DDWFTTW Turntable Test: 5 Min Video - Is It Conclusive?

[zoobyshoe]

OK, that was a theoretical extreme. How about an iceboat downwind component during a downwind tack? Although more efficient than a DDWFTTW cart, perhaps it will demonstrate the possibility. A link to a .pdf file from an ice boat web site:

http://www.nalsa.org/Articles/Cetus/Iceboat Sailing Performance-Cetus.pdf

There's are a couple of diagrams from a real iceboat run. In the second one, "downwind angles: Skeeter", the wind speed is 18 mph, and the ice boat's heading is 30 degrees offset from true downwind. The apparent crosswind speed is 18 mph x sin(30) = 9 mph, regardless of the iceboats speed. In this case, the iceboat can achieve an apparent headwind speed of 54.4 mph with an apparent crosswind of 9 mph. This tranlates into a ground speed of 70 mph for the ice boat, and an apparent total wind of 55.15 mph (shown as 55 mph in the diagram, I included the .15 so the heading angle offset was 30 degrees). The net downwind speed is 70 mph x cos(30) = 60.6 mph, over 3 times the speed of the wind. Using my numbers (55.15 mph), and a 30 degree heading, I calculate a Beta of 9.4 degress (atan(9/54.4)) about 6:1 as opposed to the 8 (about 7:1) degress shown on the diagram, I'm not sure if this was a mistake or due to rounding errors.

This is dazzling at first, and can easily lure someone into thinking there's a way to translate it to ddwfttw, but the skeeter, itself cannot do it, which should give you pause. The fact we can sail 45 degrees off the wind if we exchange square sails for sloop sails suggests that an even cleverer sail might be able to go directly into the wind. There's that thing where if you stand a yardstick up vertically and let it fall the tip will have accelerated faster than g when it hits the deck, which is popularly known as "Freefall Faster Than g". It might suggest that there's also probably a way to freefall straight down faster than g.

The most convincing argument will be a proof: make an actual cart and send it down wind outdoors. Clock it and clock the windspeed. It should be easier to make an actual cart than the whole turntable thing swerda made.

 

[zoobyshoe]

There is no physical law that tells me that I need a certain amount of mass to have a certain sail. I don't break any conservation of energy or momentum by having a 10 gram sail and mast which is strong enough to do so. I won't find any actual material that does so in the current state of technology, but I don't break any laws of classical mechanics by having a very high material strength to mass ratio.

What people here are claiming is that downwind faster than the wind is breaking some fundamental laws of classical mechanics. It doesn't. In order to show that it doesn't, I'm allowed to use any imaginary system that respects classical mechanics.

I'm trying to disprove a theorem. The theorem is: *classical mechanics* forbids in principle to go DWFTTW. Well, if I can find ONE counter example, that is, something that respects entirely all the laws of classical mechanics, and nevertheless goes DWFTTW, then I have disproven the theorem.

That's what I did, already a few times.

The theorem "DWFTTW is prohibited by classical mechanics" is an erroneous theorem.

I'm not proposing any theorems. I have a big problem with the DW etc. notion because of "Power available from the wind is proportional to V^3" .

The OP presents an actual physical demonstration (of something) so I assumed the idea was that this had to be proven to be practically possible. Likewise, Jeff Reid seems to be getting most of his inspiration from actual ice boats, which supports my assumption. To the best of my knowledge you are the only one who is perfectly satisfied with a gedanken version and nothing more concrete.

 

[schroder]

agreed.

I just posted two links to videos showing cart start up in a true wind.

http://www.youtube.com/watch?v=QTAd891IpRs&fmt=18

http://www.youtube.com/watch?v=kWSan2CMgos&fmt=18

In the second segement of the second video a strong gust does initially turn the the prop as a turbine, causing the wheels to be driven backwards and sliding as the cart moves forward, but the wheels regain traction and starting turning the prop in the correct direction.

I see what your concern is, that the prop could act as a turbine at sub wind speeds, but these DDWFTTW carts are using props with a low pitch factor. The geometric advance of the prop per revolution is small, much smaller than the circumference of the driven / driving wheels. The prop in this case has a 12" diameter and a 6" per revolution pitch. That means the prop tips travel 37.7" perpendicular to the wind for every 6" inches the prop moves forward. That's the equivilant of an AOA of around 9 degrees at the tips, so the turbine effect from the tailwind at sub-wind speeds is small. In this case the advance ratio is 6" / 10.5" (prop pitch / wheel circumference), providing the wheels with enough "leverage" to prevent a turbine reaction from the prop, unless the wheels slide as in the case of the gusting wind in the second video. The startup videos are evidence of how the carts behave in a true wind.

