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

[zoobyshoe]

Since power = force times speed, the DDWFTTW cart can take advantage of the fact that apparent headwind speed is < ground headwind speed, because advancing the air through the prop at a lower speed than ground speed allows the force from the prop to be greater than the opposing force from the ground, without consuming more power than is generated by the ground + wheel interface.

The power available to the cart at this point from the ground as headwind is directly proportional to the cart's total momentum: its mass x its velocity, plus whatever momentum is stored in the prop and tires as flywheels. From this point forward it's all consumption: there's no more energy input into the cart system.

 

[vanesch]

This isn't a good model of the DDWFTTW cart. The force from the prop is a function of v_wind as well as v_cart.

That's why there is the second term in the first equation, which depends on the "seen" wind velocity. It includes not only passive drag, but also whatever effect it has on the prop.

Except that large A doesn't mean high gearing ratio, but instead high force, such as a larger diameter. A is defined to be a force here, so it would have to be negative to create an upwind cart.

For a downwind cart, it is a positive number (after all, for a downwind cart, the propeller acts as a propeller which is driven by the wheels: there is power flowing from the wheels to the propeller). For an upwind cart, I guess indeed that it works as a turbine, so A should be negative.

One requirement for a DDWFTTW cart is that the forward force from the prop + air interface is larger than the opposing backwards force from the wheel + ground interface that powers the propeller, so that the net forward force (prop force - wheel force) accelerates the cart or maintains a DDWFTTW speed against the opposing drag related forces. The other requirement is that the forward force > opposing force is achieved while the power output is less than the power input.

Since power = force times speed, the DDWFTTW cart can take advantage of the fact that apparent headwind speed is < ground headwind speed, because advancing the air through the prop at a lower speed than ground speed allows the force from the prop to be greater than the opposing force from the ground, without consuming more power than is generated by the ground + wheel interface.

Indeed. That's why this thing is not an over-unity device: the same force *taking* power from the ground (which moves faster than the wind) takes in more power than it costs power applying that same force (in the other direction) to the air (which moves slower). I already started writing two posts on this power balance, but each time I got distracted, and wasn't happy with what I wrote, so I deleted them.

 

[schroder]

In spork's treadmill videos, he pushes the cart so it's moving backwards, a T-H situation, and once free, the cart responds by accelerating forwards back into a H-H situation. In swerdna's 2nd video, the cart is moving at the same speed as the turntable because of the block held by the fishing line. When the block is realeasd, the cart is in a T-0 situation (no relative ground movement), it transitions into a T-H situation, then continues on into a H-H situation. Why don't you consider these videos as "evidence"

I do not accept these as evidence of a transition because the transition is into a simulated H-H situation, and not an actual example of a H-H situation. It is simulated because the ground is moving and being powered by a Motor! In the true H-H situation, the ground is stationary, the cart is moving but it does not have a motor to drive it! Let’s assume the cart is somehow pushed into a true transition to H-H. What exactly is supposed to keep it there? The ground is stationary, the wind is a headwind against the cart. Just exactly what is supposed to keep the cart moving forwards? You absolutely cannot say that because it is happening on the treadmill, it will happen in the real world situation because there is NO MOTOR! Why is that so difficult to comprehend? I stress that the treadmill/turntable situation is a simulation only and NOT an actual example of DDWFTTW. Give it some thought, please.

 

[rcgldr]

The power available to the cart at this point from the ground as headwind is directly proportional to the cart's total momentum.

I'm using the cart itself as a frame of reference here. Power equals force time speed. The power output is the thrust from the prop times the speed of the air through the prop. The torque required to produce the power at the prop is transferred to the driving wheels which apply a forwards force to the ground which reacts with an equal and opposing backwards force (Newton 3rd law pair). The power input to drive the prop is this backwards force from the ground times the speed of the ground.

