Down wind faster than the wind

[Thabiguy]

I don't understand. The propelling assembly - prop, it's mounting? - they are part of the vehicle and are not "moving forward" or backward, relative to the rest of the vehicle, surely? When the vehicle reaches windspeed (which it won't, as I've said) its propeller assembly is (would be) moving at windspeed. If it were moving forward at less than windspeed, it would fall off the back of the vehicle, surely?

I understand that you didn't understand; I didn't explain it particularly well. What's "moving forward" at less than windspeed is the surface which the air is pushing against - the "thread" of the propeller, if you look at it as an airscrew.

Again, the cart with the propeller is just not a good device to explain this on. It's better to start with some of the other faster-than-wind devices mentioned here that do not use a propeller. After you understand those, you should also be able to understand the propeller version and perhaps then you'll also understand what I clumsily tried to say there.

ETA: Also, Spork gave a nice explanation for the propeller version in the recent posts. Maybe that one will work for you better.

You see, I was going to object that the 'interface' with the ground is only of rolling resistance and can only slow the vehicle, but I was working on the idea of a turbine driving the wheels, and maybe that's wrong.

The rolling resistance just gets in the way and decreases performance somewhat; it's not essential to the operation of the vehicle. The essential part of the "ground interface" is the sliding friction between the wheels and the ground that doesn't let the wheels slip. Just like in car wheels.

Generally, I'd say you seem to be heading toward understanding the whole thing.

 

[John Freestone]

Probably one of the key things that suggests it's not perpetual motion is the fact that it needs a continuous supply of energy to keep going.

I put 'perpetual motion' in quotes because it's not literal. Of course there is a continuous supply of energy to keep it going. However, it's about the vector of the delivery of that energy, the force into the system.

In the treadmill example - if you have this system with, as its sole input of force the band moving from right to left, with a body sitting on it, there needs to be a force resisting the tendency of that body to move with the band (assuming it is not a perfectly frictionless contact, whereupon it would just sit there and let the band move under it). The demonstration seems to show this vehicle gaining such a resistant force - and then some more, so as to progress against the direction of the belt. Now that is what is meant by the approximate phrase 'perpetual motion'. The demonstration seems to show a body having a right to left vector force given to it (as the sole input in this case) which is somehow translated into a force right to left that is sufficient to overcome the original input.

This, AFAIK, is contrary to simple physical laws. It is as though I stood on an ice rink, and you pushed me, standing still with your back to the barrier and, instead of gliding away, I used some of your pushing energy to move towards you. The point is that the complexities or otherwise of sideways motions of bits of fan are utterly and completely irrelevant. Newton's laws do not allow for a system to do that, unless I am very much mistaken.

Do you at least understand the objection? If you have a system with the only force input from the right, you can only get a part of that system to stand still (let alone move in the opposite direction), by applying a force from the left from outside the system. There is no source of such a force, unless there is a downward gradient, or some wind, etc., etc.

I note that in one video, it is just possible that there might be a fan out of sight, which could be pushing the model, although the gradient does look correct. In another, we see behind the model, and clearly there is no fan there, just wall. However, in this video, there is much less clarity about the gradient of the treadmill. Please understand that I am not calling you (or whoever did these videos) a liar. I am saying that as far as I can tell, what I appear to see in the videos is impossible, and if it is impossible, one naturally begins to consider possible tricks that could be being employed. I understand that this scepticism may feel insulting, but I do not mean it that way. If I watch a video of someone levitating, I ask myself what the trick is. Yours seems an extraordinary claim too.

Do you see the Newtonian objection, spork?

Do you consider your machine to break known laws of physics?

Are you mystified as to how it works, or do you believe you understand it?

My apologies again if some of this is answered already. I'm trying to catch up with the thread, but there are so many distractions from the basic physics of it that it's taking some time to even find what's relevant. Airplanes on treadmills, for instance...aren't.