I have looked at the videos, more than once! In the second (outdoor video) you posted, it is clear to see that the first initial gust of wind, at 0:08 seconds, does in fact turn the prop CCW as a turbine, and the wheels are dragging on the ground. (Because of wrong gearing) At 0:13 seconds, we are treated to a prop suddenly reversing in direction, driving the wheels the right way so the cart can in fact move down wind. Is it moving faster than the wind? I rather doubt that, as at 0:14 seconds, a piece of scrap paper, being blown by the wind, absolutely trashes the cart, as it blows past at a much higher velocity. To top it off, a man who was standing at the start line, takes off at a casual jog after the cart has a considerable head start, and easily catches up to it. Not very impressive! But getting back to your point that the force on the wheels is greater than the force on the prop, so the wheels overcome the initial direction of the prop and cause it to reverse direction. I don’t buy that for one second. The cart is quite aerodynamic, it offers very little in the way of blunt object wind resistance. The propeller is by far and away the biggest area presented to the wind. Once the wind starts to turn the propeller in accordance with its fixed pitch, and the wheels start dragging on the ground, there is only one way I can see which will allow the prop to reverse and the wheels start running the right way: that is a differential gear, which senses that forward motion is impossible and so slips the prop rotation into mode 2, which is to change the direction of gearing. If that is what is happening, this amounts to a hoax, nothing more, nothing less! I do not intend to spend the rest of my life busting this hoax, but I think you should realize that I am just an engineer (civils and electrical) and a member of New York Academy of Science. There are other people far more qualified than myself who are now expressing an interest in this, and in those forums which are promoting this. My advice is to let swerdna run some more tests, as I think he is genuinely interested in knowing the truth, and he is not trying to hoax anyone, and let the chips fall where they may. Is that acceptable to everybody?

 

[zoobyshoe]

True, but this doesn't mean the limit is the speed of the wind. The air flow through the propeller is accelerated upwind...

I don't think so. The airflow goes downwind through the prop transferring energy to the cart, but only so long as its speed relative to the cart affords it the power to do so. The more it succeeds the less it is able to build on its success: diminishing returns. Friction never sleeps.

 

[zoobyshoe]

Hey Jeff, here's your boat!

 

[schroder]

Hey Jeff, here's your boat!

I like that, although I would be happier with a pair of oars myself. Hopefully, no one is claiming that can go faster than the wind! But it can be useful as a fun vehicle.

 

[vanesch]

I'm not proposing any theorems. I have a big problem with the DW etc. notion because of "Power available from the wind is proportional to V^3" .

The OP presents an actual physical demonstration (of something) so I assumed the idea was that this had to be proven to be practically possible. Likewise, Jeff Reid seems to be getting most of his inspiration from actual ice boats, which supports my assumption. To the best of my knowledge you are the only one who is perfectly satisfied with a gedanken version and nothing more concrete.

Why is this demonstration so vehemently attacked ? After all, it does prove a DWFTTW case, with only a few minor points of discussion: the fact that it is on a disk with a radius which is not so much larger than the size of the installation and so on might make one think that locally, the reference frame attached to the turntable is not entirely an inertial frame (because of the rotation). This is the ONLY problem with the OP's experiment. If the reference frame of the disk can be seen as an inertial frame, then you put yourself in that frame, the turntable is at rest, the air in the room is flowing in at the opposite speed of the turntable (speed in the lab frame, because in our reference frame, it is at rest), and the cart is running backward faster than the wind it receives. So to me, that's DWFTTW in the reference frame attached to the turntable. It is not a perfect inertial frame because of the smallness of the radius of the disk. So would it work too on a bigger turntable ? I would think so but that's the only question.

Now, why is this simple experiment with a clear conclusion put in doubt ? Because people here think it is IN PRINCIPLE impossible to go DWFTTW. Some say it are "over unity devices", others say it is against conservation of momentum and all that. If that were true, then it would be a simple THEOREM in classical mechanics that there is no possibility of having a DWFTTW device. It is on this supposed theorem that people attack the rather obvious demonstration. If they would not be a priori convinced that DWFTTW were impossible, this would be just a fun demonstration of something that might not be intuitively evident at first sight, but no more surprising than to find that you can wind up a wire around a wheel by pulling on the wire (see my post with two pictures attached to it).
So the real problem here is that people ASSUME that there is some theorem in classical mechanics that forbids DWFTTW. Well, it is then sufficient to disprove this so-called theorem, and for that, a gedanken experiment is sufficient (it is also sufficient to see no proof emerge by those claiming nevertheless that DWFTTW is impossible...).

A theorem for which no proof is advanced, and for which there are "gedanken experiments" that serve as counter example is no theorem. In other words, NOTHING in classical mechanics forbids IN PRINCIPLE DWFTTW. And once you're there, the original objections to the demonstration are moot.

Because if the demonstration is genuine, then it is hard to motivate why this is NOT a practical demonstration of DWFTTW, unless we're not allowed anymore to assume that physics is independent of the choice of inertial frame.

So, in conclusion: we have a nice demonstration of an effect in the lab (true, with the small caveat that the radius of the turntable is maybe not big enough), and a disproof of any theorem that might forbid such an effect.

So where are the grounds to claim that the demonstration is not possible and that the thing "would not work" in a "real wind situation" ?

 

[vanesch]

I don't think so. The airflow goes downwind through the prop transferring energy to the cart, but only so long as its speed relative to the cart affords it the power to do so. The more it succeeds the less it is able to build on its success: diminishing returns. Friction never sleeps.

But at wind speed, you have power available on the axle of the wheels ! You can use that in principle to make a prop turn and get you faster. The energy goes from the wheels to the prop. The slightest bit of power that you can extract from the axle and put into the air (which is now "standing still") will get you move faster than the wind.

But this is not an over-unity device. The reason is that taking a small amount of power from the wheels will make them tend to spin less slow by a smaller amount than the increase in velocity you can get by the wind. The reason for that is that the kinetic energy goes as v^2.

As such, wrt the ground, at a velocity v_wind, if you take away energy E, you would tend to go from 1/2 m (v_wind)^2 to 1/2 m (v_wind)^2 - E. You would hence tend to slow down from v_wind to sqrt(v_wind^2 - 2 E / m), which is approximately E/ v_wind m.