 

[schroder]

My Final Analysis:
The treadmill/turntable demonstrations are exactly equivocal to a motorized cart running into a headwind. They have nothing at all to do with a wind-powered cart going downwind faster than the wind.

 

[rcgldr]

I do not accept these as evidence of a transition because the transition is into a simulated H-H situation, and not an actual example of a H-H situation. It is simulated because the ground is moving.

Ok, so let put a cart outdoors facing west at about latitude 89.44 of the Earth. Relative to the north pole, the ground is moving eastward at 10 mph. Say the wind is moving at 0 mph relative to the north pole. Initially the cart experiences an apparent tailwind of 10 mph and accelerates west. As the cart speeds up, the apparent wind transitions to 0, and then into a headwind. Say the cart reaches terminal velocity at 4 mph west, relative to the north pole. At this point the westward facing cart experiences an apparent wind of -4 mph, and an apparent ground speed of -14 mph. How is this significantly different than the turntable?

 

[zoobyshoe]

I'm using the cart itself as a frame of reference here. Power equals force time speed. The power output is the thrust from the prop times the speed of the air through the prop. The torque required to produce the power at the prop is transferred to the driving wheels which apply a forwards force to the ground which reacts with an equal and opposing backwards force (Newton 3rd law pair). The power input to drive the prop is this backwards force from the ground times the speed of the ground.

I am also using the cart as the frame of reference. Since the wind is 0 the only power source is now the ground. The only energy available from the ground happens to be equal to the energy represented by the cart's momentum, which is limited. The cart can use some of it to accelerate some air. It doesn't gain energy from this as it does when encountering fast air and leaving slowed down air in its wake.

Slowing the wind down is how any wind powered device extracts energy from the wind.

Now the cart is encountering slow air and leaving it faster in its wake. The whole cart system is losing energy.

 

[atyy]

The closest I can come to making sense of schroder's objection is: have the forces been correctly transformed in switching frames?

 

[rcgldr]

Since the wind is 0 the only power source is now the ground.

There's a spinning prop producing thrust when the apparent wind is 0. The prop rate of rotation is related to ground speed, not apparent wind speed.

Slowing the wind down is how any wind powered device extracts energy from the wind.

Now the cart is encountering slow air and leaving it faster in its wake. The whole cart system is losing energy.

The prop is slowing the air down to a speed less than that of the cart's forward speed. For example, a 10 mph taiwind, a cart moving at 14 mph, and the prop generating upwind thrust at 6 mph. The thrust from the prop slows the 10 mph tailwind down to 8 mph, and this is the source of energy that propels the cart DDWFTTW.

 

[Subductionzon]

zoobyshoe, the air still has a different speed than the ground in your frame of reference. The air is still and the ground is moving backwards at 10 mph (for a ten mph tailwind and the cart matching windspeed). So if the cart changes the speed of the wind so it is closer to the ground speed then is has taken some of the potential energy out of that wind and it can be used to raise the speed of the cart, enabling it to go downwind faster than the wind. The carts energy comes from the difference between air speed and ground speed, something that will exist regardless of the cart's speed. This cart is just an elegant way of harvesting that potential energy.

 

[schroder]

Ok, so let put a cart outdoors facing west at about latitude 89.44 of the Earth. Relative to the north pole, the ground is moving eastward at 10 mph. Say the wind is moving at 0 mph relative to the north pole. Initially the cart experiences an apparent tailwind of 10 mph and accelerates west. As the cart speeds up, the apparent wind transitions to 0, and then into a headwind. Say the cart reaches terminal velocity at 4 mph west, relative to the north pole. At this point the westward facing cart experiences an apparent wind of -4 mph, and an apparent ground speed of -14 mph. How is this significantly different than the turntable?

It is significantly different because it is only a product of your imagination! Nothing of that sort has ever been demonstrated. If you would like to perform such a demonstration, I would be happy to witness and sign off on it!

 

[vanesch]

The closest I can come to making sense of schroder's objection is: have the forces been correctly transformed in switching frames?

