop).
I hope this makes sense.
13 May 2011 at 4:16 am
Let me see if my own common sense or lack thereof will help me understand this...
Looking at the basics of wind energy, wind is a moving mass of air. Mass in motion has kinetic energy, so wind energy is really the kinetic energy of air mass times air velocity squared. Any object that makes the air slow down, that brakes the wind, is making the air mass give up some or all of its kinetic energy. That energy cannot simply vanish, it has to go somewhere. It goes into the object- a sail, for instance- that "caught the wind" and slowed the moving air mass down. Everything that runs on wind energy, be it a sailboat or a windmill, is extracting energy from the wind by slowing some of the wind down.
Now the propeller, here, is pushing back against the tailwind. It's trying to _slow the wind down_. In simple terms, propellers act on the whole cylindrical coloumn of air covered by the propeller's diameter. The propeller, pushing backwards against the wind, is slowing the wind down relative to the ground in that rather large-diameter coloumn. That's quite a lot of air-mass in motion, being made to slow down and thus give up some of its kinetic energy. We see, then, that energy must be extracted from the wind in exactly the same way as by a sailboat; by braking the wind and thus making it transfer kinetic energy to the vehicle.
The trapped energy acts upon the propeller circle and enters the vehicle via the propeller hub, acting upon the vehicle as a system. The energy thus caught gets geared up by the wheels and transmission, and is output in making the propeller spin faster. The propeller drives the vehicle forward relative to the air, and the faster it goes the more wind air-mass-in-motion gets slowed down relative to the ground so more energy is extracted from the wind etc until you run out of either wind or dry lakebed (or until you loose efficiency by having a propeller tip exceed mach 1 or something).
The only reason why this seems counter-intuitive is that we're not used to thinking of sails as having gear ratios, or of the ground forming part of a transmission system. The ground here acts much like a static ring wheel in a planetary transmission, only flattened out into a "ring wheel" of pseudo-infinite diameter. Wheel slip against the ground would rob the system of efficiency.
For a somewhat crude analogy, look at a common yo-yo with its string. Use a good, old simple one with a fixed axle, not a tricksy model with bearings. Ever tried to wind string onto the yo-yo by rolling the yo-yo on the floor, propelled by pulling on the string? Try doing that, while paying attention. As long as it rolls rather than slides on the floor, the string pulls the yo-yo _as a system_ forward relative to the floor, so the yo-yo rools on the floor. In rolling, it also spools the string up on its axle and winches itself forward relative to the string as well. This simple toy rolls forward _faster_ than the string pulling it, rolling against floor and string at different rates and moving forward at the sum of string-relative and ground-relative velocity. It's all about transmission ratios. Now call the string "wind", the axle "propeller" and the rim of the yo-yo "wheels". The differences in diameter between the axle and the rim is the transmission.
13 May 2011 at 9:18 am
>> "Now the propeller, here, is pushing back against the tailwind"
It's a mistake to say that the propeller is "pushing back against the tailwind". It is creating lift in the airmass in which it operates, and the result is that it produces a horizontal column of air that has been slowed relative to the ground. It's true that this shows us where the energy comes from (at least in the ground frame).
The secret is not that the wind and propeller are somehow pushing against one another - creating a sort of air cushion; but rather that the propeller is acting in one medium (the air) that's moving relative to the medium on which the cart's wheels act (the ground). By acting on the air (which is moving), the propeller does not have to use as much power to produce the same force (power = force x velocity).
>> "The energy thus caught gets geared up by the wheels and transmission, and is output in making the propeller spin faster..."
In the ground frame it's more accurate to look at the wheels and transmission as simply the kinematic constraint that causes the prop blade to follow a specific path - as the keel of a sailboat does for the sail.
17 May 2011 at 5:11 am
Spork,
You sir have made my decade. Back when I was wee lad (ok, 15 - which is too many years ago) I made a very similar prop to wheel driven small scale wind cart. While I never ran it on a treadmill to do any actual testing I did run it on my high school blacktop (300 yards of smooth asphalt) quite often and even occasionally had an anemometer available. On those occasions my measured speed of the cart was usually 5-10% above the measured wind speed. I was always puzzled by that but did not have the patience at that age to go through the physics of it and so just chalked it up to poor measurements! Turns out my measurements we're probably fine, it was my "common sense" that was off!
17 May 2011 at 12:10 pm
That is really cool to hear. I wish you had pics of the cart. I'd love to see it.
17 May 2011 at 1:58 pm
Um, I think you all are missing something. Motion is RELATIVE. Seriously it really is. This means that if the wind is at 15 mph and the cart is traveling at 15 mph then THERE IS NO WIND RELATIVE TO THE CART. And if the cart is moving 5 mph faster than the wind, this is just as mysterious as if the cart was able to move at 5mph WITH NO WIND! How is this possible? Once you've eliminated the impossible, whatever explanation is left, no matter how improbable, must be true.
In this case the one possibility that's left is HIDDEN in PLAIN SITE. Come on guys, don't make me say it. Somebody else step up to the plate and fill in the blanks here. :)
17 May 2011 at 7:03 pm
>> "Come on guys, don't make me say it. Somebody else step up to the plate and fill in the blanks here."
I give up. Time travel?
18 May 2011 at 3:42 am
Okay, here's another clue:
Why do so many physicists insist that what you are doing is impossible in spite of the evidence to the contrary? When you figure out what's wrong with their belief system, you will truly understand what you have accomplished here.
18 May 2011 at 4:15 am
>> "Why do so many physicists insist that what you are doing is impossible in spite of the evidence to the contrary?"
