Directly downwind faster than the wind (Pt. 7)

[Recursive Prophet]

@Semper: Can't really answer your question. All I know is what I read at TR about Eric and his cousin trying to get Prof. Kammen to invite spork to speak at Berkeley. Do keep checking there though. I sensed a recent disturbance in the humberverse that may bring spork's Dr. Moriarity back soon, and of course if that happens we could be in for another 6k run of replies.

[spork]

@Semper: Can't really answer your question. All I know is what I read at TR about Eric and his cousin trying to get Prof. Kammen to invite spork to speak at Berkeley.

I just recieved word that Dan Kammen chooses not to comment. I guess I'll take that as a big step in the right direction seeing that his previous comment was "can't be done".

[Recursive Prophet]

Well it's been confirmed. Humber didn't die at Reichenbach Falls, and is back!! Since he joined in the ddwfttw thread at TR it has matched it's 5 pages of replies a day performance that we witnessed here at RDF before he was banned, and it is a much smaller site. Some very knowledgeable newcomers there, along with many of the original cast from here and JREF where this strand originated.

Anyone interested in finding out why with humber on board this topic has broken the activity records on all the 3 different science forums where it has appeared, this is where humber accepts his first challenge on TR. I would also note that without any nannies around to slap his wrist the sporkster is back at the top of his game, and JB seems determined to finally establish through testing that ddwfttw has been proven true.

Mac Guana will be giving a presentation to the Danish Society of Engineers on 9/13 that will include ddwfttw. Their response could be quite elucidating. And of course we have also heard from a Nobel winning physicist that the ddw-directly down wind-part is a violation of conservation of energy, and humber and an outspoken ally, Harold Bricer, believe likewise. Best strand I've ever encountered in the cyberverse, and it is again fully geared. A must read for those into aerodynamics, physics, sailing, or geek humor/drama at its finest.

[Recursive Prophet]

UPDATE FOR MAD CARTEERS: I got the date wrong for Mac's presentation; it was this week I believe. PLEASE let us know how that went Mac, especially wrt to any comments on the prop cart you made and tests you've done. Sure hope you'll join in the continuation of this discussion at TalkRational. (link above) If you're too busy right now post it here and I'll see it gets to TR. How did your team do in the race?

For any others who followed this cyber-strand earlier, mender is conducting a new test proposed by Christoph Harold, and it should appear on YouTube soon. Hopefully spork will appear there soon also, with an experiment suggested by humber that proves Harold's claim the cart could fit up spork's ass sideways was false.

[DainBramage]

Finally! I still want to go back and at least read this whole pt.7. I started at pt.1, and got to page 8 before realizing it was a recurring loop. I went "last page, first page" to catch up. I hate being the guy who starts with "I don't know if this has been said, but..."

Anyway, of course it works. It took me the first 4 posts to get which way the drive force was(wheels to prop)then it all made sense. Though I really would have liked to learn every nuance of the "Humberverse", that would likely have given me brain damage anyway. But what I did read brought tears to my eyes. He must be a politician, they don't have to be right, just sound right enough for the ignorant.

The one thing I didn't see posted, is that it's not about wind speed, but about energy extracted from moving air. Whether or not it self-starts seems a matter of initial wind force on static cart(prop, frame, and all)being sufficient to overcome stiction, which is always higher than once the object is moving. Please correct me if I'm wrong, but I assume it will start in a strong wind?

That it will even move forward on a flat treadmill proves it's overcoming internal losses and then some. If you put a scale behind it to read pulling force, it goes up if you increase belt speed, does it not? So long as the speed increases slow enough for the cart to "catch up". But I didn't mean momentary. Any increase in belt speed will result in more forward pull, once a balance is again achieved? Also, the parasitic loss, as a % of total force, gets lower and lower as belt(or wind)speed increases, thereby improving efficiency.

A thought; sail flaps that would catch the wind from behind, yet lay flat when wind speed was passed, would show when it reached wind speed as well as helping it start by increasing initial "grab" with no loss once wind+ speed was achieved. Google "check valve VAWT" if I wasn't clear.