 

[Myriad]

Here's a link to a post buried deep in the thread, with a concise (though incomplete) compendium of non-propeller devices that show the principle:
http://www.internationalskeptics.com/forums/showthread.php?postid=4221209#post4221209

What they all have in common is that the point(s) at which the motive force is applied are translating backward (right to left, in the diagrams) with respect to the vehicle, while moving forward (left to right) with respect to the ground. In the four wind-powered ones, the sails/parachutes/vanes move left to right relative to the ground but also move toward the back of the vehicle. Thus the wind can still push them even when the vehicle is moving at or somewhat beyond wind speed.

Here's the new improved para-yoyo. I haven't heard any rational argument for why this device's predecessor wouldn't work (aside from fiddly complaints about cords getting tangled). This one is better balanced and keeps the return loop out of the way of the deployed chutes:

(The dotted lines represent pipes through which the chutes pass to keep them out of the wind on that portion of the circuit.)

The wind and the vehicle move left to right. When deployed along the top line, the chutes move right to left relative to the vehicle, but left to right relative to the ground. Thus they can be pushed by the wind even when the vehicle is moving faster than the wind.

Respectfully,
Myriad

 

[spork]

This, AFAIK, is contrary to simple physical laws.

It's supposed to seem that way. That's why I posed it as a brainteaser.

It is as though I stood on an ice rink, and you pushed me, standing still with your back to the barrier and, instead of gliding away, I used some of your pushing energy to move towards you.

All you'd have to do is lean on your skate blades and you could use that energy to go coasting right back by me.

The point is that the complexities or otherwise of sideways motions of bits of fan are utterly and completely irrelevant. Newton's laws do not allow for a system to do that, unless I am very much mistaken.

Those bits are working against the air, and using the energy put in through the wheels to do that. Newton is quite alright with it - I assure you.

Do you at least understand the objection?

Of course I do. It just doesn't seem right. But I could post another 30 brainteasers on this forum and cause just as much controversy with each.

If you have a system with the only force input from the right, you can only get a part of that system to stand still (let alone move in the opposite direction), by applying a force from the left from outside the system. There is no source of such a force, unless there is a downward gradient, or some wind, etc., etc.

But you can't think of the only force input being from the belt. This cart is being squeezed between two mediums - the belt and the wind. If we do our analysis from the inertial frame of the belt (which is perfectly valid) we find that the treadmill inputs no energy. In this frame the wind does all the work.

I note that in one video, it is just possible that there might be a fan out of sight, which could be pushing the model, although the gradient does look correct.

Yes, there could be but there's not. That's why I've posted the parts, plans, and a 10 to 1 bet for $100K that it's real. I ain't rich enough to part with that kind of cash on a lark.

I understand that this scepticism may feel insulting, but I do not mean it that way. If I watch a video of someone levitating, I ask myself what the trick is. Yours seems an extraordinary claim too.

Yes, it seems extraordinary. But in real life it's just plain old physics. You should build one and try it yourself - but do it sitting down.

Do you consider your machine to break known laws of physics?

Absolutely not.

Are you mystified as to how it works

Absolutely not.

...or do you believe you understand it?

Absolutely. And I can explain it to you. But it's better to start with simpler machines as thebiguy has suggested. This one is a tough stepping off point.

 

[Dan O.]

Over unity is actually easier to fake in a video than perpetual motion. It would look just like a negative frictional loss which is equivalent to reversal of the time arrow.

Of course, this is not what spork did.


John, how can you say that the cart cannot perform as claimed if you haven't put together a complete force diagram for the whole system?


ETA: Spork, I tried to look up the L/D numbers for your prop but all the simulations seem to assume that the prop is moving through the air. Have you got a reference for these numbers or would it be possible for you to measure them in "still" air at the RPM of the prop on your cart?

 

[John Freestone]

But you can't think of the only force input being from the belt. This cart is being squeezed between two mediums - the belt and the wind. If we do our analysis from the inertial frame of the belt (which is perfectly valid) we find that the treadmill inputs no energy. In this frame the wind does all the work.

And if you do that, analysed the system with respect to the belt, wind doing all the work, once the machine is at windspeed (assuming no losses) the wind, which you just said did all the work, isn't moving anymore with respect to the car, and thus has no effect on it. Now you need to find some force again, but you've got stationary ground. Oh, maybe just analyse things from the wind's perspective at that point, eh? Heads you win, tails I eat my hat?