Because too many people learn in school, develop some simple ideas like "over-unity is impossible", and then go into teach mode. Once they're in teach mode they too often let their intuition guide them. And for too many, it's impossible for them to admit they were wrong - even after they see it demonstrated before their eyes.
18 May 2011 at 4:19 am
What is Denialism
http://scienceblogs.com/denialism/about.php
18 May 2011 at 4:27 am
Physicists don't insist that this is impossible. People who have quit employing scientific rigor to their observations and thought processes are no longer physicists. They may be teachers, professors even... but they are no longer physicists.
Also... jswendell... I sincerely hope you were going for the point Spork made and not some "physics is all wrong and I've figured out why!" Cause if thats where you were headed... well, lets just cut it short and say No, it isn't and no you haven't! ;)
Spork - I've got an old box of photos (yeah, actual paper photos from before the digital age) that I believe may have a shot or two of the Spanker (the cart in questions name - extra points if you know what the name refers to and no, it's not spanking). I'll take a look and see if I can't dig one up and post it!
Also, completely unrelated - Thanks Dan! Account all better now!
18 May 2011 at 5:13 am
"'over-unity is impossible'"
Okay, those where the words I was looking for. I guess you know then that it's not the wind that is powering your cart.
18 May 2011 at 6:34 am
>> "I guess you know then that it's not the wind that is powering your cart"
Actually, it is the wind that's powering our cart. But it's not quite that simple. Energy, like velocity, is frame dependent. So I can do the analysis in the wind frame and conclude that the ground moving beneath the wheels is powering the cart. It just depends on the reference frame you choose.
18 May 2011 at 7:45 am
jswendell.... over unity is in fact impossible in any frame of reference within our physical universe. This is not ambiguous science. This has been born out by theory and experiment and observation over and over and over and over. There has certainly been no lack of effort in attempting to achieve over unity but it just isn't possible. The laws of thermodynamics are both well understood (logically, experimentally and observationally)and not vague.
The Blackbird is NOT an over unity device. It is admittedly initially hard to wrap your head around how it works but it does indeed operate within the bounds of known physical and thermodynamic theory. The fact that some physicists and engineers refuse to believe the data and have yet to grasp the mechanics is unfortunate, but not surprising. It is a tricky concept indeed and even the educated fall prey to their preconceptions and "common sense" about how things work. The fact that these folks don't understand does not however mean that physics is all wrong and over unity is possible - it simply means that they don't understand. It says nothing at all about the state of current physics theory - in which basic thermodynamics and Newtonian mechanics have long been solved items.
Spork has made available many different forms of explanation attempting to make the counterintuitive nature of the Blackbird's performance easy to understand... in none of them does over unity play a role.
And to quote my favorite Australian musical comedic genius - "If perchance I have offended, think but this and all is mended! May as well go 10 minutes back in time for all the chance you'll change your mind!" (Tim Minchin)
18 May 2011 at 9:05 am
Okay I'll start over and try to be a little clearer. The first thing I said was "Motion is RELATIVE." It may seem strange, pointless, even asinine for me to be pointing that out, but I hope you'll bear with me. "Motion is relative" is a fundamental concept in physics, yet I see it being routinely ignored on a scale that is truly mind boggling.
If the wind is moving it 15 mph and the cart is moving at 30 mph, you could say the cart is moving 15 mph faster than the wind. But a more accurate statement would be, the cart is moving 15 mph relative to the AIR. Or just as accurately, the AIR is moving at 15 mph relative to the cart.
This is important to think about because if it was a windless day and you pushed the cart up to 15 mph, IT’S RELATIONSHIP WITH THE AIR WOULD BE IDENTICAL to the case where wind is at 15 and the cart is at 30.
Therefore, it is becomes clear that if you adjusted the gearing between the propeller and the wheels so that at 15 mph the propeller would turn just as fast as it presently does when the cart is doing 30, the cart would be propelled indefinitely.
This is of course impossible. This is why so many scientists, engineers physicists or whoever insist with utter certainty that this is fraudulent.
But if you change your gearing, and push that cart up to 15 mph, you’ll see that it will never stop. The power is not coming from the wind, it is coming from the air. This is what airfoils do. They reverse entropy. The airfoil IS Maxwell’s fabled demon.
Consider that if you actually corner a physicist and ask, “how do we know the second law of thermodynamics is absolute?”, they will have to admit that it has never been proven. It is accepted as truth because they claim, no one has ever observed an exception to this law. Well from my point of view, "because it hasn't been done yet", is a pretty feeble platform from which to declare a law absolute and unbreakable.
Furthmore the exception has been in PLANE site for over a hundred years now.
Consider a small single engine prop plane. If you rested it on a stand so it was pointed vertically, you could fire up that prop to it’s peak thrust and you would find it insufficient to lift the weight of the plane. That thrust represents 100% of the fuel supplied energy and it is insufficient to lift the plane. That’s why we use wings. Those giant airfoils are valving energy out of the air to lift the plane.
The insistence that the 2nd law is immutable is a form of mass insanity, just as building 400+ doomsday machines (nuke plants) and scattering them all over a highly seismically active planet is mass insanity. And finally, I’m sorry to say, imagining that your cart is being propelled by wind when you know that motion is relative, is a form of insanity. (I’m not disputing that wind starts the cart moving, but once it crosses the zero point, there can be no doubt that wind has nothing to do with it.)
We are all driven insane by socialization. We are so sure of the worldview that is presented to us by socialization that it never occurs to us to look in the most obvious of places for answers.
