Down wind faster than the wind

[jjcote]

Okay, a good point. Given a sufficiently large "sail", you can generate a huge amount of downwind force at a speed very close to wind speed. However, as I understand it, as the speed approaches the wind speed, the force is going to be reduced until it matches the resistance.

Having made the point, I'll now completely waffle on it. There's nothing incorrect in what you wrote that I just quoted, although there there is a bit of vague wording.

I wrote up a more detailed explanation of this, but it was a verbal jumble that I'm not happy with, so maybe I'll get back to it later, need to wrap presents and pack right now.

 

[jjcote]

They have the characteristic of being orientated "to a fixed point in space".

No. Such. Thing.

Yes, but even a bubble, a vert low drag from, cannot reach windspeed in a constant wind.

Really? What would possibly stop it from doing so? Strange that you word it this way, since a sphere is not a particularly low-drag shape (although a bubble does have zero rolling resistance along the ground), and the higher the aerodynamic drag, the more quickly it will reach wind speed!

 

[jjcote]

But if that power is used to drive the wheels faster the best that can be hoped for is that speed that was lost by the addition of the power extraction device can be regained if everything works at 100% efficiency and without friction losses.

The critical point here is that the power available from the wind as you load up the axle has nothing to do with the kinetic energy of the cart. It's not that the cart is coasting and you're pulling some energy out of its motion. The wind is still there to keep it up to speed even as your generator is pulling energy out of it. You can have a steady-state situation ("terminal velocity" if you prefer) at something a bit lower than windspeed where the generator is putting out constant power, but the cart speed is not changing. This power is not coming from the slowing of the cart, it's coming from the wind driving it. With a lightweight cart and a big sail, the power available can utterly dwarf what you could get from bleeding speed off of the cart. And conversely, that power can be used to accelerate the cart dramatically. The cart won't continue to accelerate, because the power will get sucked up by rolling resistance, and eventually, aerodynamic drag.

The magic of the prop is this: a propeller is a device that you can spin (which takes some power), and when it's spinning, it behaves just like a flat disk that's moving backward through the air (although it doesn't actually go anywhere). A prop in still air therefore provides a forward force, just like a disk moving backward through the air would. If the prop is actually moving forward through the air, that cancels out its "virtual" rearward motion, and at some speed it provides no force. (This is important: a spinning prop in a headwind does not provide a rearward force until it the headwind is faster than the advance speed of the prop.) So when you have the spinning prop on the cart that's driven by the axle, and the cart is at about wind speed, you get a forward force out of the prop. It takes some power to spin the prop, but you have power available from the axle. Once the cart is moving at faster than wind speed, it doesn't take any power to keep the cart moving at that speed (beyond rolling resistance and some modest aerodynamic drag), it just takes power to spin the prop, but the prop may well still be providing a forward force.

(This is more verbal stew, not much better than what I wrote earlier and discarded. It's all correct, but I think it may be from from clear and more confusing than it is helpful...)

 

[humber]

I just can't believe the sheer quantity and quality of gibberish humber is spewing. I fear he's about to blow.

We're now at 70 pages of humber's in-depth pseudo-scientific analysis, and he has yet to suggest a single experiment or prediction. He has yet to even offer ONE of the things he's promised (such as a proof that the treadmill test is not valid).

humber, I challenge you to make one rational statement - ONE. It doesn't even have to be of a scientific nature. But it can't ramble on with a bunch of terms thrown together to yield absolutely no meaning.

Just one coherent statement. Prove to us you can do that.

I have several times, but on each occasion, you find a reason not to do them.
It's not just my ideas, but those of others. The only videos you make, are to malign your detractors or to show that you are not cheating.
When there is something, say Y'not's idea, you leave it to him. Too buy, not possible, but there seems to be time to make mare self-serbing videos, and track down Bauer. .
When I suggest that you do the load test, you post the original video, saying "I just made-ed it" So, you have not done as you say, so your offer is empty and I can't be bothered to fill it.

 

[ThinAirDesigns]

When I suggest that you do the load test, you post the original video, saying "I just made-ed it" So, you have not done as you say, so your offer is empty and I can't be bothered to fill it.

Wrong Humber -- we did *exactly* as you asked ... we put 'sufficient weight on the axle as to keep the drive wheels from slipping' and recorded the results.

We did *your* test to *your* specifications. You want a different test, define one.

JB

 

[Marcus]

Wrong Humber -- we did *exactly* as you asked ... we put 'sufficient weight on the axle as to keep the drive wheels from slipping' and recorded the results.

We did *your* test to *your* specifications. You want a different test, define one.

JB

But but but slipping doesn't matter, don't you dare mention it, I will put you on fast scroll.