When you switch inertial frames, forces don't change (that is, the vectors remain the same - their component values can change of course if there is a rotation of axes).

When you switch from an inertial frame to a rotating frame, you have to add centrifugal and coriolis forces. (hence my caveat).

 

[vanesch]

It is significantly different because it is only a product of your imagination! Nothing of that sort has ever been demonstrated. If you would like to perform such a demonstration, I would be happy to witness and sign off on it!

But, if that demonstration doesn't work, we have established a case in which galilean transformations do not work! We have established that Newtonian mechanics is basically flawed if the demonstration would work on a treadmill but not in a "real wind" situation. It would mean that physics is different in different reference frames.
We could use then such a device to find out what is the "absolute 0 speed".

(up to the caveat of the rotating frame).

 

[atyy]

When you switch inertial frames, forces don't change (that is, the vectors remain the same - their component values can change of course if there is a rotation of axes).

Is this also true for velocity dependent forces?

 

[zoobyshoe]

There's a spinning prop producing thrust when the apparent wind is 0. The prop rate of rotation is related to ground speed, not apparent wind speed.

The ground speed when the wind is 0 is the same speed as the former tailwind speed over the ground. The ground has a v = TWS but the ground's mass is deceptively small in this case: it is only equal to the mass of the cart. It will only apply torque to the wheels equal to the torque the cart exerts on the ground. It will slow the ground down pretty quickly once you press that torque into service accelerating air.

The prop is slowing the air down to a speed less than that of the cart's forward speed.

Extracting energy from the wind is not accomplished by slowing the wind down relative to your own speed. It is accomplished by slowing the wind relative to the wind's previous speed. It is slower because it has imparted some of its energy to the blades of the windmill. To give energy to the windmill it must lose something: speed.

 

[schroder]

But, if that demonstration doesn't work, we have established a case in which galilean transformations do not work! We have established that Newtonian mechanics is basically flawed if the demonstration would work on a treadmill but not in a "real wind" situation. It would mean that physics is different in different reference frames.
We could use then such a device to find out what is the "absolute 0 speed".

(up to the caveat of the rotating frame).

Well, I see two ways of looking at this:
1) If we are correctly interpreting what is happening on the treadmill/turntable, and the outdoor test fails to duplicate the result, then we have proved an inconsistency with Newton mechanics and Galilean reference frames.
2) If the outdoor test fails to duplicate the result obtained on the TT, it means we have not been accurately interpreting what is happening on the TT.

I do not for one second think that we are about to discover something inconsistent with Newtonian mechanics or reference frames. I do firmly believe, as I have said from day one on this subject, that we are not correctly interpreting what is happening on the TT or TM. The “ground” being driven by a motor in one frame can only be reciprocated by a motorized cart in the corresponding frame in my opinion. I don’t see how anyone can say a cart with no motor can advance against a stationary ground and an effective headwind. It has no power source. In my opinion, what is happening here is we are making a misjudgment of what is happening on the TT/TM and now trying to explain it within the laws of physics. Unfortunately, the laws of physics cannot explain it, so we are inventing parameters such as energy from the ground air interface and we cannot see the forest any more because of all the trees we have planted! I suggest we fall back and re-evaluate what is happening on the TT/TM and I believe you will all find that there has been a serious misinterpretation there. I believe that is what Atyy is alluding to.

 

[A.T.]

I do not accept these as evidence of a transition because...

Because you still haven't mastered http://en.wikipedia.org/wiki/Galilean_relativity"

It is simulated because the ground is moving and being powered by a Motor! In the true H-H situation, the ground is stationary,

What do you mean by "stationary"? The Earth moves around the sun at 30 km/s. There is no such thing in physics as absolute rest. The ground outside can be assumed to be stationary just like the conveyor belt of the treadmill can be too. Both views are valid. Neither one is 'simulated' or less real.