18 May 2011 at 12:19 pm
>> "The power is not coming from the wind, it is coming from the air."
Nope, the cart exploits the energy available at the ground/air interface. There must be relative motion between the two for the cart to operate. That relative motion (whether the ground moves under the air or the air moves over the ground) is wind.
The cart leaves a wake of slower moving wind when it passes. It's taken the energy out of that wind no differently than a sailboat does on a broad reach.
>> "Those giant airfoils are valving energy out of the air to lift the plane"
Nope. The wings are simply a much more efficient way to put that energy to use if you want to lift a plane. If you want the plane to hover, you just have to make its prop blades a whole lot longer and turn the prop more slowly. Then the prop will be the right tool for the job. It will kind of look like the blades of a helicopter (hmmm....), or like the wings of the plane. The engine has plenty of power either way - it's just a matter of using it efficiently. You can't climb a steep hill in your car in 5th gear, but you wouldn't claim 1st gear is extracting energy out of the universe.
>> "imagining that your cart is being propelled by wind when you know that motion is relative, is a form of insanity"
We call it education. To-MAY-to - to-MAH-to
>> "I’m not disputing that wind starts the cart moving, but once it crosses the zero point, there can be no doubt that wind has nothing to do with it."
And yet for some reason the cart stops when the wind stops.
18 May 2011 at 12:53 pm
I have no intention of engaging in a discussion about the laws of thermodynamics or the whole "science by committee" argument, but since jswendell is likely not unique in his views regarding the authenticity of the Blackbird I should point out the thing that most people seem to miss in this.
The prop at no time propels the wheels via it's turning. Actually the turning force the wind exerts tends to slow the vehicle down. The gearing of the prop to the wheels in conjunction with the angle of the prop blades ensures that the linear force of the wind on the surface of the prop is greater than the turning force exerted by the prop to slow the wheels. This is why the prop moves in "reverse". The trick is that when the craft is moving at any speed the angle of the prop blades is such that as the prop turns the blades present a surface that is still "travelling" into the wind - allowing the wind to exert a forward force on it - like a sail rather than like a windmill being driven around.
The the youtube vid I posted the link to above really does explain it very well. Just don't be hobbled by the preconception that the prop is, or should be, turning the wheels. It's a sail.
Unless I've completely got it wrong. Spork help me out here!
18 May 2011 at 1:05 pm
>> "since jswendell is likely not unique in his views regarding the authenticity of the Blackbird"
I think he considers it authentic; but he thinks it works for much more exciting reasons than you and I do.
>>
"The trick is that when the craft is moving at any speed the angle of the prop blades is such that as the prop turns the blades present a surface that is still "travelling" into the wind - allowing the wind to exert a forward force on it"
This is sort of true, but sort of tricky. The prop is working its way through a mass of air in exactly the way the prop on a Cessna does. There's nothing special about a tailwind "pushing" the prop from behind. From the prop's point of view, all the new air it encounters comes from in front - but not as quickly as it would if there were no wind relative to the ground.
>> "It's a sail."
Yes, the blades of the prop are identical to sails. But sometimes a sailboat sail acts as a propeller and sometimes it acts like a turbine. It depends on the course and speed of the boat. In the case of the downwind cart, the prop is a propeller - never a turbine. We are however building a turbine to make it go directly UP-wind faster than the wind.
18 May 2011 at 3:07 pm
> ‘The power is not coming from the wind, it is coming from the air.’
“Nope, the cart exploits the energy available at the ground/air interface. There must be relative motion between the two for the cart to operate. That relative motion (whether the ground moves under the air or the air moves over the ground) is wind.”
When the wind is at 15 mph and the cart is at 15 mph, the cart experiences NO WIND. Disconnect the propeller from the wheels and it would stop spinning, at least until the cart slowed down at which point there would be wind again. Beyond 15 mph the only wind that exists from the carts point of view is going in the opposite direction. So if you pushed or towed the cart past the 15 mph barrier while the rotor was disconnected from the wheels it would actually start to spin in the opposite direction.
So with the rotor connected, why does it continue past the 15mph point? Because the wheels are powering the rotor and the thrust generated by the rotor is adding more energy to the cart than the wheels are taking from it so it continues to accelerate. This is a dynamic that would be utter nonsense and impossible if new energy was not entering the system. Your rotor is an “over-unity” device. It is valving temp energy from the air. Why is this impossible for you to believe? I notice you made no response to my discussion of the second law.
>> ‘Those giant airfoils are valving energy out of the air to lift the plane’
“Nope. The wings are simply a much more efficient way to put that energy to use if you want to lift a plane. “
The rotor has a maximum amount of thrust it can generate. That maximum thrust is insufficient to accelerate the mass of the plane upward continuously at 32ft/sec^2. Seriously, think about that. For a plane in level flight it’s total mass must be continuously accelerated upward at 32ft/sec^2. That takes energy. The only energy coming from fuel, through the prop, is undeniably of insufficient magnitude to accomplish that task. Where is the extra energy coming from? Don’t you see, that’s why I’m calling this mass insanity. It’s obvious, terribly obvious that the wings of a plane are introducing extra energy to the system and the only place they can get it is from the air.
>> ‘imagining that your cart is being propelled by wind when you know that motion is relative, is a form of insanity’
“We call it education. To-MAY-to - to-MAH-to”
I wasn’t trying to be insulting. I was discussing mass insanity and I didn’t mean it as a slight that I included you in that equation.