I vote the "Best comment in Thread" award goes to whoever said "I know you've proven it in practice, but does it work in theory". It's like going online to see if it's going to rain, then hearing the rain start while you're looking it up. Sticking your head outside and looking might be more effective sometimes.

Edit: The first line in my sig might come in handy here.

[DainBramage]

Only 2 pages behind now, and I see many of my thoughts have now been covered.

One point of note: I've pretty much given up on Mythbusters, because they're either stupid, or pretending to be. When they couldn't make an explosion with gasoline fumes, or a Bic lighter, both things I'm quite capable of myself(sometimes by accident ), I lost confidence in their ability to prove/disprove anything.

Nevermind the nonsense they went through about whether or not drafting saves gas.

They needed a test for that?

[Michael C]

Latest news! spork and JB have teamed up with a professor and students from San Jose State University in order to build and test a ride-on cart. They've started a blog: http://www.fasterthanthewind.org/

[DainBramage]

:sunny:

Latest news! spork and JB have teamed up with a professor and students from San Jose State University in order to build and test a ride-on cart. They've started a blog: http://www.fasterthanthewind.org/

I just went there and read the problems they're having selecting a trans system. I have 2 thoughts on that.
First, while a twisted belt is very inefficient, a twisted chain might do the trick. My first thought was to use a somewhat worn bicycle chain, or two spliced together for length. They have a lot of flex built in, even when new, a used one should twist 90 degs. in that distance without much drop in efficiency.

Second, what about a heavy duty version of the chain you pull to turn a light on? I don't know if this can be had in sufficient strength, but if so, it could be run twisted with almost 0 loss.

Just thinking out loud...

Should I put it on their "comment" spot?

[DainBramage]

<something equivalent to>"I still don't get it"

Is it possible that you still don't get that the power transmission is opposite for an upwind and downwind cart?
Upwind cart=turbine to wheels
Downwind cart=wheels to prop

@RP: The t-mil is perfectly analogous, if the belt was long enough, it would work exactly the same as open air.
Are you going to keep picking nits because the equipment to test that is not easily available?

A slidewalk might work, if it was long enough, and fast enough. Unfortunately, those only exist in places that are not likely to be willing to let these toys be tested.

[Recursive Prophet]

@Semper: Do keep checking there though. I sensed a recent disturbance in the humberverse that may bring spork's Dr. Moriarity back soon, and of course if that happens we could be in for another 6k run of replies.

Chalk up another prophecy fulfilled. Yes humber is back, and the thread is on pt. 5 now and has well over 7k replies.

to the jungle, Dain, where you can get any reference frame you want but you’re never gonna get it for free. Humber will fight you all the way, if you’re worthy.

As you can see, after humber was banned the thread died here and most of the action now is over at TalkRational. In fact they’re discussing the construction of the cart there right now and you really should join in. It has also been taken off moderated status recently at JREF, so there’s a lot going on there in the last 2 days also. If you scroll up and click the link in spork’s sig, it will take you to the start of this thread here. Scroll just below to my first post and there are links to the entire history of this strand.

If you went back to JREF you’d see I not only believe ddwfttw is possible, but have an outstanding bet on it with a friend. Mac G. has given his presentation now, and based on the acceptance of the Danish Society of Engineers of d..w I was going to try and collect on my bet. But as this is a good friend, I’ve decided to wait and see what spork and JB come up with in this latest project. Don’t assume you know my thoughts on this based on what I say on the boards.

I do understand the argument for the treadmill. I believe it is equivalent to the cart in the wind. Yet there are long belts at most airports and in factories, and still nobody has shown one advancing against it minus any kind of tether. The best display we have of a cart in the wind is Jack Goodman’s from 2 years ago. One of the most renowned physicists in the country stated it violates conservation of energy. And while as spork says he apparently declined to comment further, he didn’t recant his original position as far as I know.

I’m afraid like many such debates this one is going to end as a semantics dispute unless spork’s latest project comes up with some verifiable test results. Something along the line of "if the 'apparent wind' from the movement on the belt has no actual parallel with natural wind-produced from high and low pressures meeting-then you can only claim ddttfttb has been proven. I actually feel pretty confident now spork will pull it off, or perhaps Mac now that he has built one, and may double my bet. Until then, while all the ducks seem to be lined up, remember the many physicists that bought ‘cold fusion.’ When presented with a subatomic duck, wait till you hear it say quark quark.