Another place - second page - you said if you up the gradient of the treadmilll it gets to a point where it just hovers indefinitely. So we have still air in the room, we have a belt moving backwards past the wheels and slightly downwards as well, and we now add to that the force of gravity on the cart. And somehow you're telling me that the belt drives the wheels, thence the prop, enough to counter all the downward-backward forces into the system.

If you put it on a stationary slope, it would roll backwards. If you wafted it backwards in mid air in your hand, it would hardly resist with a noticable force. Yet PROPELLED backwards by a moving surface, it fails to just trundle off backwards with it, and provides enough resistance - is given enough power by that backward thrust itself! - to drive itself forwards, up a slope.

You're having a laugh. Cool brainteaser though.

 

[Modified]

And if you do that, analysed the system with respect to the belt, wind doing all the work, once the machine is at windspeed (assuming no losses) the wind, which you just said did all the work, isn't moving anymore with respect to the car, and thus has no effect on it.

As Thabiguy pointed out, the wind is still moving with respect to the "screw surface" of the prop. Imagine the prop is replaced by a screw and the wind is replaced by a ribbed belt that interfaces with the screw. The result will be a down belt faster than the belt vehicle. Maybe thinking about how that would work will help you to understand how the DWFTTW vehicle works. As the vehicle is pushed forward by the belt, the turning of the screw caused by that pushing (through gearing to the wheels) forces it to "screw forward" faster than the belt.

 

[ynot]

<ynot’s sceptic within>

Hmmmm . . .

I know that a wheeled cart powered by the worlds most efficient sail can’t go downwind faster than the wind because of the rolling resistance of the wheels.

I know that if gears, bearings and a zero pitched propeller are fitted to the cart the rolling resistance will be increased and the cart will go even slower with the wind.

I know that if a pitched propeller is fitted it will create even greater rolling resistance because the thrust it creates requires energy.

I can see no explanation as to how this thrust can be greater than, let alone be equal to, the rolling resistance it creates.

So why do I think such a cart can travel downwind faster than the wind?

</ynot’s sceptic within>

Think I had better stop this ridiculous flip-flopping and just say I don’t know, but lean more towards the conclusion that it doesn’t work than it does. When I think about it the main thing that induces me to think that it might work is the practical demonstrations provided by the treadmill videos. Although I can’t think of a good reason why the people involved would wish to do so, these tests could be very easily faked. There are also things about the testing that I'm not happy with. The only way to know for sure is to do my own testing. Unfortunately for the next 6 weeks I will be too busy with my business and travelling on holiday to make a cart and test it. If this subject still interests me then I will build a cart (or buy Spork’s) and test it the way I think it should be tested and put the results on Utube. I hope someone provides more credible proof or disproof before then.

 

[Michael C]

And if you do that, analysed the system with respect to the belt, wind doing all the work, once the machine is at windspeed (assuming no losses) the wind, which you just said did all the work, isn't moving anymore with respect to the car, and thus has no effect on it. Now you need to find some force again, but you've got stationary ground. Oh, maybe just analyse things from the wind's perspective at that point, eh? Heads you win, tails I eat my hat?

So according to you, if an object is stationary with respect to the air, the air can be having no effect on it? Or if it is stationary with respect to the ground, the ground can be having no effect on it?

 

[spork]

And if you do that, analysed the system with respect to the belt, wind doing all the work, once the machine is at windspeed (assuming no losses) the wind, which you just said did all the work, isn't moving anymore with respect to the car

No - but it is moving w.r.t. the swinging blades of the prop which create more than enough lift to propel the cart - clearly.

Heads you win, tails I eat my hat?

The bad news is this... if you have intellectual integrity you will end up eating your hat. The good news is that you might actually find it was worth it to come to understand such a clever little gizmo.

you said if you up the gradient of the treadmilll it gets to a point where it just hovers indefinitely. So we have still air in the room, we have a belt moving backwards past the wheels and slightly downwards as well, and we now add to that the force of gravity on the cart. And somehow you're telling me that the belt drives the wheels, thence the prop, enough to counter all the downward-backward forces into the system.