Let’s assume the cart is somehow pushed into a true transition to H-H. What exactly is supposed to keep it there?

The same thing that keeps http://de.youtube.com/watch?v=9Yt4zxYuPzI&feature=related" going against the ground and the ruler: translation.

You absolutely...

Stop thinking in absolute terms. Movement is relative.

... cannot say that because it is happening on the treadmill, it will happen in the real world situation because there is NO MOTOR!

Yes there is a motor called sun. It drives the air masses just like the electric motor is driving the conveyor belt of the treadmill.

 

[zoobyshoe]

zoobyshoe, the air still has a different speed than the ground in your frame of reference. The air is still and the ground is moving backwards at 10 mph (for a ten mph tailwind and the cart matching windspeed). So if the cart changes the speed of the wind so it is closer to the ground speed then is has taken some of the potential energy out of that wind and it can be used to raise the speed of the cart, enabling it to go downwind faster than the wind. The carts energy comes from the difference between air speed and ground speed, something that will exist regardless of the cart's speed.

But to change some of the wind speed so it is closer to ground speed it must take energy from the ground by slowing it down. The ground now has less speed. As soon as that happens we're back in a TH.

 

[vanesch]

Is this also true for velocity dependent forces?

Yes, because in order for forces to have a physical meaning and be velocity-dependent, they have to be velocities BETWEEN objects, which are themselves invariant under change of reference frame. There are no forces which are dependent on velocities wrt the reference frame.

That is, for instance, the force on the propeller will be dependent on the velocity of the air wrt the propeller. That velocity is independent of the frame in which it is observed, because it is calculated by the difference of the two velocities (wrt the frame) of the two objects. If you switch frames, you add the same "transformation" velocity to the two velocities, and this drops out in the difference.

In just any frame, the velocity of the air wrt the propeller is the same (but it is calculated differently of course).

 

[schroder]

Because you still haven't mastered http://en.wikipedia.org/wiki/Galilean_relativity"

Yes, that must be the explanation! I was wondering when the thread would degenerate into this sort of mud slinging.

A.T. : “What do you mean by "stationary"? The Earth moves around the sun at 30 km/s. There is no such thing in physics as absolute rest.”

So this cart harvests power from the rotation of the Earth around the sun? It is an even bigger breakthrough than I thought!

A.T. : “Yes there is a motor called sun. It drives the air masses just like the electric motor is driving the conveyor belt of the treadmill”

So now it is extracting solar energy as well? Where are the solar panels? Why not just put a battery and DC motor in it as well.

I don’t see that anything you have posted here has any relevance to this thread.

 

[vanesch]

Well, I see two ways of looking at this:
1) If we are correctly interpreting what is happening on the treadmill/turntable, and the outdoor test fails to duplicate the result, then we have proved an inconsistency with Newton mechanics and Galilean reference frames.
2) If the outdoor test fails to duplicate the result obtained on the TT, it means we have not been accurately interpreting what is happening on the TT.

I do not for one second think that we are about to discover something inconsistent with Newtonian mechanics or reference frames.

Ah, that's a relief

I do firmly believe, as I have said from day one on this subject, that we are not correctly interpreting what is happening on the TT or TM. The “ground” being driven by a motor in one frame can only be reciprocated by a motorized cart in the corresponding frame in my opinion.

But in the "true windtunnel test" the wind is motor-driven. OF COURSE the energy comes from the motor.

I don’t see how anyone can say a cart with no motor can advance against a stationary ground and an effective headwind.

Well, nevertheless, that's what a sailing car can do.

It has no power source. In my opinion, what is happening here is we are making a misjudgment of what is happening on the TT/TM and now trying to explain it within the laws of physics. Unfortunately, the laws of physics cannot explain it, so we are inventing parameters such as energy from the ground air interface and we cannot see the forest any more because of all the trees we have planted! I suggest we fall back and re-evaluate what is happening on the TT/TM and I believe you will all find that there has been a serious misinterpretation there. I believe that is what Atyy is alluding to.