There was the test that had you replacing the prop with a flywheel, but Humber backed out of that one, too, saying that the cart could go backwards, just not as fast as the belt. Thus making his prediction unfalsifiable, as any wheeled object would do this.

 

[John Freestone]

Whoops, sorry about #2795, spork - that was a humber quote, but somehow ended up with your tag on it. Not too difficult to tell you apart, thankfully. My edit button's expired now.

 

[humber]

No. Such. Thing.

Ahh..a religious man. So sure of his beliefs that he does not check and assumes that all critics must be converted to your thinking.
But here, you are flat out wrong.
http://en.wikipedia.org/wiki/Gyrocompass
There is no such thing as "Centre of Gravity", it is notional. "Fixed point in space" is used notionally when talking of gyro compasses." Not heard of The Great Attractor?
Whatever, a gyrocompass will tell me all I need to know. Mythbusted.

Really? What would possibly stop it from doing so? Strange that you word it this way, since a sphere is not a particularly low-drag shape (although a bubble does have zero rolling resistance along the ground), and the higher the aerodynamic drag, the more quickly it will reach wind speed!

Check your text books.

 

[Dan O.]

No. Such. Thing.


Really? What would possibly stop it from doing so? Strange that you word it this way, since a sphere is not a particularly low-drag shape (although a bubble does have zero rolling resistance along the ground), and the higher the aerodynamic drag, the more quickly it will reach wind speed!

He is probably ignoring the reality of there being real and practical limits to measuring the speed of the wind and bubble and assumes acceleration of the bubble to wind speed will be a decaying exponential that approaches but never reaches the speed of the wind.

However, you also need to consider that if the system Q is greater than 1/2, the bubble will actually pass wind speed and subsequently oscillate around the speed of the wind as it settles down to traveling with the wind.

 

[humber]

Wrong Humber -- we did *exactly* as you asked ... we put 'sufficient weight on the axle as to keep the drive wheels from slipping' and recorded the results.

We did *your* test to *your* specifications. You want a different test, define one.

JB

Point to the video and timestamp.

 

[humber]

But but but slipping doesn't matter, don't you dare mention it, I will put you on fast scroll.

There was the test that had you replacing the prop with a flywheel, but Humber backed out of that one, too, saying that the cart could go backwards, just not as fast as the belt. Thus making his prediction unfalsifiable, as any wheeled object would do this.

No he didn't. You have nothing to say.

 

[humber]

He is probably ignoring the reality of there being real and practical limits to measuring the speed of the wind and bubble and assumes acceleration of the bubble to wind speed will be a decaying exponential that approaches but never reaches the speed of the wind.

However, you also need to consider that if the system Q is greater than 1/2, the bubble will actually pass wind speed and subsequently oscillate around the speed of the wind as it settles down to traveling with the wind.

(1)Hopeless attempt a parody.
(2)Also, technically wrong.
(3)Oh, you didn't mention the first point that a gyroscope can inform me.

Three strikes.

 

[John Freestone]

Tiresome.

If you're tired, STFU.

The same experiment same load, same skates, will produce the opposite effect upon the treadmill.

Does not compute. Someone suggested skates on ice for a good reason, because they have low friction. "Same experiment..." therefore, would require a treadmill surface with ice-like friction. They aren't usually like that, but it's not beyond imagining. So we have a person pulled by a parachute by the wind on a completely slippery treadmill. No, there will be no "opposite effect on the treadmill".

Wheels confuse you, John.

That's rich coming from you. If you want to insult my intelligence concerning wheels (which, by the way, were not even part of the scenario I used), at least first have the courtesy to answer my questions about bullets, being sucked into propellers, or the difference or sameness of the KE of a body at rest at the poles and equator.

Make it a flat piece of wood, on say, a waxed floor. Now try.

Make it my foot on, say, your arse.

(1) In case the real world, max velocity and forces as claimed.

(2) Treadmill maximum velocity ( ie still on belt) is when those forces are at a minimum. Now, take a deep breath. At all other times, the cart will go backwards down the belt (at some speed)


(3) Winspeed is only achieved when the forces are minimum.

You would not even pass the Turing test.

 

[CORed]

You think know a lot about what you have not seen. I observed it out of interest. I worked in an orchard after school. I have curiosity.

Unfortunately, not the knowledge or intelligence to correctly interpret what you have seen.

For cleanliness, the floor of the belt is flat stainless steel. Alos, if rolled is will resume its activity elsewhere.

Consistent either with an inclined belt or a weight induced sag in the belt.

The belt is not inclined.

You checked that with a level? It wouldn't take much slope to cause that effect.

They will do this for a long time, so that accretion rings form The orange is not a unique case, in fact quite common. Apples too. All the rest, wrong, wrong, wrong.