That's what I'm telling you. I know it sounds crazy. But I also know how it works and that it's absolutely true. The only thing that surprises me is that you won't allow us to explain to you how it works (by starting with a simpler vehicle).

Yet PROPELLED backwards by a moving surface, it fails to just trundle off backwards with it, and provides enough resistance - is given enough power by that backward thrust itself! - to drive itself forwards, up a slope.

You're having a laugh.

Believe me it's much more frustrating than it is funny that I can't convince people that this is real whether through analysis, video proof, or even direct physical proof since they won't drop $40 to build one for themselves.

I know that a wheeled cart powered by the worlds most efficient sail can’t go downwind faster than the wind because of the rolling resistance of the wheels.

In fact it can. Land yachts attain a downwind velocity component greater than the wind as an everyday affair. This is not even in contention. The trick is to come up with a clever way to do that same thing while going DIRECTLY downwind. For $40 you can do exactly that.

I can see no explanation as to how this thrust can be greater than, let alone be equal to, the rolling resistance it creates.

Then please allow us to explain using simplified examples.

Think I had better stop this ridiculous flip-flopping and just say I don’t know, but lean more towards the conclusion that it doesn’t work than it does.

But you have to ask, why would we build these carts, post these videos, debate this on internet forums, and describe how to build your own, only so we can be shown to be fakes. I can't imagine what upside there would be to faking this. We've invested a ridiculous amount of time into this silly thing only as some sort of perverse hobby (we love being insulted). Even the parts kit I've offered, I'm offering at my cost of parts - and I expect to put at least a couple hundred bucks worth of my own time into each one I send out.

There are also things about the testing that I'm not happy with.

I can hardly believe that you're not happy with the videos. But you seem to be willing to believe given the right evidence. So I'll tell you what... give me an EXACT script for the test you want to see and I'll do it. Don't leave anything out. Do you need to see a level? Do you need us to move the cart through the handle a few times to prove there's no string? Should I pan the camera to prove there's no fan? I know you've done it before, but indulge me. Tell me exactly what you want to see and tomorrow you will see just that.

 

[spork]

ETA: Spork, I tried to look up the L/D numbers for your prop but all the simulations seem to assume that the prop is moving through the air. Have you got a reference for these numbers or would it be possible for you to measure them in "still" air at the RPM of the prop on your cart?

We actually built a ridiculous dynamometer to take those measurements from our big cart (you can even see the plot in our video). But I haven't done so for the little guy. Let me see if I can figure out an easy way to do so.

 

[Dan O.]

A simple frame hanging by wires...



The wires carry electric current to the dc motor connected to the prop shaft. The frame will be pulled forward by the thrust of the prop and twisted by the drag/motor torque. Read the angles and convert to forces with a little trig.

 

[John Freestone]

Here is another down wind craft.


A simple weight and gearing on each vane axle causes the vane to make a 1/2 rotation for each full rotation of the main wheel. This causes the vanes to open to the wind when they are below the axis of the main wheel and close when they are above. Since the vanes below the axel are moving slower than the axle relative to the ground, the wind is still abel to push them forward even when the axle (and the average speed of the wheel) is moving somewhat faster than the wind.

Oh, this is priceless. If the vanes are positioned to catch the wind when below the axle and flop over to avoid it when above the axel, any wind would tend to push the bottom of the wheel, and tend to rotate it backwards against the wind. I don't know if such a device could progress up-wind, but it ain't going to get added thrust from the wind as it goes downwind, even if it was going downwind to start with. The speed of the vane at bottom being slower than the centre of the axel doesn't make any difference to the force applied to it by the wind, but in order to understand that, you'd probably have had to get the first bit right. When you build one of these, BTW, two wheels with the flopping vane thingies between them might be an idea. A unicycle could stay upright once it's rolling, but before it gets to that point it would have fallen over sideways, squashing the man next to it. There is also no need, in case you're wondering, to build one quite sooooooooooo large to test your hypothesis, but good luck.