I’m one of these weird guys that I don’t care what other people think, I’m still going to look at a problem objectively using simple logical principles. And if logic provides an answer that contradicts what a million other people are saying, I’m okay with that because if I deny my own ability to reason, then I can truly know nothing about the world.
Here’s a question for you. Has it occurred to you, for even a moment to consider the possibility that my arguments have merit?
Really, did it ever cross your mind for even a moment? Is it presumptuous for me to believe, of course not?
I consider mass insanity to be taking other people’s word for it that such and such and so and so is the case even if it defies logical scrutiny, though most people I would include in this “mass” never make it to the scrutiny part.
Science has been overtaken by religion and the totally unproven yet universally accept 2nd law of thermodynamics is an excellent example of this. If you even hint that you think it can maybe be broken, people such as our friend Mr. Stark, can’t get in line fast enough to tell you that your nuts. We have a strong social incentive to disregard logic and accept religion in it’s place. To yield to that social incentive is insanity.
Here we have a situation where science is telling you clearly that what you have accomplished is impossible yet mysteriously you appear not to be questioning the established paradigms. Rather than consider the possibility that you’ve simply broken the rules, you would rather believe that the people complaining that it’s impossible just don’t know the rules as well as they think they do. I think this is nieve of you. If you continue to interview physicists about this you will get the same story over and over again. You ARE breaking the laws of physics.
>> ‘I’m not disputing that wind starts the cart moving, but once it crosses the zero point, there can be no doubt that wind has nothing to do with it.’
“And yet for some reason the cart stops when the wind stops."
I thought I had addressed this clearly but I’ll try again. When your cart is doing 15 mph it’s speed is ZERO relative to the air (assuming a 15 mph wind as per the video). I repeat, at that speed, you are not moving THROUGH the air. You and the air are buddies enjoying the same state of motion. Wind? What wind? This is the absolute truth of relativity of motion, I can’t emphasize this enough.
As you increase speed beyond 15 mph the only wind you are experiencing is going in the opposite direction as you leave the air behind you. Upon reaching 30 mph your cart is now moving through the air at 15 mph. I don’t know how fast your prop is spinning at this speed but I will call it (X)rpm.
Now, adjust your gear ratio so that if you push start the cart to 15 mph, at that speed the prop will still be rotating at (X)rpm. Thus on a windless day, you will be going 15 mph faster than the air and with a prop rotation of (X)rpm. Your interaction with the air will be IDENTICAL to what it was when the wind was 15 mph and the cart was 30 mph and guess what? When you let go of the cart, it will not stop (unless the wind starts blowing, hee hee).
18 May 2011 at 3:18 pm
Well yes, it's a propeller but that's not what I meant.
What I was trying to articulate is that the horizontal component of the normal to the prop blade plane (in the wind frame) is always of a negative magnitude to the wind speed relative to the ground. That is, the turning prop always pushes backward no matter how fast the vehicle moves. Thus the top speed of the cart is proportional to the wind speed, discounting friction etc.
If the wind stops this component is now in the opposite direction - ie toward the front of the cart - so it slows down even though at this point the prop is acting like a weak turbine, to use your term.
Actually I'm not sure that clarified anything at all but I lack the technical language skills to do better. I wish I could do better. It would be disappointing if people just accepted this on faith without understanding the mechanics that make it work.
You do realize that the turbine version moving upwind faster than the wind will open a whole new can of worms don't you?
18 May 2011 at 4:56 pm
>> "Your rotor is an “over-unity” device."
Not so much. I designed the thing based on the typical mundane physics principles known to all high school physics students. And then it did exactly what it was designed to do - and exactly what the simulations said it would do. No "over-unity" involved.
Don't you think I'd be the first to be claiming over-unity if I'd discovered it?
>> "You ARE breaking the laws of physics"
You CAN'T break the laws of physics. Whatever happens - those are the laws of physics. We don't get to make them up.
You claim that the cart can be geared to operate in no wind (i.e. air not moving relative to the ground). I am here to tell you that's simply not true. I have posted a sequence of build videos on youtube that will take you through the construction of a small working model. I challenge you to make one and demonstrate it working in no wind.
>> "It would be disappointing if people just accepted this on faith without understanding the mechanics that make it work."
I agree. But it would be even more disturbing if people re-wrote the already perfectly adequate laws of physics to explain it. I assure you it is easily explained with the mundane every day laws of physics we learned in high school.
>> "You do realize that the turbine version moving upwind faster than the wind will open a whole new can of worms don't you?"
That's the entire objective :)
19 May 2011 at 12:39 am
Dude, you're flatly contradicting me but offering zero explanation. You have not legitimately addressed any of my arguments. What a disappointment.
"You CAN'T break the laws of physics. Whatever happens - those are the laws of physics. We don't get to make them up."
This is a silly statement. As I clearly discussed, and as you well know, the law I claim you are breaking has never been proven. If there was ANY reason to believe that breaking the 2nd law of thermodynamics was synonymous with breaking the law of conservation of energy, then it would be reasonable to insist the 2nd law is absolute, but this simply isn't the case. There is only the weak and actually absurd assertion that no one has ever observed an exception.
"You claim that the cart can be geared to operate in no wind (i.e. air not moving relative to the ground). I am here to tell you that's simply not true."
And you base this assertion on what?
"I challenge you to make one and demonstrate it working in no wind."
I'm working with a friend on a different application that will demonstrate the same principle so we should see in a few weeks.
19 May 2011 at 1:14 am
>> "Dude, you're flatly contradicting me but offering zero explanation."
