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Down wind faster than the wind

humber said:
If you mean a powered treadmill and wind, then there would be two independent power sources. That would not be acceptable.
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A powered treadmill and no wind only has one power source; would that be acceptable?


There still seems to be a problem with the definition of windspeed:

Even at "windspeed" the air velocity between the cart and the wind will not be zero.
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If you are referring to the effects of wind shear with the ground that is correct. But under the definition of wind speed I proposed above, there is a definite speed of the wind so it can be determined if the cart is traveling at that speed.
 
John Freestone said:
I don't understand that part. Isn't energy part of the equations of motion?
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Sort of. One of the equations of motion is that the total energy is conserved - i.e. it doesn't change with time. But that doesn't tell you what its value is, of course. When you boost, you change the value of the total energy, but in any frame it's conserved.

No that can't be. You mean something else? "Energy is not conserved by boosts" is the bit. Oh wait, crash walls into cars, the wall has the k.e. and vice versa? Wind has the energy, transfered to cart, on the road; the treadmill has the energy, which is being transfered to the cart? But aren't these dependent on the speed and the mass, and thus relative, too? I mean, don't all these bodies have great kinetic energy measured from the POV of the sun?
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Right: energy is relative. Technically speaking it's the time component of a 4-vector, which means it isn't invariant under coordinate transformations like boosts.
 
Dan,

Humber is NEVER going to honor that simple pledge he made. I'm very sorry to say that you're wasting your breath.

Personally I think the only hope (and it's a darn slim one), is to agree to let JREF be the independent tester. You can each make your case to them, provide them with treadmills, carts, physics papers, or whatever you like. And in the end they make their determination. But neither you nor humber gets to debate each other about the terms of the bet, testing methods, definition of wind, etc.

Like I said, I doubt VERY much humber will go for this, or any, arrangement. But if he does, you'll win.
 
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Dan O. said:
A powered treadmill and no wind only has one power source; would that be acceptable?

Then this would be another version of the existing treadmill? There must be wind, I think.

In my proposal, I was looking for a way of replicating Platt's idea, without having to provide a moving source.
A wind tunnel would need to be long, but holding the cart in the windflow and then releasing it, may make for a more practical length.





There still seems to be a problem with the definition of windspeed:



If you are referring to the effects of wind shear with the ground that is correct. But under the definition of wind speed I proposed above, there is a definite speed of the wind so it can be determined if the cart is traveling at that speed.
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I was referring to my proposal, which is no longer a candidate.

Windspeed for the cart is said to occur when there is no differential velocity between the cart and the wind. The other definition is that the cart is traveling at the same velocity as the measured velocity of the wind.
As long as the second definition is met, then I am not concerned about the other. I accept your earlier definition of the speed of the wind itself. Sorry, I should have said that earlier
 
spork said:
Dan,

Humber is NEVER going to honor that simple pledge he made. I'm very sorry to say that you're wasting your breath.

Personally I think the only hope (and it's a darn slim one), is to agree to let JREF be the independent tester. You can each make your case to them, provide them with treadmills, carts, physics papers, or whatever you like. And in the end they make their determination. But neither you nor humber gets to debate each other about the terms of the bet, testing methods, definition of wind, etc.

Like I said, I doubt VERY much humber will go for this, or any, arrangement. But if he does, you'll win.
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It doesn't look to me that you have made much preparation for the acceptance of your wager. What are you proposing for that event?

To help us along, can you please tell me what happens to the cart on the treadmill, when the propeller's bias is reversed from its current state?

The cost of directly involving JREF would be high. In any event, they would have to use a method that would satisfy the usual standards of evidence. There is no reason why a preliminary test could not satisfy both parties, or to see if such a test could be mutually agreed.
 
Don't forget to stipulate the relative velocities of the air and ground in the test.

Humber, maybe you should clarify what you mean by the present bias of the propeller and why you feel that reversing it (or not) should be included in a test description.
 
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mender said:
Don't forget to stipulate the relative velocities of the air and ground in the test.

Humber, maybe you should clarify what you mean by the present bias of the propeller and why you feel that reversing it (or not) should be included in a test description.
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It is not part of the test itself, but to see what potential lies in the treadmill approach. Currently, I can't see how it can be used.

As I understand it, the propeller is biased so that wind from the front of the cart rotates it CCW, and it is most efficient this way. Only a small amount of thrust is generated when rotated CW ? Flipping the prop on the shaft should then generate more thrust. If it is already in that state then it is at maximum thrust, so the test won't work.
If not, then I expect that the cart will move down the belt, because there is not enough friction to support the load that the increased thrust represents.
 
Just to be sure we are meaning the same thing, please review this video that shows the cart moving forward slowly enough to clearly see what the prop bias and rotation is.

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

Is this what you are meaning by the prop moving CCW when moving forward and viewed from the front (CW from the rear as seen in the video) and pitched so as to move air front to rear relative to the prop?
 
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mender said:
Just to be sure we are meaning the same thing, please review this video that shows the cart moving forward slowly enough to clearly see what the prop bias and rotation is.

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

Is this what you are meaning by the prop moving CCW when moving forward and viewed from the front (CW from the rear as seen in the video) and pitched so as to move air front to rear relative to the prop?
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Yes, that is the same as the other videos. When driven by the belt, the propeller rotates CW, when viewed from the rear. Perhaps I can put it another way. If the wheels are driven CW as on the belt, in which direction is the thrust generated, and is that more or less than the thrust when the wheels are driven CCW?
 
Humber, we need to both stay focused. Wining the wager is not the goal but the means of reaching the goal of finding the truth. When we complete this quest and one of us discovers how we had deluded ourself, the $100 donation will be a small price to pay for the knowledge we will have gained.