Okay, as I'm sure everybody but Humber understands, the oranges, apples, cherries are not going to remain stationary on the belt for more than a few seconds, unless some force is keeping them there. The most likely force is gravity, due either to an inclined belt or a weight induced sag in the belt.

Cherries can climb perhaps a foot up an apparently smooth and motionless inclined plane. How do you think they do that? Oh, I forgot.

Well either the cherries were already in motion when they started up that inclined plane and they rolled up on momentum, or there were some really good drugs being used in that orchard, which, now that I think about it, would explain a whole lot.

No belt sag required. Wow, he almost thought it...low resistance.

Actually, that would have to zero resistance. Possible only in the Humberverse.

though it does show that you are willing to accept any thing that stays on the belt as being windspeed. Can I sell you som real estate? You make up both our minds, OK? You build one, but mind the sharps.

This is so incoherent I won't even attempt to refute it. It's self refuting.

Risible. You are using "feels like" as an instrument. Folk physics. (51%, remember). Wow! tragic error.

Yes. Yours.

It's the fact that the forces are not only equal but opposite, but maximised.

Only in the Humberverse.

Forces are maximised not minimised at terminal velocity. I put a gauge in the skates, so that you wouldn't fall into your own trap. Oh, boy, Spork has it easy!

Repeat that as many times as you like. It's still wrong.

Actually they are roller skates, ( hence wheels) but even so, why does the skater not continue to accelerate?

Well, you didn't specify in your earlier post, and I assumed ice skates. It really doesn't matter.
The skater doesn't continue to accelerate because when the parachute approaches wind speed, the force derived from the wind is reduced until it matches the friction of the skates.

Another schoolboy error. Make it an aircraft. Make it a car....

Yes, let's make it something completely different and pretend it's the same thing. However, if the airplane, car, horse or whatever is moving at a constant speed, the force will still decrease when the skater is close to the speed of the towing vehicle. If you can't understand this. You're hopeless. But we already know that.

And no, parachutes do not behave like that. They can be designed to be like a 'constant' force or 'constant' velocity.

Parachutes are magic in the Humberverse.

You say, that forces are mimimum at terminal velocity. All your arguments are either based upon that false assumption, or other matters equally so.

Your alleged refutation of the equivalence of the treadmill and the "real world" rests on you incorrect assumption that the forces are mazimized at "terminal velocity" in the "real world" but not on the treadmill. Okay, Humber, the skates have very low friction. Why doesn't the skater continue to accelerate when the parachute is close to wind speed. Better, since you think parachutes are magic, make it a sail. I'm waiting. I'm sure it will be outrageously funny.
[/quote]
QED. You have embarrassed yourself. But you must enjoy it, because you keep doing it.

 

[humber]

The critical point here is that the power available from the wind as you load up the axle has nothing to do with the kinetic energy of the cart.

The apparent mass affects the acceleration and the amount of stored KE.

It's not that the cart is coasting and you're pulling some energy out of its motion. The wind is still there to keep it up to speed even as your generator is pulling energy out of it.

Depends upon the amount of available energy, and the load that the generator represents. If you always know one is greater, then there is no problem, but then again no dispute over the possibility.

You can have a steady-state situation ("terminal velocity" if you prefer) at something a bit lower than windspeed where the generator is putting out constant power, but the cart speed is not changing. This power is not coming from the slowing of the cart, it's coming from the wind driving it.

If the cart can get to that position is does not need the generator.

With a lightweight cart and a big sail, the power available can utterly dwarf what you could get from bleeding speed off of the cart. And conversely, that power can be used to accelerate the cart dramatically. The cart won't continue to accelerate, because the power will get sucked up by rolling resistance, and eventually, aerodynamic drag.

Storage is time displacement. The two situations need not coincide. Still, nothing to be claimed. Any number of designs could do the same.

The magic of the prop is this: a propeller is a device that you can spin (which takes some power), and when it's spinning, it behaves just like a flat disk that's moving backward through the air (although it doesn't actually go anywhere).

It moves forward.

A prop in still air therefore provides a forward force, just like a disk moving backward through the air would. If the prop is actually moving forward through the air, that cancels out its "virtual" rearward motion, and at some speed it provides no force. (This is important: a spinning prop in a headwind does not provide a rearward force until it the headwind is faster than the advance speed of the prop.) So when you have the spinning prop on the cart that's driven by the axle, and the cart is at about wind speed, you get a forward force out of the prop.

You need a source of energy to do that. Momentum will do.

It takes some power to spin the prop, but you have power available from the axle. Once the cart is moving at faster than wind speed, it doesn't take any power to keep the cart moving at that speed (beyond rolling resistance and some modest aerodynamic drag), it just takes power to spin the prop, but the prop may well still be providing a forward force.