I am offering an explanation. I pointed out that I designed this thing using the known laws of physics - and that it does exactly as predicted by those laws. That is about as good an explanation as you could hope for that it does not require violating the 2nd law of thermodynamics.
You on the other hand have claimed it violates the 2nd law with absolutely nothing to suggest that's the case.
>> "I'm working with a friend on a different application that will demonstrate the same principle so we should see in a few weeks."
I am highly confident that you won't develop anything that violates the 2nd law of thermodynamics - but I am eager to be proved wrong on this point.
If you claim this cart can operate in zero-wind, the best way to prove that is to build a small model of it and make it do so.
19 May 2011 at 2:28 am
jswendell...
The body of evidence (observationally and experimentally) point firmly in the direction that the 2nd law of thermodynamics is correct. Should you (or anyone else for that matter) be able to provide a repeatable, verifiable, factual demonstration of an instance where it does not apply I will be first in line to congratulate you and then go back and scrap the approximately 200 years of physics work that relies upon it. And no, the Blackbird is NOT one, it does work on "mundane" physical principles whether you can wrap your head around the process or not makes no difference.
Also, I will also gladly state that internal combustion engines must run on fairies since they can no longer rely on the second law for their basic function. In fact the sun may have some issues here as well... and the planet will quickly become uninhabitable due to runaway heating... but hey! if you can prove the reasoning and, much more importantly the MATH and observations of the entire physics exploring world wrong then I'm with ya. But so far, your simple reliance on what you call logic is a weak argument indeed.
Science, as I'm sure you actually know, is not faith. Science adjusts its views based on what observed. Faith denies observation so belief can be preserved.
I have more to say but must run. Later then,.
19 May 2011 at 8:28 am
Mr. Stark,
Your criticism of my criticism of the 2nd law is entirely spurious. As I hope you know, the essence of the 2nd law is that energy ALWAYS moves towards equilibrium. If the 2nd law could be broken, this in NO WAY implies that energy NEVER moves towards equilibrium as you have ludicrously suggested as the only other possibility.
"But so far, your simple reliance on what you call logic is a weak argument indeed."
If this is true, then you should have no trouble pointing out the flaws in my logic. I would love to see you attempt this.
Mr. Spork,
"I pointed out that I designed this thing using the known laws of physics - and that it does exactly as predicted by those laws. That is about as good an explanation as you could hope for that it does not require violating the 2nd law of thermodynamics."
This is an assertion, not an explanation. You haven't even attempted to confront the logical principles I laid out. Did my explanations go completely over you head or did you just not bother to read them?
"You on the other hand have claimed it violates the 2nd law with absolutely nothing to suggest that's the case."
Are you kidding? I gave a detailed explanation that you have thus far ignored completely. Don't pretend to have revealed the logical fallacies in my thinking when you have ignored my detailed explanations completely.
Look, even if I am totally wrong, it is ludicrous for you to assert that, while failing to respond to any of my points. If you're going to continue to hash this out with me, at least put on a good show. I feel like I'm arguing with a brick wall.
19 May 2011 at 9:29 am
jswendell, did you watch this? http://www.youtube.com/watch?v=k-trDF8Yldc
Perhaps it would help to think of it this way. If there is relative motion between the air and the ground, then there is the potential to extract energy. It does not matter how fast the cart is moving relative to either one, as long as it has an interface to both (via the prop and wheels respectively).
19 May 2011 at 10:30 am
Microfrost,
I'm going to have to think about his for a while. I'm not yet convinced this analogy is directly applicable to the wind cart. But it appears likely that I will be trying to scrape egg off my face for a long time, or wear a sack over my head or at least move to another part of the Internet where nobody knows me.
19 May 2011 at 12:42 pm
jswendell, I'm more than a little tired of you making false claims about what I have or haven't responded to. When I claimed I could make a vehicle that is powered by the wind and goes directly downwind, faster than the wind, the onus was on me to prove that. I did so. I did it through analysis, then by building a small working model, and finally by building a manned vehicle and establishing a world record in front of critical 3rd party witnesses.
It is your claim that my vehicle violates the 2nd law of thermodynamics. I've explained to you why I'm confident that it doesn't. But now the onus is on YOU to prove your assertion. You make the equally bold assertion that the cart can operate with no wind. I assure you it cannot. I think most would agree the onus is on YOU to prove that it can.
I've told you how to prove your assertions. I've posted detailed videos showing how to make an inexpensive working model of the cart. The argument we are having is fruitless for reasons I needn't go into. I leave it to you to prove your assertions if you hope for me to believe them.
>> "it appears likely that I will be trying to scrape egg off my face for a long time"
There is no shame at all in being wrong. I think there is some shame in the approach you're taking with us. Prove your assertions and I will be happy to admit I was wrong - with no shame.
19 May 2011 at 2:26 pm
I concede defeat.
I was arrogant and thought I had genuine insight about this faster than wind phenomenon. I carelessly drew false conclusions about the nature of this phenomenon because of strong preexisting prejudices about the second law which I still believe is fundamentally circumvented by the airfoil. However, now that I've made a complete ass of myself, I can't expect you to continue to debate that point with me, not that you ever tried, but if I had been in your place, I probably wouldn't have bothered either.
Anyway I apologize. Now that I recognize that the wind is powering your cart I see everything from a different perspective. I treated you like you were a chump when in fact I was the chump.