However, wrt to the air (which is stationary), you go from 0 to E. So here you tend to increase your velocity by sqrt(2 E / m). For small E, this is a strong increase (the derivative of sqrt(x) at the origin is infinite). So for small enough E, this is always bigger than E/v_wind m. So taking some axle energy and putting it into any air acceleration will always win you some velocity for small enough losses.

The reason why this is not an over-unity device is because you have the air at 0 speed while the ground is NOT at zero speed, and it is this difference which makes that energy borrowed from the ground "pays off" to the air.
A self-propelled "over unity" device doesn't work, because there is no speed difference, so both energy functions start off at the same slope. There can only be losses. There's nothing to be gained from taking energy from the axle to put it in the air. Both have the same kinetic energy formula with the same origin.

 

[schroder]

Why is this demonstration so vehemently attacked ? After all, it does prove a DWFTTW case, with only a few minor points of discussion: the fact that it is on a disk with a radius which is not so much larger than the size of the installation and so on might make one think that locally, the reference frame attached to the turntable is not entirely an inertial frame (because of the rotation). This is the ONLY problem with the OP's experiment. If the reference frame of the disk can be seen as an inertial frame, then you put yourself in that frame, the turntable is at rest, the air in the room is flowing in at the opposite speed of the turntable (speed in the lab frame, because in our reference frame, it is at rest), and the cart is running backward faster than the wind it receives. So to me, that's DWFTTW in the reference frame attached to the turntable. It is not a perfect inertial frame because of the smallness of the radius of the disk. So would it work too on a bigger turntable ? I would think so but that's the only question.



So where are the grounds to claim that the demonstration is not possible and that the thing "would not work" in a "real wind situation" ?

I have already presented my detailed reason why this is NOT a valid inertial reference frame. Either you were missed it or simply chose to ignore it. Let me begin by an example: Place a sailboat in a frame in which the water is calm but the wind is blowing. The sail is up, and the skiff is sailing downwind. Now place the exact same sailboat in an equivalent reference frame, the air is calm, but the water has a current which is flowing in the opposite direction the wind was blowing in reference A. This causes a relative wind to blow which is indistinguishable in frame B from the wind in frame A. The sailboat sails downwind exactly as in frame A. The two frames are equivocal. I go through this exercise not to insult your intelligence, but just to be sure we are on the same page here.
OK. Now we take this cart, just a wheel with a propeller and hook it up as in the video and run it exactly as we have seen. The turntable spins CW, the cart gets dragged backwards for a short while due to inertia, static resistance but soon enough the apparent wind working against that wide yardarm, as well as the cart and propeller, slows the movement of the cart relative to the movement of the turntable. This slowing causes a relative difference in velocity as seen by the drive wheel, which spins up and via the cable also spins the propeller. The direction of spin and pitch of the propeller is such so that it acts as a true propeller, not a mill, and it propels the cart to move counter to the spin of the table. The cart can be seen advancing against the table. Now, your interpretation is that this is an equivalent reference frame to a stationary table and a true wind blowing on the back of the cart. You also interpret this as the cart going faster than the wind, since it is advancing against the table. Here is where you are wrong: This would ONLY be an equivalent reference frame if the cart were to move in exactly the same direction and at the same velocity, if it were driven NOT by the moving table, but instead by an actual wind blowing on the cart as it stands on a stationary table! I have already shown, and Jeff agrees, that if a wind were to blow on the propeller, with the cart stationary on the table, the propeller will act as a turbine, turning the opposite way, turning the wheels the opposite way, and the cart will try to work AGAINST the wind, not go down wind! Do you still consider the two frames to be equivalent? Under the same relative environmental conditions, the cart will behave two different ways! That is NOT an equivalent reference frame by any means! As I have said, countless times, you cannot test a cart which is configured for upwind motion and claim that it proves down wind performance! I have showed you how to set up the cart so that it is a true down wind cart; simply remove the drive cable from one side of the wheel and attach it on the other side that is all that is required. Now, when you run the test, it will be a TRUE equivocal reference frame with a cart in the wind. What you will find is that the cart on the turntable will run backwards with the table until the wind resistance turns the mill as a turbine, which turns the wheels, and it will indeed go down wind, but it will NEVER exceed the table velocity. This will PROVE the DDWFTTFW is impossible. You can take that same cart, same configuration, and place a fan behind it and it will go downwind, something the original configuration could NOT do! Can you now understand the importance of not mixing and matching reference frames? Test the DW cart on the turntable configured as it would be to go DW. Test the UP wind cart configured on the turn table in the same configuration it will be when going up wind. Please do not mix and match! Is there no one here who understands this?

 

[zoobyshoe]

Why is this demonstration so vehemently attacked ?

I haven't attacked it, vehemently or otherwise. I have, pretty calmly, expressed skepticism about it.

After all, it does prove a DWFTTW case, with only a few minor points of discussion: the fact that it is on a disk with a radius which is not so much larger than the size of the installation and so on might make one think that locally, the reference frame attached to the turntable is not entirely an inertial frame (because of the rotation). This is the ONLY problem with the OP's experiment. If the reference frame of the disk can be seen as an inertial frame, then you put yourself in that frame, the turntable is at rest, the air in the room is flowing in at the opposite speed of the turntable (speed in the lab frame, because in our reference frame, it is at rest), and the cart is running backward faster than the wind it receives. So to me, that's DWFTTW in the reference frame attached to the turntable. It is not a perfect inertial frame because of the smallness of the radius of the disk. So would it work too on a bigger turntable ? I would think so but that's the only question.

