Down wind faster than the wind

[sol invictus]

This is really too good to let go. You missed the point at least twice.
Dan_O's questions are always loaded, you see. Notice that? Simple arithmetic, for someone in "my field".

Whatever.

ROLF

The floor is laughing?

The analog of voltage is velocity. What happens when you apply the same velocity 'across' an object. Ohh nothing it the same humber oh the same!!
You forgot that like voltages, forces can be common-mode. Any differences becomes a 'frame' eh?

No one said anything about forces being relative, humber.

Anyway, now that you agree my cart/radar/buffer means that I can be quite certain that the cart is moving wrt the ground, and that I can measure the resultant KE, you cannot apply your counter-argument to the treadmill.

Gibberish.

According to Galileo, Newton, Einstein, and every other physicist over the last 400 years, the treadmill experiment proves (up to finite-size effects, which you've never even mentioned) that the cart will go DDWFFTW. There's just nothing more to say.

 

[humber]

Whoa, whoa, whoa, WHAT?! There may be a far more basic lack of understanding going on that I had realized. You think that there's a headwind? What in the world is indicating a headwind to you? I have a notion that you have a total misconception of what the treadmill is being used for.

No. Remember one thing. Nothing about the treadmill is what it is said to be.
'Tailwind' and 'headwind' are used in this thread as is it were so.
There is viscous drag between the belt and the air. From the perspective of the cart, that is a headwind. It 'blows' from the front of the cart. The cart is said to have a tailwind, so the profile magically goes from headwind to tailwind? The paper even shows a (slight) headwind even at prop height.
See how vigorously the paper moves when close to the surface? Do you think that may create some lift around the wheels? Quite lot of mass, at considerable velocity, right there.

Are you under the impression that the treadmill is being used in an attempt to move the air in the room around? That it's some kind of inefficient linear fan or something? That isn't what's going on. The air in the room is assumed to be totally still (and the streamer is used to test that). For the purposes of the test, the only things that matter are the air and the surface of the belt, because those are the only things that the cart interacts with once the hand lets go of it.

Well, no, but as has been earlier noted, a fan would be more efficient. The treadmill is false, and this is yet another indicator.
The belt is the road, not the wind. Yes, the air should be totally still, you are right there. Even if that is ignored, and the belt-wind seen as equivalent to the laminar flow over a real road, it is still going the wrong way. That is never a headwind in the real world. It is not correct at the bolthole of precisely 'windspeed' either, because it remains exactly as it is, even if the cart goes backwards (less than windspeed). It is spurious.

From the perspective of the camera, an object sitting on the belt moves to the left, and thus feels a wind from the left (a tailwind). The cart is moving forward on the belt (toward the right of the picture) as fast as that tailwind, so it's feeling no wind (just as an object on the road moving at windspeed feels no wind). Do you have some different misconception of what's going on here?

That's the sales pitch, but then, why then is there no reaction when it slows, goes backwards? Notice something about the motion, particularity in #7. It slews in a circular motion. ( probably precession of the propellor). But once in a pattern, the acceleration is almost constant. It does not respond to immediate stimulus. You have the answer in your reply to CORed.

 

[humber]

Whatever.



The floor is laughing?



No one said anything about forces being relative, humber.



Gibberish.

According to Galileo, Newton, Einstein, and every other physicist over the last 400 years, the treadmill experiment proves (up to finite-size effects, which you've never even mentioned) that the cart will go DDWFFTW. There's just nothing more to say.

Nah. Your response is too limited, to muted, for the tenure of my post. Dan_0 has a cat for an avatar, but that's as far as it gets when playing cat and mouse.

You are in no position to tell me what any of the above would say, so it is appropriate tht you don't do so. You are right. The finite size is a log in the eye.

ETA:
I should say that you did, Sol
Absolute voltages are meaningless. Only voltage differences mean anything, just like velocities.

 

[humber]

Yo - be patient there JJ. humber is going to prove to us exactly why the treadmill has no relevance here. Just give him a chance. He's only been at it for 70 pages.

Once again, a bellow from the bleachers.

 

[fredriks]

Humber, your recent posts are even more ridiculous than usual. You clearly show in all your recent posts that you don't have a clue about the meaning of a reference frame.

I am impressed though that someone in your field think that U=R*I is simple arithmetic. I mean that level of algebra is probably teached to children 10 years old or something. I didn't believe that you had reached that level yet.

 

[humber]

Are you aware that when you step onto a moving belt, you are no longer in the same inertial frame that you started in? The reference is not allowed to accelerate.