When I began posting to this page, I did not realize I would wind up talking to the actual designer/builder of this cart. I feel especially bad that I made such a fool of myself because, well, I admire you for what you've accomplished. Not only did I misunderstand how your cart works, but when you didn't agree with me I was frustrated and angry that you so flippantly disregarded what I was saying. Now I'm like, oh, maybe I shouldn't try to tell an engineer how his stuff works.
While I'm not really in a position to ask you for anything at this point, I still wish you would respond to my critique of the 2nd law. You only addressed this once and I believe you've missed the point.
>> 'Those giant airfoils are valving energy out of the air to lift the plane'
"Nope. The wings are simply a much more efficient way to put that energy to use if you want to lift a plane."
In the example I gave, a plane pointed vertically with it's prop generating maximum thrust, it appears to me that 100% of the thrust is going into lifting the plane and yet the plane cannot be lifted this way. Since you can't improve on 100% efficiency (without going over-unity) your statement doesn't make sense to me. If I am wrong about this too, I would like to understand why. Or maybe somebody can point me to a video that will clear this up. It wouldn't be the first time :)
19 May 2011 at 3:46 pm
There's no defeat because it wasn't a competition. You were open-minded enough to consider the evidence and reach a new conclusion. Also, no apologies are necessary.
As to the airfoil circumventing the 2nd law of thermodynamics, I can say with relative certainty that they don't do that.
>> "I was frustrated and angry that you so flippantly disregarded what I was saying."
I'm sorry if it seemed that way. I honestly considered what you had to say, and I felt I explained why I disagree. Obviously I haven't explained it well enough.
>> "In the example I gave, a plane pointed vertically with it's prop generating maximum thrust, it appears to me that 100% of the thrust is going into lifting the plane and yet the plane cannot be lifted this way."
True enough. But you simply have the wrong tool for the job. Clearly it's not an issue of using an airfoil vs. using a prop - since a prop is really just a pair of wings spinning in a circle. It's just that all your energy is being wasted by making a relatively small amount of air go really fast. You're trying to climb a hill in top gear.
Here's the simple explanation... For a plane to hover you want static thrust. That's raw pulling force without the plane moving forward. Picture a plane on the runway with its brakes locked and the engine at full revs. That's static thrust.
Thrust is proportional to mass * delta_velocity
in the case of static thrust delta_velocity is the exit velocity.
Energy is given by 1/2*mass*exit_velocity^2 (that's exit velocity squared).
So it's easy to see that a given amount of static thrust can be achieved by moving more mass (i.e. more air) through a smaller change in velocity.
Because energy is proportional to velocity-squared, it becomes clear that doubling the mass and halving the velocity will save you a LOT of energy.
Or looking at it another way, an engine of a given horsepower could change props to a longer slower moving prop so that it only added half the velocity of the first prop - but did so to four times the mass. Clearly if we divide delta_v by 2 and multiply mass by 4 we get twice the static thrust - and we do it with no more energy.
So we can either lay the plane on its belly and let the long skinny wings do the heavy lifting, or we can put a really long slow turning prop on it and let it hover. Either way it's simply a long set of wings moving relatively slowly. In other words we'll climb the hill in low gear.
The shorter prop/wing is simply wasting a lot of energy by making the air go a whole lot faster than we need it to go.
>> "Since you can't improve on 100% efficiency (without going over-unity) your statement doesn't make sense to me."
Your point was that 100% of your thrust is trying to lift the plane. That's true. In a sense you have 100% efficiency there. What your not considering is how horribly inefficient it is to generate that thrust with a short wing. Efficiency is a weird and somewhat arbitrary thing. You have to define your denominator - and in this case it's not a question of how much of your thrust is being used to lift the plane, but rather how effectively you used your power to make thrust. Think of thrust as the by-product of making air go fast. You can get a whole lot more of that by-product with a long, slow-moving wing.
>> "If I am wrong about this too, I would like to understand why."
Let's start with the above and discuss it. Fair enough?
19 May 2011 at 4:03 pm
jswendell,
I should point out that I've been through this downwind discussion hundreds of times. I've been treated FAR worse by many people than you treated me. For the most part, when those people finally come around, they follow a pretty predictable and disappointing pattern. They explain that the problem is that I explained it all wrong, and they then go on to give me the proper explanation (that they had to figure out for themselves). Their "proper explanation" is invariably hopelessly flawed.
Out of all those discussions it's been extremely rare for someone to simply say "I got it wrong - and I apologize for being condescending". You're in the top five in that respect - and that's worth a lot of points in my book.
20 May 2011 at 2:06 am
jswendell -
I do apologize if I have offended, thats never my intention though it is occasionally my outcome!
I'm glad to see you've got the concept of how the Blackbird does it's thing - it really is a very tricky concept to grasp! Took me a good couple of hours of looking at it and doing back of the napkin calculations to be sure I was understanding what I was seeing and I do this stuff every day! Even then I really only stumbled upon my understanding in one of those "eureka!" moments - I literally turned one of my diagrams upside down and it fell into place in my mind like a puzzle piece. Love it when that happens. Without that piece of serendipity I likely would have spent a few more hours slogging through to understanding.
I'd love to have a long discussion about the ramifications of the 2nd law and why it must hold true for much of the modern world to work but my schedule just doesn't allow for it today. I'm all for testing and questioning the laws of physics - thats what physicists do every day if they are earning their pay. Who knows, perhaps you do have an insight to a flaw in the 2nd law - but I have to say that at this point that is quite unlikely. Simply because every observation ever made in an attempt to update the 2nd law and or disprove it has only served to confirm it further. Every single one. We're talking millions of experiments and observations here. While there may be a situation where entropy and equilibrium are not the outcome of a system it certainly doesn't seem to be the case in any frame of reference anybody has ever found. Doesn't mean it doesn't exist though. After all, we never actually prove anything in science, we only disprove things. So far, we've never disproved the 2nd law and a great many have tried.