Now, why is this simple experiment with a clear conclusion put in doubt ? Because people here think it is IN PRINCIPLE impossible to go DWFTTW. Some say it are "over unity devices", others say it is against conservation of momentum and all that. If that were true, then it would be a simple THEOREM in classical mechanics that there is no possibility of having a DWFTTW device. It is on this supposed theorem that people attack the rather obvious demonstration. If they would not be a priori convinced that DWFTTW were impossible, this would be just a fun demonstration of something that might not be intuitively evident at first sight, but no more surprising than to find that you can wind up a wire around a wheel by pulling on the wire (see my post with two pictures attached to it).
So the real problem here is that people ASSUME that there is some theorem in classical mechanics that forbids DWFTTW. Well, it is then sufficient to disprove this so-called theorem, and for that, a gedanken experiment is sufficient (it is also sufficient to see no proof emerge by those claiming nevertheless that DWFTTW is impossible...).

A theorem for which no proof is advanced, and for which there are "gedanken experiments" that serve as counter example is no theorem. In other words, NOTHING in classical mechanics forbids IN PRINCIPLE DWFTTW. And once you're there, the original objections to the demonstration are moot.

Because if the demonstration is genuine, then it is hard to motivate why this is NOT a practical demonstration of DWFTTW, unless we're not allowed anymore to assume that physics is independent of the choice of inertial frame.

So, in conclusion: we have a nice demonstration of an effect in the lab (true, with the small caveat that the radius of the turntable is maybe not big enough), and a disproof of any theorem that might forbid such an effect.

So where are the grounds to claim that the demonstration is not possible and that the thing "would not work" in a "real wind situation" ?

I am not claiming it is not possible, but I admit to having a "real problem" with it, which I have described already.

Jeff has linked to an outdoor demonstration in real wind in which, I'll admit, the cart looked pretty zippy, so if it bothers you that I don't share your confidence in it, then just look forward to the possibility of saying "I TOLD you so!"

 

[vanesch]

I have already presented my detailed reason why this is NOT a valid inertial reference frame. Either you were missed it or simply chose to ignore it. Let me begin by an example: Place a sailboat in a frame in which the water is calm but the wind is blowing. The sail is up, and the skiff is sailing downwind. Now place the exact same sailboat in an equivalent reference frame, the air is calm, but the water has a current which is flowing in the opposite direction the wind was blowing in reference A. This causes a relative wind to blow which is indistinguishable in frame B from the wind in frame A. The sailboat sails downwind exactly as in frame A. The two frames are equivocal. I go through this exercise not to insult your intelligence, but just to be sure we are on the same page here.

We are.

OK. Now we take this cart, just a wheel with a propeller and hook it up as in the video and run it exactly as we have seen. The turntable spins CW, the cart gets dragged backwards for a short while due to inertia, static resistance but soon enough the apparent wind working against that wide yardarm, as well as the cart and propeller, slows the movement of the cart relative to the movement of the turntable. This slowing causes a relative difference in velocity as seen by the drive wheel, which spins up and via the cable also spins the propeller.

Yes.

The direction of spin and pitch of the propeller is such so that it acts as a true propeller, not a mill, and it propels the cart to move counter to the spin of the table. The cart can be seen advancing against the table. Now, your interpretation is that this is an equivalent reference frame to a stationary table and a true wind blowing on the back of the cart.

Yes.

You also interpret this as the cart going faster than the wind, since it is advancing against the table.

Yes.

Here is where you are wrong: This would ONLY be an equivalent reference frame if the cart were to move in exactly the same direction and at the same velocity, if it were driven NOT by the moving table, but instead by an actual wind blowing on the cart as it stands on a stationary table!

But where is the difference if you look upon this from the reference of the turning table ?

In what way can you say that the table is "really turning" and the air is "really stationary", and not that the table is actually standing still and the air is moving ? This is just a change of reference frame, no ?

(there IS a small difference, and that is the fact that the reference frame of the table also has a rotation which it shouldn't, as an inertial frame. But that can be made smaller with a larger turning table).

I have already shown, and Jeff agrees, that if a wind were to blow on the propeller, with the cart stationary on the table, the propeller will act as a turbine, turning the opposite way, turning the wheels the opposite way, and the cart will try to work AGAINST the wind, not go down wind!

Well, that's wrong. It will of course move with the wind in the beginning, because of the drag of the wind on the system (and the arm which acts as a sail). The propeller always acts as a propeller and not as a turbine. Because if that where the case, the cart on the turntable would speed FORWARD faster than the table and not run backwards. How would you explain that the cart is not running forward on the table, but would so when solicited with an external wind ? Again, it is a transformation of reference frames.

Do you still consider the two frames to be equivalent? Under the same relative environmental conditions, the cart will behave two different ways! That is NOT an equivalent reference frame by any means!

This is because you are wrong with your prediction of how it would behave of course.

As I have said, countless times, you cannot test a cart which is configured for upwind motion and claim that it proves down wind performance!

What is an "upwind configuration" ? If it runs downwinds, it will make the propeller *increase* that motion. If it runs upwind, it will make the propeller increase *that* motion. There could very well be TWO solutions to the equation of motion, depending on the initial conditions. Only, the upwind solution has not been demonstrated.

I have showed you how to set up the cart so that it is a true down wind cart; simply remove the drive cable from one side of the wheel and attach it on the other side that is all that is required.