No - but it [the wind] is moving w.r.t. the swinging blades of the prop which create more than enough lift to propel the cart - clearly.

No. Bootstrapping again. The air may possibly be moving past the blades of the prop in the sense you're suggesting - i.e. from back to front - because of their rotation, under certain circumstances, but their 'swinging' cannot create 'lift' off the air moving past them (in the sense of a turbine, i.e. gaining energy) and at the same time be acting as a driven air-screw, propelling the vehicle against the air resistance.

In fact it can. Land yachts attain a downwind velocity component greater than the wind as an everyday affair. This is not even in contention.

Oh yes it very much is.

The trick is to come up with a clever way to do that same thing while going DIRECTLY downwind.

This suggests that if you take the wind's direct force and reduce it by going at some angle to it, you are at an advantage, which reduces as you point directly downwind again. This is utter nonsense. I don't know about land yachting, but if we are discounting energy added to the system by a person rocking or swinging a vane, etc., the most efficient use of the wind power would be to have a perpendicular sail catching it full on and pointing downwind. Mechanical losses (considerable) mean that the wind will still be whistling past you from the rear at your full speed, and however you turn w r t the wind, or turn your sail w r t it, you can only reduce the efficient collection of that vector force.

Then please allow us to explain using simplified examples.

I am allowing you to explain any way you like. The only problem is that your explanations so far are contrary to the laws of physics.

But you have to ask, why would we build these carts, post these videos, debate this on internet forums, and describe how to build your own, only so we can be shown to be fakes. I can't imagine what upside there would be to faking this. We've invested a ridiculous amount of time into this silly thing only as some sort of perverse hobby (we love being insulted). Even the parts kit I've offered, I'm offering at my cost of parts - and I expect to put at least a couple hundred bucks worth of my own time into each one I send out.

I don't have to ask myself that. People do the weirdest things. I imagine that eventually when enough people have been conned into making their own, and you've had a good laugh at all the ridiculous things people come up with on internet forums to try to get round Newton's laws, you'll probably go "Yeah, it was a great practical joke, wasn't it? You guys!"

I can hardly believe that you're not happy with the videos. But you seem to be willing to believe given the right evidence. So I'll tell you what... give me an EXACT script for the test you want to see and I'll do it. Don't leave anything out. Do you need to see a level? Do you need us to move the cart through the handle a few times to prove there's no string? Should I pan the camera to prove there's no fan? I know you've done it before, but indulge me. Tell me exactly what you want to see and tomorrow you will see just that.

I don't consider video evidence as giving proof. It's possible to fake just about anything. How hard is it to make a little tube of clear resin with a bubble in the middle and fit it in place of the window in a level? Then you can put a treadmill at any angle you like and, if you pay enough attention to the rest of the room details, the eye will imagine it's level. I'm not saying you did that, but you could have. You can pass the vehicle round a fixed pole, taking the extremely fine pulling cord attached to its nose with it, the one you use to slowly pull your magic cart up the treadmill before pushing it back with your spork. I'm not saying you did that, but you could have. (Actually, it's one of the most obvious solutions.)

I've seen videos of people levitating, while their friends move round them and pass things under them. I still don't believe in levitation.

 

[John Freestone]

If the only force was friction why does it stop working when the propeller is disconnected. In fact any amount of friction reduces it's ability to climb the treadmill so claiming the only force is friction doesn't wash.
http://www.youtube.com/watch?v=LMgDvC5lqsY