[DainBramage]

Obviously, the perfect outdoor test would require perfect(unvarying)conditions to exist outdoors, which they never will.
If the cart exceeds average wind speed over distance, that's as good as you're going to get. The problem then becomes, finding a way to track average wind speed at cart level. Smoke, or a neutral balloon, would only work if the vector was perfect, and perfect over enough time to give good data.

What they need for a slidewalk type test is to install an R/C steering control to keep it on the belt.

[Recursive Prophet]

You really should join in the discussion at TR DB. Lots of discussion about how the measurements will be done, but I can tell you they are looking at wind speed and distance, and I agree that's a pragmatic way to do it. The closed airport runway they found would be as good as you could get for such a test in the Bay area.

Heard from Mac recently, and he hopes to video and post on YT an upcoming presentation that will include d..w. Spork and JB's blog is starting to get some traction, and I'd encourage you or any others interested in this subject to sign on at the link Michael posted above and help show their sponsor there's a lot of interest in this project. You can also post any suggestions/questions there, and get logged in with just a few clicks.

[Mac Gaunaa]

Hi all,

I have now finally managed to shoot a video of a slightly updated version of the presentation I gave Sep. 24th at the 2009 Aeolus wind turbine car race in Stauning (Denmark) for the Danish Society of Engineers. The original title of the presenation was "The Aeromechanics of Wind Turbine Cars", but perhaps a better title would have been "Travelling in line with the wind using the wind" because I devote almost half of the time to talk about the DDFTTW (Directly Downwind Faster Than The Wind) vehicles, which has been rather heavily debated around here. For this reason I posted the video on Youtube for your viewing pleasure (or pain). The full presentation is close to 55 minutes, so please take your time when viewing it. Due to the constraints of youtube I split it into 6 parts.

Part 1: Introduction and a bit of history: http://www.youtube.com/watch?v=4ZjX_DIosM8
Part 2: A teaser & How it works #1 (Basic principles): http://www.youtube.com/watch?v=gN4QLOBl1CQ
Part 3: How it works #2 (The main result): http://www.youtube.com/watch?v=JUwZmUjjgn4
Part 4: How it works #3, How fast will a WT car go and DDWFTTW theory: http://www.youtube.com/watch?v=VFXKLGlBO2I
Part 5: DDFFTW practical proof and attempts at easily understandable physical explanations: http://www.youtube.com/watch?v=qssCU_GeU3g
Part 6: Advanced topics, further reading material and closing: http://www.youtube.com/watch?v=Km9sW3kUfFw

There was quite a few spots where for some reason the things I had planned to say came out more or less reversed. However, I still think my view of how things are connected does come through, so I hope that you will enjoy the videos anyway.

-Mac G

[Recursive Prophet]

Thanks for sharing these videos Mac. I have viewed them all and found them both interesting and informative. Glad to see you've logged on at TR, for as you can see this topic is about as dead here as on the Physics Forum.

For any that still look in on this thread, spork and JB are moving ahead quickly with their Ride Like the Wind (only faster) project building a drivable sporkmobile in conjunction with a physics class at SJSU. It's easy to sign on as a follower and watch their progress, and suggestions on the car's construction are welcome. Just click here.

[Recursive Prophet]

So here's a pic from the Ride The Wind Faster team's frame for their prop powered car, which they put together last weekend. These guys are serious scientists, and this project could well be history in the making. The debate on whether going directly downwind faster than the wind steady state is achievable has been raging throughout the metaverse for over a year now. Even though it moved to TalkRational-see link in previous post-many months ago, it still holds the all time activity record on RDF for all science related topics. Most of it occurred in the first 2 months before the most consistent critic-humber-was banned, and it has now shattered the records at TR with over 14k replies and still going up. This project could well provide a definitive, scientifically verifiable answer and defrock an ancient sailing myth in the process.