No, if you do that, you have changed the "gear ratio" and hence you will change the motion.
That is not equivalent. It is as if you changed the gear ratio from p = 1/2 to p = -1/2 in my example. You don't get the same motions.

Now, when you run the test, it will be a TRUE equivocal reference frame with a cart in the wind. What you will find is that the cart on the turntable will run backwards with the table until the wind resistance turns the mill as a turbine, which turns the wheels, and it will indeed go down wind, but it will NEVER exceed the table velocity.

This is correct, but the two are not identical physical situations. Frame-independent quantities (such as the gear ratio) which are the same in every reference frame are now different. In order to have an equivalent frame, you should just apply a uniform velocity vector, and all the rest equal (for a galilean transformation). That's exactly what happens when you go from the turntable to the windtunnel (up to the small rotational motion).

This will PROVE the DDWFTTFW is impossible. Yodu can take that same cart, same configuration, and place a fan behind it and it will go downwind, something the original configuration could NOT do!

It will of course ALSO go downwind on the turntable, but not as much, because in order to act as a "turbine" in the downwind, it actually acts as a propeller making it move slightly with the turning table, and not against it, as was the case with the original cart (before changing the sign in the gearing ratio).

Can you now understand the importance of not mixing and matching reference frames? Test the DW cart on the turntable configured as it would be to go DW. Test the UP wind cart configured on the turn table in the same configuration it will be when going up wind. Please do not mix and match! Is there no one here who understands this?

I think it is you who do not seem to see that equivalent reference frames demand that you just apply a velocity transformation WITHOUT changing frame-independent quantities such as the sign of the gear ratio.

All that comes about because you make a wrong gedanken experiment of what the cart of the original poster WOULD do (according to you) when exposed in a wind tunnel.

You don't change the sails of your boat either when you do the equivalent frame transformation in the sea current versus wind case, do you ?

This is really very similar to the case of the winding of a wire on a wheel while you PULL on the wire. Only because of airodynamics, things are less evident.

 

[zoobyshoe]

But at wind speed, you have power available on the axle of the wheels ! You can use that in principle to make a prop turn and get you faster. The energy goes from the wheels to the prop. The slightest bit of power that you can extract from the axle and put into the air (which is now "standing still") will get you move faster than the wind.

"Friction never sleeps" means that I don't see how you will ever get up to wind speed as long as there is any friction in the cart's mechanical components. Going back to the 20mph wind; if the cart makes it to 19 mph, then the wind speed becomes 1 mph, which has 1/8000 the power of the original 20mph wind to add to the cart. I'm not sure a toy propeller will even freewheel in a 1 mph wind.

When you say there is power available on the axle, are you referring to stored flywheel power?

Let's say you make it to wind speed and have some little bit of energy. The prop is turning in the wrong direction to produce forward thrust into the head wind. Once it stops being driven by the wind its action will be to try to thrust the cart backward while continuing to turn the wheels forward. What's your solution to this?

 

[M Grandin]

The reality of this I thought was cleared up since long in this forum, both by video verifications and theoretical explanations.

This is not a new Einsteinian theory demanding abstract inertial frames
to explain - it is just a gearbox between two media, ground and air, with different velocities. By gearing this gearbox suitably, this difference in speed of medias could give this gearbox (at least theoretically) any speed in any direction. It is just an engineering task - where of course every specific solution has its practical limitations.

The power from differences of speeds of surrounding media can be extracted rather independently of gearbox`s (=vehicle`s) own speed. As maybe some pointed out
earlier. This is egineering, not abstract difficult comprehensible science.

 

[pallidin]

I agree. There is nothing particulary odd about this.
For example, it should not be surprising that a 10/lb constant force at 10/mph can be geared to have a resultant ground contact 5/lb force at 20/mph, minus losses of course.

 

[swerdna]

In relation to my original question can I assume the following . . .

Schroder and Zoobyshoe think DDWFTTW is impossible and not is not demonstrated by my turntable demonstrations and other demonstrations.

Jeff Reid, Vanesch and Phrak think DDWFTTW is possible and not is demonstrated by my turntable demonstrations and other demonstrations.

Is this correct?

 

[schroder]

But where is the difference if you look upon this from the reference of the turning table ?

In what way can you say that the table is "really turning" and the air is "really stationary", and not that the table is actually standing still and the air is moving ? This is just a change of reference frame, no ?

(there IS a small difference, and that is the fact that the reference frame of the table also has a rotation which it shouldn't, as an inertial frame. But that can be made smaller with a larger turning table).




Well, that's wrong. It will of course move with the wind in the beginning, because of the drag of the wind on the system (and the arm which acts as a sail). The propeller always acts as a propeller and not as a turbine. Because if that where the case, the cart on the turntable would speed FORWARD faster than the table and not run backwards. How would you explain that the cart is not running forward on the table, but would so when solicited with an external wind ? Again, it is a transformation of reference frames.



This is because you are wrong with your prediction of how it would behave of course.

What is an "upwind configuration" ? If it runs downwinds, it will make the propeller *increase* that motion. If it runs upwind, it will make the propeller increase *that* motion. There could very well be TWO solutions to the equation of motion, depending on the initial conditions. Only, the upwind solution has not been demonstrated.



No, if you do that, you have changed the "gear ratio" and hence you will change the motion.
That is not equivalent. It is as if you changed the gear ratio from p = 1/2 to p = -1/2 in my example. You don't get the same motions.