But you only formulate "opinion" here, and you give no indication as to where, looking from a different reference frame, there is the slightest difference between the situation you want to see "stationary ground and real wind" and the actual situation "moving ground and steady air mass". Do you actually know what it means to change reference frames ? No offense, but you insisting so much on this "difference" makes me wonder.
There *are* a few differences, such as the fact that it is a rotating frame, and maybe that there are some aerodynamical differences (there might be some air dragged along with the turntable, so that the air mass is not entirely stationary etc...).

 

[schroder]

But in the "true windtunnel test" the wind is motor-driven. OF COURSE the energy comes from the motor.






Do you actually know what it means to change reference frames ? No offense, but you insisting so much on this "difference" makes me wonder.
There *are* a few differences, such as the fact that it is a rotating frame, and maybe that there are some aerodynamical differences (there might be some air dragged along with the turntable, so that the air mass is not entirely stationary etc...).

But once the cart exceeds the windspeed (assuming it ever does) the force of the wind and the motor driving the wind, is gone. However, in the simulation on the TT, the motor force is always present. That, to me, is a very BIG difference.

Yes, I actually do know quite a lot about reference frames.

 

[vanesch]

But to change some of the wind speed so it is closer to ground speed it must take energy from the ground by slowing it down. The ground now has less speed. As soon as that happens we're back in a TH.

As I said much earlier in this thread, you are running into a Zeno-type paradox here. That is because you are analyzing things which happen *simultaneously* and you apply them *sequentially*.

What happens is that you TAKE power from the link with the ground (from the wheels), and you GIVE it to the air (with the propeller), and that for a given power, this causes a SMALLER braking force on the wheels than it gives you a "pulling force" with the propeller. These forces are applied simultaneously, and because the propeller "wins", the net force is forward, in the wind direction.

And that's because the power you extract from the wheels equals the velocity of the ground (wrt the cart) times the "braking force" which is the reaction of taking away power, while (ideally) the force you can give to the air is equal to the air velocity (wrt the cart) times the "pulling force" by the propeller (minus the losses due to drag and so on).

When the air is "at rest", that force can actually be as big as you want (with a big enough propeller which moves slowly enough - think ultimately of a giant paddle wheel with huge sails on them).

 

[vanesch]

But once the cart exceeds the windspeed (assuming it ever does) the force of the wind and the motor driving the wind, is gone.

Once the cart exceeds windspeed, it takes its power from the wheels, and puts it into the air, like a propeller-driven airplane. In the overall power balance, this has slowed down some air mass (which has been projected UPWIND by the propeller), and this is the ultimate energy source in the "fixed ground and flowing air" system. So the wind is moving slower in the wind tunnel than it would have been without the propeller blowing upwind. That's the source of the energy. Even if the propeller itself is moving faster than the wind, it STILL blows the air somewhat upwind.

Remember that kinetic energy is frame-dependent. So which medium "wins" energy and which one "looses" is dependent on from which frame you look upon it.

In the turntable test, as seen from the lab system, it is the "braking power" of the wheels which brakes the table, and this is compensated by the motor of the turntable. The air WINS some power here, because it was stationary, and now it is set into motion by the propeller (in the same direction as the turntable).

But if you do the energy balance of this turntable thing in the frame that moves with the turntable, then the air had initially a higher velocity than afterwards, and so now it is the air that delivered the energy, given by the motor which turned the Earth (and the air) underneath the stationary turntable.

The motor (rotating the Earth and the room) is acting as the ventillator in the windtunnel.

 

[rcgldr]

It will only apply torque to the wheels equal to the torque the cart exerts on the ground. It will slow the cart down pretty quickly once you press that torque into service accelerating air.

Except in this case the the torque pressed into service to accelerate the air ends up being converted by the propeller into thrust that is greater than the torque related opposing force from the ground. This works because the propeller interacts with a headwind that is much slower than the ground speed, and although force is higher, speed is slower still, and power output is less than power input.