I will ask a question though - and please don't be offended - are you perchance an engineer by trade? I only ask because most of those I've seen spend many a day trying to break the 2nd law seem to be engineers. I have a feeling that the idea of the 2nd law irks them since it means there is a limit to what they can create! I can understand that totally... it's why I spend my time in the theoretical world instead! ;)
20 May 2011 at 7:28 am
This simple mechanical demonstration in the video posted by Microfrost should be standard viewing for anyone who questions what is happening with the wind carts. I couldn't believe my eyes at first. I had to watch the video over and over and do a lot of thinking before I could comprehend it fully. But I don't think anyone could ask for a more concise explanation of the principles involved. Sometimes a video is worth 10,000 words.
"Let's start with the above and discuss it. Fair enough?"
Fair, would be if you refused to answer any more of my questions. This is GENEROUS! I won't respond to what you've said until I've had the time to think it through carefully. Mr. Spork, I really appreciate that you're taking the time to do this.
Mr. Stark - I am not an engineer. I'm just some guy who likes to think about stuff. I should have (perhaps it's not too late) become a serious student of physics since it fascinates me, but I have an irrational fear of math. I never made it past Calc II and have subsequently forgotten to the point where my skills don't go beyond simple algebra.
This of course makes it all the more embarrassing that I would get caught wrongfully telling an engineer that I know more about the contraption he built than he does. Quite frankly, I don't think I've ever been more embarrassed in my entire life.
I do believe that there are some fundamental principles in physics that are so straightforward and logically transparent, that advanced mathematical knowledge is not necessary to understand what is happening. I always strive to reduce any problem I'm confronted with to it's simplest form, which I think I have a special knack for.
I'm used to being in the position of seeing the obvious when others are blind to it. So I've developed an arrogance that in this case was grossly misplaced. Arrogance, when it is justifiable makes you an asshole. But when it is not justified, it simply makes you an ass. So I stand, as ass-faced as I have ever been in my life.
Finally, I don't deny and have never for a moment believed that the 2nd law was fundamentally faulty. It's clear that it accurately describes the natural tendency of energetic flow. I only have a problem with the idea that this is the ONLY way energy can behave.
James Clerk Maxwell is considered one of the greatest physicists of all time and it was he who proposed that the 2nd law could be circumvented. Given that Maxwell's concept has never been proven to be flawed, it seems to me that it could be just a matter of time before nano-technology makes it possible to literally create "Maxwell's demon" in physical form. "It hasn't been done", is very different from "it can never be done".
20 May 2011 at 2:02 pm
>>"This simple mechanical demonstration in the video posted by Microfrost should be standard viewing for anyone who questions what is happening with the wind carts"
Probably so. Michael C has been a part of the on-line DDWFTTW community for probably a couple of years, and has made several extremely instructive videos. Some people look at them and it clicks. Unfortunately, some people say that Michael's carts have nothing whatever to do with the DDWFTTW carts. There are also folks that claim the carts operating on a treadmill have nothing to do with the DDWFTTW carts. One of the things that has amazed me about this brain-teaser is just how different everyone is in how they learn. We've got dozens of ways of explaining it, and none seem to stand out as the best way.
>>"Mr. Spork, I really appreciate that you're taking the time to do this"
No "Mr." - it's just spork - with a little s. I'm happy to do it. I enjoy these sorts of discussions.
>> "Quite frankly, I don't think I've ever been more embarrassed in my entire life"
Then you've had a pretty good life :)
>> "I do believe that there are some fundamental principles in physics that are so straightforward and logically transparent, that advanced mathematical knowledge is not necessary to understand what is happening."
A good instructor can teach you an enormous amount of physics without getting into complex math. Perhaps the best I've ever seen is Richard Feynman. If you haven't seen his lecture series, you need to watch them right now. Bill Gates posted them for everyone to see for free: http://research.microsoft.com/apps/tools/tuva/index.html
>> "Finally, I don't deny and have never for a moment believed that the 2nd law was fundamentally faulty. It's clear that it accurately describes the natural tendency of energetic flow. I only have a problem with the idea that this is the ONLY way energy can behave"
I heard a physicist interviewed on a podcast a few days ago that was saying some pretty darn bizarre stuff about the nature of the universe. Not the "observable universe" but the whole universe. There are some things we just don't know, and perhaps never can know. He seemed to suggest that on the scale of the entire universe, perhaps the 2nd law of thermodynamics doesn't really apply. I found it absolutely fascinating, but I listen to these podcasts while driving. I wouldn't swear I got it right.
>> "James Clerk Maxwell is considered one of the greatest physicists of all time and it was he who proposed that the 2nd law could be circumvented."
I'm not sure, but I think Maxwell's demon is a lot like Schrodinger's Cat. Schrodinger didn't think the cat was truly alive and dead at the same time. I think it was more illustrative that physics on the subatomic scale doesn't look much like the intuitive physics we see on an everyday scale. I believe Maxwell's demon is also a sort of philosophical question or musing on Maxwell's part - more than Maxwell questioning the 2nd law. But I'm getting out of my area here.
20 May 2011 at 5:18 pm
Ahh yes... good old Maxwell's Demon. Indeed Maxwells' Demon has actually been realized - starting around 2006 if I recall correctly - in the form of a process called single photon cooling - google it. It can be an interesting read. The basics can be grasped without scary math but you would need some fairly heavy duty maths credentials to really get into the guts of it.