This is correct, but the two are not identical physical situations. Frame-independent quantities (such as the gear ratio) which are the same in every reference frame are now different. In order to have an equivalent frame, you should just apply a uniform velocity vector, and all the rest equal (for a galilean transformation). That's exactly what happens when you go from the turntable to the windtunnel (up to the small rotational motion).



It will of course ALSO go downwind on the turntable, but not as much, because in order to act as a "turbine" in the downwind, it actually acts as a propeller making it move slightly with the turning table, and not against it, as was the case with the original cart (before changing the sign in the gearing ratio).



I think it is you who do not seem to see that equivalent reference frames demand that you just apply a velocity transformation WITHOUT changing frame-independent quantities such as the sign of the gear ratio.

All that comes about because you make a wrong gedanken experiment of what the cart of the original poster WOULD do (according to you) when exposed in a wind tunnel.

You don't change the sails of your boat either when you do the equivalent frame transformation in the sea current versus wind case, do you ?

This is really very similar to the case of the winding of a wire on a wheel while you PULL on the wire. Only because of airodynamics, things are less evident.

It is very simple to test if my prediction is wrong or right...no need to argue endlessly about it. All swerdna has to do is reverse one cable and rerun the test. Then we will see. How difficult is that?

 

[schroder]

But where is the difference if you look upon this from the reference of the turning table ?

In what way can you say that the table is "really turning" and the air is "really stationary", and not that the table is actually standing still and the air is moving ? This is just a change of reference frame, no ?

(there IS a small difference, and that is the fact that the reference frame of the table also has a rotation which it shouldn't, as an inertial frame. But that can be made smaller with a larger turning table).

It is onvious that the reference frame with the spinning table is NOT equivocal to the frame with the table stationary and wind blowing in the back of the cart. It is the spin up of the wheel which is driving the propeller and the cart advances against the table. Now, change the frame so the table is statiuonary and the wind is the force on the propeller. The propeller will be driven the OPPOSITE way, the wheels will go the OPPOsite way and the cart goes upwind, not down! How can you possibly call these frames equivocal! Everything must behave in a way which is indistinguishable to an outside observer! Thai is certainly not the case here.. I am repeating myself, but you are refusing to listen. You think I am wrong? Then ask swerdna to place a fan on the cart with the table stationary and see if it goes downwind. I am betting it will not! Better yet, ask him to swap that cable I mentioned and run the test again. We might find out I am right. But we will never know if everyone refuses to even test it!

 

[zoobyshoe]

In relation to my original question can I assume the following . . .

Schroder and Zoobyshoe think DDWFTTW is impossible and not is not demonstrated by my turntable demonstrations and other demonstrations.

Jeff Reid, Vanesch and Phrak think DDWFTTW is possible and not is demonstrated by my turntable demonstrations and other demonstrations.

Is this correct?

No, I do not assert it is impossible. I have serious problems with the idea which no one has adequately cleared up for me. I haven't seen a demonstration that has convinced me. I remain skeptical.

 

[schroder]

No, I do not assert it is impossible. I have serious problems with the idea which no one has adequately cleared up for me. I haven't seen a demonstration that has convinced me. I remain skeptical.

I would say I am Highly Sceptical but I would not mind very much being proven wrong. With this turntable, we have a device which can easily prove the case, one way or the other. But in order to do that some additional tests need to be done. I have already described these very simple tests in detail. It remains to be seen if anyone will do them.

 

[zoobyshoe]

The reality of this I thought was cleared up since long in this forum, both by video verifications and theoretical explanations.

This is not a new Einsteinian theory demanding abstract inertial frames
to explain - it is just a gearbox between two media, ground and air, with different velocities. By gearing this gearbox suitably, this difference in speed of medias could give this gearbox (at least theoretically) any speed in any direction. It is just an engineering task - where of course every specific solution has its practical limitations.

The power from differences of speeds of surrounding media can be extracted rather independently of gearbox`s (=vehicle`s) own speed. As maybe some pointed out
earlier. This is egineering, not abstract difficult comprehensible science.

I just apprehended this: "The power from differences of speeds of surrounding media can be extracted rather independently of gearbox`s (=vehicle`s) own speed." Stated this way, it suddenly made sense.

 

[vanesch]

It is very simple to test if my prediction is wrong or right...no need to argue endlessly about it. All swerdna has to do is reverse one cable and rerun the test. Then we will see. How difficult is that?

I don't see what it will prove. If you inverse the gear ratio sign, then you will now have something that will not go backward faster than the wind. So ? What will this learn us ?

The experiment you propose is NOT the "equivalent" of this test.

 

[vanesch]

The reality of this I thought was cleared up since long in this forum, both by video verifications and theoretical explanations.

This is not a new Einsteinian theory demanding abstract inertial frames
to explain - it is just a gearbox between two media, ground and air, with different velocities. By gearing this gearbox suitably, this difference in speed of medias could give this gearbox (at least theoretically) any speed in any direction. It is just an engineering task - where of course every specific solution has its practical limitations.

The power from differences of speeds of surrounding media can be extracted rather independently of gearbox`s (=vehicle`s) own speed. As maybe some pointed out
earlier. This is egineering, not abstract difficult comprehensible science.

Yes, that was what my example in post https://www.physicsforums.com/showpost.php?p=2031426&postcount=96 made more explicit in post
https://www.physicsforums.com/showpost.php?p=2031533&postcount=136

 

[schroder]

I just apprehended this: "The power from differences of speeds of surrounding media can be extracted rather independently of gearbox`s (=vehicle`s) own speed." Stated this way, it suddenly made sense.