For those that have managed to find this thread and have followed it before the move, you should read the reply by Mac G to Harold Bricer on TR. Many believe he and Christoph are the same person, due to countless similarities in their viewpoints and style of expression. In the end it doesn't really matter, and the detailed reply by Mac is quite revealing wrt to some gaps in Harold's physics. One of the best deconstructions of Harold's thinking I have read.

http://talkrational.org/showthread.php? ... post670017

[Topsy]

Even though it moved to TalkRational-see link in previous post-many months ago, it still holds the all time activity record on RDF for all science related topics.

Are you sure? I thought the WHHE thread holds the RDF science record for most posts. viewtopic.php?f=4&t=95152

[Recursive Prophet]

Even though it moved to TalkRational-see link in previous post-many months ago, it still holds the all time activity record on RDF for all science related topics.

Are you sure? I thought the WHHE thread holds the RDF science record for most posts. viewtopic.php?f=4&t=95152

I stand corrected Topsy. I haven't looked in on that thread in a while, and just within the last month it has passed the ddwfttw thread in replies. Go Algis. I like that thread, though I have only rarely posted there. Seems to me it was started back in '07 wasn't it? This one only began in late February of this year, and reached over 6k within its first 2 months. In terms of the replies per day average over that period, I seriously doubt any topic in the 3 science forums will ever come close to that record. I might also note that if we count the 14k replies this thread has garnered since moving last April to TalkRational-a site that doesn’t see a tenth of the traffic you have here-then the Aquatic Ape is still in the water by comparison. This strand has also been reactivated on JREF. So why does all this matter?

I point to the activity to show there is real interest in this subject, and would argue the content to noise is at least 85%! It’s an intriguing dialectic that is fueled by the arguments of a true contrarian who so reminds me of Mr. Tortoise in Gödel, Escher, Bach. Now it has drawn in some real expertise, and spork and JB are on track to do the first ever real scientific testing in the near future. Yet this debate is unavailable to the users at RDF, as the one who inspires the questions and explanations of this very complex aerodynamics brain teaser has been banned here. Such a loss in the name of decorum.

I had hoped some of the discussion might return here, and have posted links to the 7 parts on RDF. They no longer work, however, as it has been moved to this new sub-forum. There is no new technology wrt the cart. I is a simple geared shaft attached to a propeller. 95% of the discussion revolves around Newtonian Physics; Galilean transformations; vector analysis; and the nature of force, drag, thrust, and kinetic energy. It is in no way about technology, and I have to wonder how it ended up in this new and little viewed basement of the science section.

[Topsy]

You could send a PM to the science and tech mods and make a case for moving it back to "general science".

[Recursive Prophet]

You could send a PM to the science and tech mods and make a case for moving it back to "general science".

As you will see below, I had already done what you suggest several days ago. Russell seemed to agree with me, while Darkchilde didn't. I would invite her to present her reasons here, or we could start a thread in the other 'Tech' forum.

Those who have posted on this thread before-and there are many-would simply assume it was dormant in the archives after not seeing it in gensci. It has a more extensive history than any other thread in that forum by far, yet you would argue it is reasonable to move it to a new forum? But most importantly, on what basis would you argue it is more about technology than it is about how the laws of physics and aerodynamics apply to the equivalency between a common exercise treadmill and a very simple prop driven cart? Show me where any form of new technology is part of this discussion!!!

Hi Russell. I was curious about why the ddwfttw thread-the one that holds the activity record for all the science forums here-was moved to Tech. It's a discussion that centers around aerodynamics and physics, and there is no new technology involved, really. The idea was introduced back in the sixties, and it's a debate about whether the simple prop carts made by spork can exceed wind speed steady state directly downwind, and if it is in fact possible.

This thread is pretty dead now, but I wouldn't be surprised if it might pick up as spork is making a drivable cart. Anyway, I definitely think it would be a better fit in GS, and would appreciate an answer as to why it was put in tech. Thanks.-RP

Thanks Russell. I agree totally. I got a very different reply from Darkchilde, and thought I'd share my response below. No big deal, as I said, but it really is out of place in Tech, as are a lot of the evo threads that are now there IMHO.--RP

Thanks for the reply Darkchilde. As the unofficial text janitor for this thread, who has read all 24k replies, I believe you're very mistaken wrt the overall discussion. It's all about the physics involved. I doubt there have been more than 5 out of the hundreds of pages that are about the technology of the cart-which is quite simple-or anything to do with it's construction. This has only really come up recently owing to spork starting to make a drivable cart. This project is rarely brought up on TR where the topic is most active.