As we proceed, we need to insure that there are no misunderstandings. If a statement is not understood, ask for clarification. Only when we mutually agree on all the parameters of the test will the results be mutually accepted.

I believe we could both accept the results of a properly conducted outdoor test on solid ground and with real wind. But there are many variables in that test that cannot be controlled. If you ever watched a field of long grass in the wind you would know that the wind is never constant. There will be shifts in the wind that make determination of "down wind" indeterminate and there will be rolls and gusts that make the speed of the wind indeterminate. Even waiting for acceptable wind conditions makes the testing time indeterminate. These factors may preclude convincing JREF to facilitate this test so it would be to our mutual benefit to find a controlled indoor test that is satisfactory.
 
Just had this brief conversation with my son . . .

Son - “So you’re going to spend time and money building this thing that you’re fairly sure won’t work?”

Me - “Yes”

Son - “And even if it does work it doesn’t have any practicle use?”

Me - “Yes”

Son - “ Are you sure you’re my father?”

Me - “Ask your mother.”
 
humber said:
Yes, that is the same as the other videos. When driven by the belt, the propeller rotates CW, when viewed from the rear. Perhaps I can put it another way. If the wheels are driven CW as on the belt, in which direction is the thrust generated, and is that more or less than the thrust when the wheels are driven CCW?
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The thrust is from front to back, acting to propel the cart forward when the cart is moving forward.

I'm not sure I'm understanding what you mean by turning the wheels CCW. It may help to consider the wheels always turning the same way and either talk about the prop pitch or rotation being reversed to switch the direction of the thrust.

If you are asking about the energy balance, the thrust from the propeller is always less than the drag from the wheels. If it were more, this would be over-unity. Since there is more drag than thrust, energy must be continuously added into the system to maintain speed. Since the wind coming off the prop is at a higher speed rearwards than the cart it self, it maintains "contact" with the wind and allows the cart to move faster than the wind while being powered by the wind. Kind of like a virtual air sail if that helps.
 
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Dan O. said:
Humber, we need to both stay focused. Wining the wager is not the goal but the means of reaching the goal of finding the truth. When we complete this quest and one of us discovers how we had deluded ourself, the $100 donation will be a small price to pay for the knowledge we will have gained.

As we proceed, we need to insure that there are no misunderstandings. If a statement is not understood, ask for clarification. Only when we mutually agree on all the parameters of the test will the results be mutually accepted.

I believe we could both accept the results of a properly conducted outdoor test on solid ground and with real wind. But there are many variables in that test that cannot be controlled. If you ever watched a field of long grass in the wind you would know that the wind is never constant. There will be shifts in the wind that make determination of "down wind" indeterminate and there will be rolls and gusts that make the speed of the wind indeterminate. Even waiting for acceptable wind conditions makes the testing time indeterminate. These factors may preclude convincing JREF to facilitate this test so it would be to our mutual benefit to find a controlled indoor test that is satisfactory.
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Yes, I agree. I said 'wind' , on the understanding that we were looking for an indoor solution, so 'airflow' is perhaps the term I should have used.
The treadmill can only provide wheel drive, so I am wondering, how?
 
Humber, the prop is always driven by the wheels. As soon as the cart starts to move, the gearing between the wheels and the prop forces the prop to turn. As the speed of the cart increases, the prop spins faster, still linked to and powered by the wheels. When the cart reaches windspeed, the wheels are powering the prop. The air is still but the prop pushes against that still air - and the ground moving under the wheels powers the wheels, which powers the prop.

When the cart is outside, the wind pushes the cart forward. The forward motion drives the wheels which turns the prop. The wind provides the energy to turn the wheels by forcing the cart to move across the ground.

When the cart is on the treadmill, the wheels are powered directly by the treadmill.
 
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humber said:
There is no real need for the cart to move. As long as there is a tail wind, then a true "treadmill", that is, a moving road that neither takes nor supplies energy, can be employed.
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When the cart is stationary on solid ground and a wind is hitting the propeller, the lateral and rotational forces exerted on the propeller will be translated to forces exerted on the road by the wheels. As soon as the cart starts rolling, the force exerted on the road over the distance the cart travels is energy. Can you say that the road is not taking nor supplying this energy?


Starting from a tether would make life easier. I assume that the test is to be monitored, so that should not raise questions of cheating.
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I would expect the arbiter to setup and perform the test so there is no access to rig the results by anyone with a stake in the outcome.


Do you have problems with Ynot's idea?
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Ynot has had many ideas. One that I like is the guide wire running the length of the treadmill. It controls the horizontal positioning of the cart with minimum interference in the direction of travel.
 
ynot, I *knew* there was a reason I liked you and just couldn't put my finger on it. I now understand.

You're a curious man. Good on you. Let me know if there is anything I can help with.

JB

ynot said:
Just had this brief conversation with my son . . .

Son - “So you’re going to spend time and money building this thing that you’re fairly sure won’t work?”

Me - “Yes”

Son - “And even if it does work it doesn’t have any practicle use?”

Me - “Yes”

Son - “ Are you sure you’re my father?”

Me - “Ask your mother.”
Click to expand...
 
Has anyone else noticed that approximately 40 pages of this 41 page thread are dedicated to trying to teach basic physics to humber?
 
spork said:
Has anyone else noticed that approximately 40 pages of this 41 page thread are dedicated to trying to teach basic physics to humber?
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And you would advertise that you only just noticed that?
Where would you be without me.
There is still the question of the denied or rejected proposals to meet your wager. Please inform.
 
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