Circular. The prop drives the wheel drives the prop.

(This is more verbal stew, not much better than what I wrote earlier and discarded. It's all correct, but I think it may be from from clear and more confusing than it is helpful...)

Overcooked.

 

[spork]

Whoops, sorry about #2795, spork - that was a humber quote, but somehow ended up with your tag on it. Not too difficult to tell you apart, thankfully. My edit button's expired now.

No worries. When I first saw it I thought about taking a contract out on your life - but then I realized no one could possibly mistake my words for humber's or vice-versa.

How's that one coherent statement coming along humber? Just one sentence that holds together. It doesn't have to be about this cart or DDWFTTW, or even technical. It could be "I have a dog". Give it a try. Let's find a starting point - if you can.

 

[spork]

You would not even pass the Turing test.

Best comment of the thread. I wish I had more room in my sig to add that one!

 

[John Freestone]

CORed, I'm pretty much with you on everything you've said, and I know you will know most of the following, but I just wanted to say that I don't think there's any need for a dip or slope in the conveyor belt in humber's orchard, or the supermarket checkout, for a roughly spherical object to rotate and remain approximately at the same position on it for some time. It's a red cherry - I mean, herring - like everything else humber has said for the last 70 pages. He is so untrained in Newton's laws that he does not realise that a body at rest will remain so unless a force is applied, or he can't figure out any rudimentary things from that law and the way balls, oranges, marbles or wheels behave under tangential forces applied to their circumference.

To most people over 3 years it is probably fairly obvious that if you put some oranges on a tablecloth on a flat table, and then tug the tablecloth, the oranges will tend to rotate and stay roughly where they were, following a little.

If a pool table were made to accelerate swiftly, the balls would all remain approximately at their original positions w.r.t. the room, until a cushion hit them, and there's not much in the way of dips or slopes on pool tables if they're built right.

If your car was put on a vehicle transporter, unsecured with the brake off, and at that point another truck rear-ended the transporter, most of us would not be surprised if the car fell off the back, rather than moving forward with the transporter. Humber would obviously be transfixed by such amazing magical effects.

Of course, for relative novices like myself, there are interesting questions that we could discuss, about how the force acts on a sphere or wheel to both give it angular momentum and how some of that ends up accelerating the centre of gravity as well. This last part is why, of course, the orange, pool balls, cherries, 'un-prop-ed' cart, or indeed ynot's glass marble on a turntable, etc., do not manage to keep up. Some guys round here, I'm farily sure, would be able to tell us how the force is translated into rotation vs acceleration with the surface.

Of course, a dip, or a slope, can cause some of the weight to be added to the forces, making the objects actually not move laterally, but just rotate. The cart, with its prop removed, falls off the back of the treadmill. A slope forward could balance the tread's force (aft) with a component of the weight (forward). The opposite slope is required to keep the cart with its prop 'balanced', showing that it is making headway against the tread, that forward force being derived, of course, from the prop.

One other addition to what you said, those cherries might not only climb a slope because they already have (lateral) velocity in the up-slope direction, but because they have angular momentum, or a combination. Again, anyone who has put spin on a ball knows that it can be made to translate this angular momentum into lateral motion.

His questioning why these things happen is only to suggest that he has a clever insight into why the cart doesn't work the way everyone else knows it does, but actually just demonstrates either his extreme ignorance of the physical world (not even 'physics' - small children could out-predict his understanding of it), his deliberate pretense not to understand (i.e. pure trolling), or both. I think Dan O's recent analysis is right - humber started off convinced he had some special insight into why it didn't work, and he's been avoiding facing up to that error ever since, digging a deeper and deeper pit of partially feigned stupidity.

 

[John Freestone]

Best comment of the thread. I wish I had more room in my sig to add that one!

It's good isn't it? I only wish I'd thought of it - I nicked it from somewhere else on the forum.

 

[Dan O.]

Don't get mad, use it. F=ma+d: the force pulling the skater is the product of the skaters mass times the acceleration plus the drag from the skates. The pull of the parachute can be calculated approximately by F = 1/2 * p * V^2 * S * Cd Where: Cd=Coefficient of Drag (approx. .8 to 1.0); p(or rho)=Air Density; V= Velocity, S = surface area of parachute (or for simplicity, F is proportional to V^2). The drag due to friction of the skate on ice is pretty close to d = Cf*m*V where Cf for a steal skate on ice can be as low as 0.005 (but depends on temperature, blade geometry and the ice roughness) and m is again the mass of the skater (note that V here is the velocity of the skater relative to the ice where V in the force of the parachute is velocity of the air relative to the chute.