In single photon cooling (in VERY basic terms) you have a wall that allows atoms to pass through in only one direction. This actually causes an entropy imbalance in a closed system between the 2 sides of the wall and appears to violate the 2nd law! However... it turns out that when the atoms pass through the wall (our Demon) they randomly dislodge a photon. This photon carries information about the turning point of the atom. That means that information about the energy of the atom has been transmitted which also means we have a change in entropy. It turns out, if you do the math, that the entropy created by the information provided by that photon exactly balances the entropy imbalance of the two sides of the wall.
This illustrates what a great many physicists believe is the flaw in Maxwell's Demon - the Demon itself must effect entropy to decide which molecules pass through the door. Still, there are others who will argue that that belief is based on accepting that the 2nd law is immutable and therefore a circular bit of reasoning.
The real problem here is that Maxwell's Demon lives only in one place - perfect physics land! This place only exists in the minds of physicists... at least until a valid grand theory of everything is found. At that point our thought experiments can take into account all of the variables we have yet to learn and become accurate representations of the physical world! Until then we have to make do with approximations of the real rules of the universe... approximations that allow for Maxwell's Demon, Schrödinger's Cat, and a myriad of other colorful thought experiments to hold regular Saturday night keggers in the minds of undergrads everywhere! ;) Well, with the Cat you can never be sure if he's actually there or not...annoying little bastard.
So while there are a few things that come very close to violating the 2nd law...so far none of them actually do. Admittedly it sometimes takes awhile to discover where the rest of the damned entropy is but, so far, it's always been found!
Still, I will admit that it's not impossible! FSM knows that physics is no more immune to refinements and even complete upheavals in theories, laws and models than any other science is. Typically though, we find that the rules that have survived largely intact for a few hundred years aren't terribly likely to be found completely wrong - small refinements to the understanding (like information changing entropy) sure... but throw the baby out with the bath water stuff (which over-unity would be) is just not likely at all.
20 May 2011 at 11:30 pm
>> " Indeed Maxwells' Demon has actually been realized - starting around 2006 if I recall correctly - in the form of a process called single photon cooling"..."It turns out, if you do the math, that the entropy created by the information provided by that photon exactly balances the entropy imbalance of the two sides of the wall."
Ah yes - this is vaguely familiar.
>> "This place only exists in the minds of physicists... at least until a valid grand theory of everything is found"
I have a kitesurfing/hang gliding buddy, Garret Lisi, that just may have that theory. http://en.wikipedia.org/wiki/Antony_Garrett_Lisi Unfortunately, his math gets beyond me pretty quickly. Fortunately, there are plenty of folks considering his theory that can follow the math.
>> "FSM knows that physics is no more immune to refinements and even complete upheavals in theories..."
Flying spaghetti monster?
22 May 2011 at 2:54 am
Well, do you know of any other variety of Spaghetti Monster? I've only seen the flying type but I'm open to the possibility of others... Perhaps a Pogo-Sticking Spaghetti Monster is out there somewhere? ;)
You know Lisi? Must make for some fun conversations! I admit I've not had time to delve into his work in a more than cursory way but it is definitely interesting! The idea of a 4 dimensional base manifold super-connection is quite intriguing. I probably don't have the chops to make it all the way through the work in any quick way though so my curiosity will have to wait until I have some real time to spend on it. I know there's a few other folks working on the idea's he's put forth as well. I have to admit that I like his open notebook approach to things and hope it catches on with more theoreticians and scientist in general. Alas, it probably won't, with more and more of the research being funded by interested parties (read corporations) instead of pure science benefactors. One can hope though!
Out of curiosity... what did he initially think of DDFTTW? ;)
-Stark
22 May 2011 at 6:02 pm
If I recall, the first he'd heard that I was working on DDWFTTW was at the Google science conference last year. At that time I don't think he had any doubts or any struggle understanding why this should be just fine from a physics perspective. He and I had been on hang gliding trips together years earlier, and sort of caught up again at the conference. Since then we've had a chance to do some kitesurfing at his home site on Maui. Personally, I quite like his approach to science - and life.
23 May 2011 at 9:28 am
I imagine Harold Camping is now experiencing greater embarrassment than I can comprehend.
23 May 2011 at 4:40 pm
They asked us to display the cart at Maker Faire. Just got back. Long weekend. We won the Editor's Choice award. Pretty cool :)
3 June 2011 at 10:24 am
I'm back, hope it's not too late. I got distracted by life but I still have some questions about this.
' it appears to me that 100% of the thrust is going into lifting the plane and yet the plane cannot be lifted this way.’
“True enough. But you simply have the wrong tool for the job. ...You're trying to climb a hill in top gear.”
But that “wrong tool for the job" is the only source of fuel supplied energy. And the plane IS able to fly. If the wings are not “over unity” then all they can do is convert SOME of the energy provided by prop (horizontal thrust) into vertical thrust. If the props static thrust is insufficient to lift the weight of the plane directly, the energy can only decrease by the time it has been converted to vertical thrust by the wings.
Are you saying then that the prop produces MUCH more thrust and/or is much more effiecient when the plane is moving?
“The shorter prop/wing is simply wasting a lot of energy by making the air go a whole lot faster than we need it to go.”
But it’s only wasting the energy when the plane is not moving? Above 54mph (a Cessna 172‘s stall speed), “the shorter prop/wing” is no longer “wasting a lot of energy"? Am I understanding this?