This is all a fairly moot point, as the thread has pretty much died here after humber was banned. It's now approaching 14k replies at TalkRational, a site that see's about one tenth the traffic RDF does. The content to noise ratio is quite high, but the frequent though insignificant ad homs would discourage well known scientists like Mark Drela or Dan Kammen from posting there. I had a dim hope we might extend the dialectic back to RDF, where they might feel more comfortable as insults are proscribed. It has been reopened on JREF, but humber is still there so it is back to a moderated status. Moving the thread to a new sub-forum after all this time will likely end any chance it could be revived for this purpose here.

If you looked at my earlier history on this site you would see I was able to get some internationally renowned biologists like Milford Wolpoff and David Stringer to participate in a thread I started in evo on multiregional genesis. I'm afraid RDF has now lost many of the posters that made it possible to draw in such talent, and I see a lot of them at TR. What it says to me is it's a very thin line mods must tread in implementing policy to keep the boards respectable yet allow heated debate. As Sir Humphrey Appleby once said: "It's easy to get confused by the differences between the policy of administration and the administration of policy."--RP

[Topsy]

I suggest sending a joint PM to Russell, Darkchilde and Calilasseia, summarising your case for it being moved back to General Science and see if you can negotiate via a discussion between the 4 of you.

[Recursive Prophet]

Thanks for the suggestion Topsy, and to Darkchilde for putting this thread back in this forum.

Below is a link to a long reply by Mac G to humber and the maths from his response. I think it makes a strong case for ddwfttw. If any find faults in Mac's numbers or reasoning, I hope you will post them. Asymptotic Freedom? Sal 1800? Anyone? (This looks much better using Latex, and you can read it at TR with that format just by clicking the link. Can anyone tell me if this site supports Latex??)

viewtopic.php?f=5&t=73123&start=0

PROOF THAT KINETIC ENERGY (AND INCREASE IN KINETIC ENERGY) IS IN THE EYE OF THE BEHOLDER AND THAT THAT IS CONSISTENT WITH HOW THINGS NEED TO BE (within in the frame of classical mechanics of course), AND THAT FORCES SHOULD NOT BE CHANGED IN THE TRANSFORMATION FROM ONE SYSTEM TO ANOTHER:


X: "coordinate as measured in ground attached coordinate system"
x: "coordinate as measured in system whose origio moves with the constant velocity V_x, Position of the origio of x as seen from X is X_x=V_xt+X_{xo}"

Relation between coordinates measured in the two systems:
X=X_x+x =V_xt+X_{xo}+x (EQ.1)

Relation between velocities measured in the two systems (diff EQ.1)
\dot{X}=V_x+\dot{x} (EQ.2)

Relation between accelerations measured in the two systems (diff EQ.2)
\ddot{X}=\ddot{x} (EQ.3)

From this follows that N2 looks the same in each of the two systems
F=M\ddot{X}=M\ddot{x} (EQ.4)

(This was the main point in the previous proof, so I'll refrain going in detail with this again...)

Now consider the concentrated mass M, which at t=0 is located (measured in the ground attached coordinate system) at position X_M(0)=0 and has the initial velocity (again measured in the ground attached coordinate system) \dot{X_M}(0)=V.

Converting these to positions and velocities as measured relative to the moving coordinate system using EQ.1 and EQ.2, respectively, we get

x_M(0)=X_M(0)-X_{xo}=-X_{xo} (EQ.5)

and

\dot{x_M}(0)=\dot{X_M}(0)-V_x=V-V_x (EQ.6)

If we now evaluate the kinetic energy of the mass M in the ground coordinate system at time t=0 then we get

KE_X(0)=\frac{1}{2}M(\dot{X_M(0)})^2=\frac{1}{2}MV^2 (EQ.7)

The kinetic energy of the mass M in the moving coordinate system at the same time is

KE_x(0)=\frac{1}{2}M(\dot{x_M(0)})^2=\frac{1}{2}M(V-V_x)^2 (EQ.8)

So we see that there is a difference in kinetic energy of \frac{1}{2}M(V_x^2-2VV_x) which is due to the difference in velocity of the two systems.