OK, but you do accept that is is no more than walking faster? So why does being in a new frame make any difference. You know that equivalance will not allow any differences to exist. But you don't need some warmed-over first year ideas to tell you that. You know that things are the same from all perspectives. Equivalency is not a magic wand, it just formalizes the idea, so that you can say formally that you can't make a difference. It was once though that you could. Some take the ideas that because you can't as the basis of a redundant hypothesis.

The accelerometer can't tell you what frame is "stationary". If you step from the ground onto a moving belt it will give you a result, but if you step from a belt moving the other way onto the ground it will give the same result.

You are being lured into a phony sort of relatively with this absolute/can't tell line.
Yes, but I need only know. JB says that I can't tell the wind of his porch on a belt from the real. If the wind on my real porch changes, I see no acceleration, but on JB's they are directly related. I can also use a gyroscope. They have the characteristic of being orientated "to a fixed point in space". The earth is also a gyroscope, so its axis of rotation is in alignment with an unfettered gyroscope. This allows absolute position on the earth to be determined. Common on ships.
Now I can say that I am moving relative to the ground, and in which direction, and that the wind is artificial, so Mythbusted.

If there are a bunch of treadmills (running a different speeds and directions) lined up in the gym and you keep stepping from belt to belt, working your way across the room, you can't tell from the accelerometer when you have reached a belt that's turned off unless you know what the belt you started on was doing.

Yes, I have often wondered why there is no cyclone at the gym. Again, I need only be alerted once. When that occurs, my direct senses fix the cart to groundspeed. Then, all the measured anomalies, apparent winds, lack KE, become seen for what they are. Not "explanations" of the model, but everyday facts about things. I cannot be fooled, unless I am starved of ALL the information that can tell me otherwise.

This leads to another point. I am told there is really a wind, I can't tell that it from the real thing, but my accelerometer and other devices tell me otherwise. It is backwards.
Now that I know the truth, I can definitely build a cart that operates under those conditions, and stays on the belt just like the cart, yet it is universally acknowledged not to be capable of reaching windspeed.

So what do you say to that?

 

[humber]

Humber, your recent posts are even more ridiculous than usual. You clearly show in all your recent posts that you don't have a clue about the meaning of a reference frame.

I am impressed though that someone in your field think that U=R*I is simple arithmetic. I mean that level of algebra is probably teached to children 10 years old or something. I didn't believe that you had reached that level yet.

I want to know if JJcote thinks I am being ridiculous.

 

[fredriks]

I want to know if JJcote thinks I am being ridiculous.

What have that to do with my post?

 

[humber]

I'm going to disagree with you on this, JJ. If the parachute is at windspeed, it can't supply any force. In order to produce a force, the parachute has to change the momentum of the air around it, and it can't do that when it is at the same speed as the air. Also, the higher the drag from the skates, the more force is required to overcome that, and the more the momentum of the affected air has to be changed to produce that force. That will result in a greater difference between the parachute speed and the air speed. A bigger parachute will increase the amount of force available and will get the system closer to the actual windspeed than a smaller parachute - but it will never quite be at rest with respect to the air.

That is around the point. Replace the parachute with a constant force, or controlled device that maintains a constant force. The result stands.
No matter what force is available, potentially available, the load will still determine the applied force it is lower that that potential.

That is a crucial point for anything powered by the wind. The amount of force available is calculated from the speed difference between the air and whatever the wind-powered device is anchored to. If the device happens to be moving but is linked to the ground, the force available is still calculated according to the difference in speed between the air and the ground. As the difference in speed between the device and the air gets larger, more energy can be harnessed from that speed difference.

If it happens to be linked to the ground, the difference between the device and ground is the same as the difference between local, impinging wind and ground.

If that amount of energy is higher than the drag of the device when it is at the same speed as the wind, the device will accelerate to a higher speed as long as it remains linked to the air and the ground in order to harness that force. When the forces balance, the speed will be constant.

Yes, but even a bubble, a vert low drag from, cannot reach windspeed in a constant wind. A cart is much higher drag, so it would need to be near 100% efficient to match a bubble.

Surprisingly, humber got the treadmill example correct and the real world example wrong, as you pointed out, JJ. I'm curious to see how he's going to wiggle out of this one. Likely something about the fact that we don't understand that minimum and maximum values of something are relative and since the treadmill and the real world aren't equivalent, he can show that either one can be used to illustrate his point.

No, I am quite correct. In wind, the final velocity is determined when the forces are a maximum. If you don't like the parachute, then we can discuss another device, but it will be in vain. In real wind, drag increases with velocity, and so does the KE. This is opposite of the case on the treadmill, where all devices are driven to a minimum, and a KE to zero.
If you think that drag falls because it is downwind, then free energy machines by lunchtime.

 

[humber]

I have no idea what you even mean by "contradicts the treadmill", and neither does anyone else. Personally I don't spend a lot of time arguing with non-sentient objects (except on this forum).