Really? So if a shopping cart is extracting power from someone pushing it, and that someone slows dow or stops pushing or just walk away, the cart can still extract power from the person walking away? Can a shopping cart go faster on level ground, than the person who is pushing it, in a continuous fashion? You might give it a mighty shove, but it will soon stop. Over any reasonable distance , it will never outrun you. And if you were not pushing the cart at all, you would cover the distance much faster. Same with the wind pushing that cart.

 

[schroder]

I don't see what it will prove. If you inverse the gear ratio sign, then you will now have something that will not go backward faster than the wind. So ? What will this learn us ?

The experiment you propose is NOT the "equivalent" of this test.

It will be something that can go downwind when pushed by the wind. And something which will go downwind on a turntable which simulates being pushed by the wind. Which is NOT what you have now! What you have now is a cart which will attempt to go upwind when pushed by the wind, and you are testing it in a downwind simulator! What does THAT learn us? Nothing!

What we will learn from doing it the correct way is that DDWFTTW does not work! But it seems no one wants to learn that, or do you?

 

[vanesch]

It is onvious that the reference frame with the spinning table is NOT equivocal to the frame with the table stationary and wind blowing in the back of the cart. It is the spin up of the wheel which is driving the propeller and the cart advances against the table. Now, change the frame so the table is statiuonary and the wind is the force on the propeller. The propeller will be driven the OPPOSITE way, the wheels will go the OPPOsite way and the cart goes upwind, not down!

But stop saying what you THINK that the propeller will do ! This is YOUR claim, and it is definitely wrong, given the behavior on the turntable. "Change the frame so that the table is stationary" means: change your *point of view* but everything happens of course the same way. It is not because you LOOK upon the same experiment differently that it behaves differently. And in this particular case, in the reference frame of the table, there IS a wind blowing in the direction of the cart and the cart IS moving faster back than the wind is blowing. You'd only need to put a webcam ON THE TURNING TABLE instead of fixed in the lab, and you have your change of reference frame.

How can you possibly call these frames equivocal! Everything must behave in a way which is indistinguishable to an outside observer! Thai is certainly not the case here..

It is not the case because you PRETEND that it will behave differently. That is as saying: look, a glass in a train with some wine in it is not the same as a glass on a table next to the railway. Because of course the wine in the train will bend over in one direction, and hence, it cannot be a frame transformation, because otherwise it would mean that the wine would be horizontal and clearly it isn't.

 

[vanesch]

Really? So if a shopping cart is extracting power from someone pushing it, and that someone slows dow or stops pushing or just walk away, the cart can still extract power from the person walking away? Can a shopping cart go faster on level ground, than the person who is pushing it, in a continuous fashion?

Of course. One way is calling it a bicycle. Another example is the wheel with the rope. If you pull slowly on the rope, the wheel will come faster towards you than you try to walk away from it (see my post 96, first attachment).

 

[pallidin]

Really? So if a shopping cart is extracting power from someone pushing it, and that someone slows dow or stops pushing or just walk away, the cart can still extract power from the person walking away? Can a shopping cart go faster on level ground, than the person who is pushing it, in a continuous fashion? You might give it a mighty shove, but it will soon stop. Over any reasonable distance , it will never outrun you. And if you were not pushing the cart at all, you would cover the distance much faster. Same with the wind pushing that cart.

A shopping cart is not geared. But if it were, say, with a 2:1 ratio, than as you pushed it it would move at twice your pushing speed but half the force, thus quickly leaving your hands, then eventually stopping as no further input force is applied.

 

[schroder]

But stop saying what you THINK that the propeller will do ! This is YOUR claim, and it is definitely wrong, given the behavior on the turntable. "Change the frame so that the table is stationary" means: change your *point of view* but everything happens of course the same way. It is not because you LOOK upon the same experiment differently that it behaves differently. And in this particular case, in the reference frame of the table, there IS a wind blowing in the direction of the cart and the cart IS moving faster back than the wind is blowing. You'd only need to put a webcam ON THE TURNING TABLE instead of fixed in the lab, and you have your change of reference frame.



It is not the case because you PRETEND that it will behave differently. That is as saying: look, a glass in a train with some wine in it is not the same as a glass on a table next to the railway. Because of course the wine in the train will bend over in one direction, and hence, it cannot be a frame transformation, because otherwise it would mean that the wine would be horizontal and clearly it isn't.

I am not pretending anything! Do you understand the pitch of a propeller at All? A propeller turning and cutting into the air aheasd has a Leading pitch, and it shoves the air in front backwards. If you now blow wind on that propeller from the back, that same pitch will exert a normal force on the pitched blades which WILL turn the blades in the opposite direction. This is so incredibly easy to prove that I am surprised you question it! Do you own two electric fans? That is all you need to demonstrate this. If swerdna will simply let a fan blow on the propeller from the same direction the relative wind is coming from, it will definitely turn in the opposite direction it turns in the video. I do not THINK so, I KNOW so. It cannot do anything else!

 

[zoobyshoe]

Really? So if a shopping cart is extracting power from someone pushing it, and that someone slows dow or stops pushing or just walk away, the cart can still extract power from the person walking away? Can a shopping cart go faster on level ground, than the person who is pushing it, in a continuous fashion? You might give it a mighty shove, but it will soon stop. Over any reasonable distance , it will never outrun you. And if you were not pushing the cart at all, you would cover the distance much faster. Same with the wind pushing that cart.