Now we will apply the force F to the mass M from time t=0 to t=1. We'll look at it from each of the two systems and see whether everything is consistent by doing so. If it is, then this is a proof that the forces should not be scaled when doing the transformation between two systems. We'll also see that the increase in kinetic energy depends on the reference frame, but that this also fits with how theory says it should be.

First we look at the situation from the ground fixed coordinate system. Recall that the position and velocity of the mass as observed from this system at time t=0 is

X_M(0)=0 and \dot{X_M}(0)=V

From N2 (EQ.4) we get
\ddot{X_M}=\frac{F}{M} from t=0 to t=1 (EQ.9)

Now integrate from the initial conditions to t to get the velocity
\dot{X_M}(t)=\dot{X_M}(0)+\int_{0}^{t}\ddot{X_M}(t)dt =V+\frac{F}{M}t for t=0 to t=1 (EQ.10)
\dot{X_M}(t)=\dot{X_M}(1)+\int_{1}^{t}0dt =V+\frac{F}{M} for t greater than t=1 (EQ.11)

And integrate again to obtain the positions
X_M(t)=X_M(0)+\int_{0}^{t}\dot{X_M}(t)dt =Vt+\frac{1}{2}\frac{F}{M}t^2 for t=0 to t=1 (EQ.12)
X_M(t)=X_M(1)+\int_{1}^{t}\dot{X_M}(t)dt =Vt+\frac{F}{M}(t-\frac{1}{2}) for t greater than t=1 (EQ.13)

From this it is seen that the increase in kinetic energy as observed from the ground system is
\Delta KE_X=\frac{1}{2}M(V+\frac{F}{M})^2-\frac{1}{2}MV^2=\frac{1}{2}M(2V\frac{F}{M}+(\frac{F}{M})^2) (EQ.14)

Evaluating the work performed by the force as seen from this system we get
W=F\Delta X=F(X_M(1)-X_M(0))=F(V+\frac{1}{2}\frac{F}{M})=\frac{1}{2}M(2V\frac{F}{M}+(\frac{F}{M})^2) (EQ.15)

Which is equal to EQ.14 as it should, since increase in kinetic energy is equal to work. So so far everything is fine and dandy.

Now we'll look at it from the moving coordinate system. Recall that the initial coordinate and velocity of the mass in these coordinates are (EQ.5 and EQ.6) x_M(0)=-X_{xo} and \dot{x_M}(0)=V-V_x.
EQ.4 showed that Newtons second law
is applicable in in this coordinate system in the same form (without having to take into account fictitious forces), so the acceleration of the mass M is therefore also in this system

\ddot{x_M}=\frac{F}{M} from t=0 to t=1 (EQ.16)

Note that I have used the same force here, because the forces do not need to be transformed. If they did I'd get results that disagreed in the two systems, which we will see that they do not. But that is for later. Now we'll integrate the acceleration to obtain the velocities as measured in the moving coordinate system
\dot{x_M}(t)=\dot{x_M}(0)+\int_{0}^{t}\ddot{x_M}(t)dt =V-V_x+\frac{F}{M}t for t=0 to t=1 (EQ.17)
\dot{x_M}(t)=\dot{x_M}(1)+\int_{1}^{t}0dt =V-V_x+\frac{F}{M} for t greater than t=1 (EQ.18)

And integrate again to obtain the positions as measured in the moving system
x_M(t)=x_M(0)+\int_{0}^{t}\dot{x_M}(t)dt =-X_{xo}+(V-V_x)t+\frac{1}{2}\frac{F}{M}t^2 for t=0 to t=1 (EQ.19)
x_M(t)=x_M(1)+\int_{1}^{t}\dot{x_M}(t)dt =-X_{xo}+(V-V_x)t+\frac{F}{M}(t-\frac{1}{2}) for t greater than t=1 (EQ.20)