Just supposing in this video, where we are not shown what is to the left (equivalent downwind) of the treadmill, there is a ruddy great fan. This would explain:

a) the motion of the vehicle in normal test mode, propelling itself, we are told, faster than the progress of a belt under its wheels, driven only by that belt under its wheels - it could, in fact, be being pushed via air blown left to right, turning the prop (actually a turbine), this giving the required extra energy Newton didn't think of,

b) the motion of the vehicle backward, as would be expected, when its turbine drive is disconnected, and

c) the apparent turning of the prop from a standstill at about 0:50, after it's second pass round the frame of the treadmill. What seems to happen is that when spork is holding it by its gear joint, as he does most of the time (oddly), the prop comes to a rest. Then, on that second pass, he momentarily has to change hands, and grabs the machine by its frame between the wheels. At that point, with no great forward motion of the machine in his hands, the prop seems to begin turning of its own free will. Spork holds the machine again immediately by its gear, and it stops again. He also seems always to place it on the treadmill while holding it at this position, perhaps because if he didn't apply a little friction there, we would see the prop spinning without the wheels being in contact with the belt, and, while he manages to get away with convincing some people that the system can gain energy from nowhere while it's going, no-one will believe it sucks power straight out of motionless air.

So, ok spork, if you want to get some way nearer to a decent test video, we need you to pan both ways, all round the room preferably, to see the whole rig. You need to hold the machine by its frame sometimes as you hover it over the treadmill. It might also help if, having let go, you could do a little jig or spin on your heels - that way we're more confident that you're not holding a piece of thread attached to the machine to make it track 'uptread'.

However, nothing will really convince me except making my own, and I ain't gonna do that, now am I? I'd like to know if anyone here has taken you up on the idea, who was a sceptic, built one, and now says well blow me down with a wind-turbine, I'm converted.

Let's take another think about this from the physics again. You say that there is some kind of equilibrium state - if it goes too slowly, it's 'obviously' gaining energy until it speeds up, which is where the stopper is needed at the front. But you don't - presumably - claim that it would continue to accelerate indefinitely if not stopped, so it would also get to a terminal velocity. If somehow propelled faster than that, the system would tend to return to its equilibrium again.

There's nothing odd about that and, taking the vids at face value, that fits. However...

Now, imagine it's just going a little faster than that equilibrium, for whatever reason - maybe the operator gave it an accidental push. Right, so we can recognise what happens. The various inefficiencies in the system cause it to slow down. Slowing down, however, causes its wheels to be moving slower w.r.t. the treadmill (if you push it against the tread, the wheels spin faster, let it roll backwards, wheels slow down w.r.t. the treadmill's steady speed). Now, that backward acceleration of the cart must reduce the power derived from the treadmill, which can only translate into less power output at the propeller. Less power output at the propeller can only cause the cart to be pushing forwards against the air and up-tread a little less. If it pushes forwards up-tread with a little less force, the relative speed of wheels over tread is further reduced, which is supposedly all that's powering the propeller, so the propeller will slow a little more, which will.........I think we can all see where that's going.

As I put it much more simply before, to cause that cart to remain at rest in a system where the only input force is right to left....well, the sentence can't be completed without contradicting itself. It would remain at rest if there were no friction at the wheels/tread interface. You have disproved Newtonian physics. Furthermore, it's not supposed to be staying at rest, but moving up-tread. You have simulated a surface with negative friction, using a few bits from a hardware store. All our energy problems are over.

 

[ThinAirDesigns]

However, nothing will really convince me except making my own, and I ain't gonna do that, now am I? I'd like to know if anyone here has taken you up on the idea, who was a sceptic, built one, and now says well blow me down with a wind-turbine, I'm converted.

http://www.youtube.com/watch?v=MfZt19F-OA4

Send a private message to the maker of this video. He called us every name in the book. He made several well documented but failed attempts. The conflict went on for close to 3 years.

We succeeded and posted our video and according to him he didn't sleep for about 2 days while he built one and absolutely couldn't believe it.

The cart he came up with during that 24 hours was so simple we turned around copied it.

JB

 

[John Freestone]

As Thabiguy pointed out, the wind is still moving with respect to the "screw surface" of the prop. Imagine the prop is replaced by a screw and the wind is replaced by a ribbed belt that interfaces with the screw. The result will be a down belt faster than the belt vehicle. Maybe thinking about how that would work will help you to understand how the DWFTTW vehicle works. As the vehicle is pushed forward by the belt, the turning of the screw caused by that pushing (through gearing to the wheels) forces it to "screw forward" faster than the belt.