Quiet, I'm cogitating. And the zoobie brain is a slow, rust-encrusted, squealing, steam- emitting, gear-grinding, contraption with lots of loose hoses and shorted wires, and no one remembers the last oil change.

 

[schroder]

Of course. One way is calling it a bicycle. Another example is the wheel with the rope. If you pull slowly on the rope, the wheel will come faster towards you than you try to walk away from it (see my post 96, first attachment).

The point was: Pushing it.

 

[swerdna]

I went to the trouble and expense of building this equipment because I want to find out if DDWFTTW is possible or not. On the face of it the claim doesn’t make sense to me and I expected that my tests would be more likely to disprove the claim than prove it. It has turned out however that they seem to have done the opposite and I want to know if my interpretation of the tests are correct or not.

I had some reservations about the treadmill demonstrations that were being offered and these reservation were as follows . . .

Holding the wheels of a cart against a moving surface until they reach the speed of the surface is like pushing a cart up to wind speed in an outside test and doesn‘t represent the cart getting the energy to do this from the wind or prove that it could do so. A treadmill simply isn‘t long enough to allow the cart to get the speed from the apparent wind on it‘s own accord.

Holding the wheels of a cart against a moving surface beyond the point where the thrust of the prop would otherwise have moved the cart forward against the surface is “boosting” that forward motion. In other words a cart that would never be able move against a moving surface on it’s “own accord” can be forced to do so by artificially holding it against the surface and then releasing it. I may provide a video demonstration of what I mean.

Because I believe a cart can be artificially forced to move forward against the motion of a moving surface I was never happy that a treadmill demonstration could adequately demonstrate that the forward movement wasn’t some temporary effect of stored energy that was being lost to friction very gradually.

Because a treadmill is of limited length the cart can’t move backward or forward much and doesn’t gain the same amount of inertia that it would moving along the ground outside. Not sure if this is important but it is something that is not equivalent to and outside test.

A turntable is essentially a treadmill of indefinite length and I believe overcomes all these treadmill “problems”.

As far as I can tell the tests I have done have demonstrated that the thrust of the propeller can be greater than the rolling resistance. Also that there is no form of stored energy involved as I have run the cart opposing the surface direction for over 10 minutes with no apparent loss of speed. I have also physically slowed the cart while it is running and it quickly returned to it’s “cruise” speed.

Sorry if the layman’s wording I’ve used is confusing.

 

[pallidin]

The point was: Pushing it.

Doesn't one "push" on bicycle pedals?

 

[swerdna]

I would say I am Highly Sceptical but I would not mind very much being proven wrong. With this turntable, we have a device which can easily prove the case, one way or the other. But in order to do that some additional tests need to be done. I have already described these very simple tests in detail. It remains to be seen if anyone will do them.

I would be very happy to perform any test that you suggest as long as it makes some sense and is possible. This thread is moving very fast and I’m behind a heap of previous posts without even keeping up with the new ones. Rather than me looking through heaps of posts to find out what test you want could you please explain (again) exactly what test you want me to conduct and what the purpose of the test is and what will it is designed to prove.

 

[schroder]

I went to the trouble and expense of building this equipment because I want to find out if DDWFTTW is possible or not. On the face of it the claim doesn’t make sense to me and I expected that my tests would be more likely to disprove the claim than prove it. It has turned out however that they seem to have done the opposite and I want to know if my interpretation of the tests are correct or not.

I had some reservations about the treadmill demonstrations that were being offered and these reservation were as follows . . .

Holding the wheels of a cart against a moving surface until they reach the speed of the surface is like pushing a cart up to wind speed in an outside test and doesn‘t represent the cart getting the energy to do this from the wind or prove that it could do so. A treadmill simply isn‘t long enough to allow the cart to get the speed from the apparent wind on it‘s own accord.

Holding the wheels of a cart against a moving surface beyond the point where the thrust of the prop would otherwise have moved the cart forward against the surface is “boosting” that forward motion. In other words a cart that would never be able move against a moving surface on it’s “own accord” can be forced to do so by artificially holding it against the surface and then releasing it. I may provide a video demonstration of what I mean.

Because I believe a cart can be artificially forced to move forward against the motion of a moving surface I was never happy that a treadmill demonstration could adequately demonstrate that the forward movement wasn’t some temporary effect of stored energy that was being lost to friction very gradually.

Because a treadmill is of limited length the cart can’t move backward or forward much and doesn’t gain the same amount of inertia that it would moving along the ground outside. Not sure if this is important but it is something that is not equivalent to and outside test.

A turntable is essentially a treadmill of indefinite length and I believe overcomes all these treadmill “problems”.

As far as I can tell the tests I have done have demonstrated that the thrust of the propeller can be greater than the rolling resistance. Also that there is no form of stored energy involved as I have run the cart opposing the surface direction for over 10 minutes with no apparent loss of speed. I have also physically slowed the cart while it is running and it quickly returned to it’s “cruise” speed.

Sorry if the layman’s wording I’ve used is confusing.

You have done a nice job and have contributed greatly to this discussion. But what you have still does not "prove" DDWFTTW. Are you willing to do a few more tests with your set up?

 

[swerdna]

You have done a nice job and have contributed greatly to this discussion. But what you have still does not "prove" DDWFTTW. Are you willing to do a few more tests with your set up?

Yes please - This is what I want!