From this it is seen that the increase in kinetic energy as observed from the moving system is
\Delta KE_x=\frac{1}{2}M(V-V_x+\frac{F}{M})^2-\frac{1}{2}M(V-V_x)^2=\frac{1}{2}M(2(V-V_x)\frac{F}{M}+(\frac{F}{M})^2) (EQ.21)

Evaluating the work performed by the force as seen from this system we get
W=F\Delta x=F(x_M(1)-x_M(0))=F(-X_{xo}+V-V_x+\frac{1}{2}\frac{F}{M}+X_{xo})=\frac{1}{2}M(2(V-V_x)\frac{F}{M}+(\frac{F}{M})^2) (EQ.22)

Again this is equal to EQ.21, so this is consistent with how we know things ought to be. Note also that the increase in kinetic energy viewed in the two systems differs because of the velocity difference between the system. This might seen tricky to some, but this is all because kinetic energy is in the eye of the beholder.

As a reassurement that we did not make any mistakes, we transform the positions and velocities obtained in the moving system coordinates(EQ.17-EQ.20) to the ground coordinate system using the position and velocity transformation equations, EQ.1 and EQ.2.

The result is for the coordinates (EQ.1 and EQ.19-20):
X_M(t)=V_xt+X_{xo}+x_M(t)=Vt+\frac{1}{2}\frac{F}{M}t^2 for t=0 to t=1 (EQ.23)
X_M(t)=V_xt+X_{xo}+x_M(t)=Vt+\frac{F}{M}(t-\frac{1}{2}) for t greater than t=1 (EQ.24)

And for the velocities (EQ.2 and EQ.17-18):
\dot{X_M}(t)=V_x+\dot{x_M}(t)=V+\frac{F}{M}t for t=0 to t=1 (EQ.25)
\dot{X_M}(t)=V_x+\dot{x_M}(t)=V+\frac{F}{M} for t greater than t=1 (EQ.26)

Please observe that EQ.23-EQ.24 are identical to EQ.12-EQ.13 and EQ.25-EQ.26 are identical to EQ.10-EQ.11. So if done correctly things are consistent no matter what coordinate system is used.

To summarize the conclusions we can draw from this little exersize:
Kinetic energy is in the eye of the beholder.
Change in kinetic energy is in the eye of the beholder.
It doesn't matter what reference system is used for compuation of the response. The result are identical if done correctly, but may look different due to the different viewpoints (reference system).
The forces does should NOT change when shifting viewpoint from one system to another.


I hope this clears up some issues.


-Mac G

[Subduction Zone]

I was just trying to get on to the Talk Rational forums and it looks like Go Daddy. com has hijacked the sight. Does anyone know what happened there?

[Mononoke]

Hey, can someone tell me what this thread is about. I tried to read the EQ on the earlier post but it was too difficult to read.

[Subduction Zone]

Hey, can someone tell me what this thread is about. I tried to read the EQ on the earlier post but it was too difficult to read.

It is about whether or not it is possible to make a vehicle that can travel directly downwind faster than the wind powered only by the wind. It can be done, it has been done by several people. This thread does tend to get a bit off track, and some people react almost violently to this idea. But ask questions and I will try to answer them.

[Mononoke]

Hey, can someone tell me what this thread is about. I tried to read the EQ on the earlier post but it was too difficult to read.

It is about whether or not it is possible to make a vehicle that can travel directly downwind faster than the wind powered only by the wind. It can be done, it has been done by several people. This thread does tend to get a bit off track, and some people react almost violently to this idea. But ask questions and I will try to answer them.

This doesn't make sense to me. I did some simple calculations please tell me where I was mistaken.

So let assume the mass of our Craft is - M
the average mass of an air molecule is - m
the velocity of air relative to ground is V_air
The initial velocity of the craft is V_i
The final velocity of the craft is V_f

So assuming N molecules collide with the sail, and with zero resistance, no gravity and 100% efficeincy.

using conservation of momentum we can get

MV_i +2Nm(V_air-V_i)=MV_f ..................(eq.1)

Now assume that the craft is accelrated to the velocity of are V_air=V_i

we have MV_i = MV_f making it impossible to accelerate the craft any further.