I don't think so. You seem to be making the same claim of getting something for nothing. I can get a rough picture of this in my head, and haven't drawn it or anything, but let's describe the essential features of your idea in more detail. The belt is pushed past the screw, forcing the screw to turn. However, the screw actually only turns because it is mounted somewhere. If it were mounted on a motionless block, it would turn, the belt would pass it, and we've nothing very interesting going on. Allow it to screw, however, by some means along another track, screw or any kind of gearing system you choose, so that it moves in the direction the belt is trying to push it, and we now have something a little closer to analogous. However, you are suggesting that the screw, representing the 'vehicle' can utilize such a gear system to screw itself along the belt. This is indeed what is suggested in the analogue, that the wind pushes the prop as a kind of bluff, driving the mechanism, which translates back to an air-screw pushing against the wind that cause it to do so.

So, thinking about these simple screws, if you imagine the vehicle-screw forcing itself forward with respect to the belt because it is turning, you get the impression that it can move faster than the belt. But whatever force it applies to the belt backwards to drive itself forwards faster than the belt can only have originated in the force applied to the screw by the belt in the first place. You might as well try to push a ladder up a wall from the floor while climbing the ladder.

So according to you, if an object is stationary with respect to the air, the air can be having no effect on it? Or if it is stationary with respect to the ground, the ground can be having no effect on it?

They're having effects on each other of all sorts, but in terms of the relevant mechanics, that is absolutely bog standard. Any engineer should be able to confirm this. You can't gain momentum from a null relative motion, no matter what's happening relative to other things. Does a little plastic windmill on a stick rotate if you hold it in the perfectly still air? If you're going a hundred miles an hour in a car and do the same, in the same relatively stationary air inside the car, does it turn? No. Stick it out the window, hey presto, it turns.

 

[ThinAirDesigns]

Spork:

In fact it can. Land yachts attain a downwind velocity component greater than the wind as an everyday affair. This is not even in contention.

John:

Oh yes it very much is.

John, then this discussion is really pointless until you educate yourself on the above point.

On the NALSA.org website (the NALSA is the sanctioning body for landyacht racing in the US) you can dig around and find much to confirm the validity of sporks point. But better yet, go ask them yourselves -- I did:

http://sports.groups.yahoo.com/group/2nalsa/message/161

Ice-boats and land yachts regularly achieve VMGs of 3x+ the down wind speed.

Unless you can come to accept the reality of the ice-boat breaking *your* laws of physics, chatting about the cart is just a waste of time.

Do the research.

 

[Thabiguy]

I am allowing you to explain any way you like. The only problem is that your explanations so far are contrary to the laws of physics.

All right. Okay. Let's give it a try.

Forget about the propeller-based device for now. Just forget about it.

Look at this device (illustration by Myriad):

Using the laws of physics, answer these questions:

When you pull on the upper chain towards the right, will it move? Will the wheel move? If the chain moves, and the wheel moves, and the chain's velocity towards the right is v, what is the velocity of the wheel?

Note: when answering these question, please do not refer to the propeller-based device. Refer only to this one.

 

[sol invictus]

Oh yes it very much is.

I posted a link a while back to some GPS data recorded by an iceboat during a race, which shows the boat exceeding the speed of the wind by factors of 5 and more. Was that a fake as well?

You've obviously never windsurfed or been on a fast sailboat - it's very easy to exceed the speed of the wind across a broad range of reaches.

I am allowing you to explain any way you like. The only problem is that your explanations so far are contrary to the laws of physics.

Why don't you tell us precisely which laws of physics you think are being violated? Be specific, please - "Newton's laws" doesn't cut it.

It can't be conservation of energy, unless you think wind turbines violate that too.

It can't be conservation of momentum, unless you keep track of the momentum of the earth and the air as well as the cart.

It can't be conservation of force, because there is no such thing.

It can't be F=ma, because people have posted force-balance analyses which show clearly that the cart can accelerate down wind starting from wind speed (the only thing that can possibly prevent it is friction, which can be minimized).

So..... what law of physics is it, John?

 

[spork]

So..... what law of physics is it, John?

I've been here before. The answer is EVERY law of physics.