Extracting energy from the wind is accomplished by slowing the wind relative to the wind's previous speed.

Which is what is happening with the DDWFTTW cart. Repeating my previous example, the wind speed is 10 mph, the cart speed is 14 mph, and the prop accelerates the air by 6 mph upwind. The air speed at the prop is 14 mph - 6 mph = 8 mph. The prop is slowing down the wind from 10 mph to 8 mph, even though it's moving forwards at 14 mph. This 2 mph reduction in wind speed is what is powering this example cart. The videos we've seen appear to confirm that these DDWFTTW cart work.

 

[schroder]

Once the cart exceeds windspeed, it takes its power from the wheels, and puts it into the air, like a propeller-driven airplane. In the overall power balance, this has slowed down some air mass (which has been projected UPWIND by the propeller), and this is the ultimate energy source in the "fixed ground and flowing air" system. So the wind is moving slower in the wind tunnel than it would have been without the propeller blowing upwind. That's the source of the energy. Even if the propeller itself is moving faster than the wind, it STILL blows the air somewhat upwind.

OK. It takes its power from the wheels. Would you kindly tell me where the wheels are taking their power from? Ultimately it has to come from somewhere. Let's trace it back to the source, please.

 

[vanesch]

OK. It takes its power from the wheels. Would you kindly tell me where the wheels are taking their power from? Ultimately it has to come from somewhere. Let's trace it back to the source, please.

I edited my previous post a bit in the mean time.

But the source is always the source of power that establishes the difference in velocity between the air mass and the ground. In the turntable test, this is the motor that runs the table, in the windtunnel test, it is the motor that drives the ventilator, and outdoor, it is the sun that drives the wind.

 

[schroder]

I edited my previous post a bit in the mean time.

But the source is always the source of power that establishes the difference in velocity between the air mass and the ground. In the turntable test, this is the motor that runs the table, in the windtunnel test, it is the motor that drives the ventilator, and outdoor, it is the sun that drives the wind.

It seems to me that the power budget is making a complete circle, and you know what that means...pmm. I'm sorry, I don't have any more time today to discuss this. I don't think the issue is settled. Thank you for your time and insights. I do respect your opinion and analysis.

 

[rcgldr]

I was wondering when the thread would degenerate into this sort of mud slinging.

Come on guys we can discuss this without the implied insults.

So this cart harvests power from the rotation of the Earth ... and the sun?

The cart harvests power from the wind. There are all multiple reasons why there are winds on the earth, including the Earth's rotation, and the heat from the sun. It doesn't really matter, as we know that winds exist, and we know that a large wind turbine can generate mega-watts of power. This would seem to prove that power can be extracted by slowing down the wind.

I'm assuming that you agree that slowing down the wind is suffcient to extract power from the wind? If so, then the only remaining issues are if a propeller on a cart can slow down the wind even though the cart and propeller are moving DDWFTTW, and do so without consuming more power than the wind is providing.

 

[vanesch]

It seems to me that the power budget is making a complete circle, and you know what that means...pmm.

So we are back to your initial claim that a DWFTTW is an over-unity device, and hence must be able to be proved against classical mechanics. As I said, I would like to see your proof of that - as I've given gedanken experiments that comply with classical mechanics' postulates and are nevertheless moving DWFTTW (by planting windmills and all those other strange examples).

But your claim is not true. There is an external source of power, which is whatever establishes the difference in velocity between the two media (air and ground). I don't see why you find this obvious in the turntable setup (YES, the power comes from the motor), but refuse to acknowledge that in a "fixed ground but moving air" frame (such as the lab frame in a wind tunnel experiment) the power comes from whatever makes the air move - such as the ventillator that drives the wind tunnel.

After all, as Jeff said, with a windmill it is also possible to extract power from this - so is this then also an over-unity device ?