There.is.no.such.thing.as.100%. Any amount of energy can be released, from zero to infinity. The energy released depends on the relative velocity, which means if you change the velocity of the "buffer" while leaving the object alone, you change the amount of energy released. That's why your definition is nonsense - KE is not an intrinsic property, it's a frame-dependent quantity (or if one tried to use your definition, buffer-dependent).

I only need show that velocity wrt the ground demands an increase over a stationary body. The treadmill says, and you say, that KE is relative, so the treadmill is cool. No its lack of KE means that it is not travelling wrt the ground as claimed.
That was the point. I asked for a real world object that travels at speed or velocity wrt the ground, that does not increase its KE in the process.
That you have not done, and acknowledge that in post #2748.

 

[humber]

Hello all. I have been reading with delight humberisms in this thread but it seems like everyone missed this one:



He did not keep this up but it seems that even using the Earth as a frame of reference was not good enough for humber. Well if he does not get the Nobel Prize for his brilliant arguing here he will definitely get it when he finds the center of the universe.

Yes, was using Socratic irony to show those forces to be arbitrary assigned.

On a sad but serious note his arrogance, thickheadedness, and misuse of terms that he thinks he understands reminds me of a girl I knew who had a meth addiction. When she was under the influence she had delusions of grandeur and an attitude that matches humber. She would also try to use terms that she did not understand and if you listened to her she almost seemed to make sense sometimes.

Whereas you don't need meth. to display the same characteristics. Your remarks a self-serving appeal to herd morality and sensibilities.

A quick note about me I was on the anti side on the Mythbusters' forum until spork and JB made their first video. Then I was one of the first to congratulate them and own up to my mistake. Unlike humber I recognize a valid frame of reference when I see one.

Do be quick. No that means that the original reason for your denial was a knee-jerk reaction. When something appeared to contradict that, you bought it. To reconcile that difference, you told yourself how clever you really are, and then waved an apology to prove it. Your failures, then becoming a badge of honour. Neat, huh?

Not one single physics-related rebuttal in your entire post.

 

[humber]

I have also been waiting all day for humber's proof that the treadmill is not a valid frame of reference. It seemed he was going to do some sor of demonstration as shown by this statement to spork:

Well, got a bit sidetracked disusing that very same matter. I have demonstrated that I can tell belt world from real world, so perhaps you can digest that first. Don't forget the self-flagellating apology,

Oh well, just another unfulfilled promise from humber.

I doubt that you will ever fulfill your promise.

 

[humber]

What have that to do with my post?

It means that I am fussy about who's opinions count.

 

[Dan O.]

Thought experiment:
If the power obtained from the rotation of the axle is used to power a mass chucker (100% efficient ion cannon, rail gun, etc.) instead of the propeller would the cart exceed the down wind speed?

Even assuming 100% efficiency, I suspect that the answer is no.

Your suspicion is wrong. The energy required to eject a 1 kg mass at 1 m/s relative to the cart is (E=1/2 mv^2) 1/2 watt. This will produce 1 newton-second of thrust. A generator extracting 1 watt for 1 second from the forward motion of the cart at 1 m/s through the axle will create a breaking force of 1 newton (E=F•d). This looks like free energy. But where does the ejected mass come from?

If you had the mass on board, you are simply trading the carts momentum for energy 1 kg at a time. If you try to pick up the 1 kg mass from the track, you loose more momentum accelerating the mass up to the cart's speed. But if you are fortunate enough to have a separate stream of 1 kg masses traveling at the speed of the cart, you could just pluck one out of the air (so to speak) at no cost in terms of energy or momentum.


[side note: ion thrusters are efficient not in terms of energy expended but for thrust generated per unit of mass ejected]

 

[John Freestone]

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

QED. You have embarrassed yourself.

Spork says, jjcote says, CORed says, Newton says, I say.

What is terminal velocity? Don't even get clever (like there'a a risk). Just simple description - it is a steady, unchanging velocity. There is no acceleration. Now, your assertion that there is a balance of equal and opposite forces is true. It is the general case. But those forces can be very large, say with an ice-pick stuck in the ice, or very small, gliding smoothly along in the wind.

Not only are they right and you wrong, but if it were possible to reduce the friction to zero and have a perfect, weightless parachute, etc., the skater would accelerate to terminal velocity, travelling at exactly windspeed, and the horizontal forces would reduce as usual to a minimum - this time, zero. Skater and chute would glide along in uniform motion without a force being applied. Analogue: a piece of debris, the same density as a fluid, picked up by the fluid ends up moving along with the fluid without any forces at play.

Yes, simply another 'terminal' fail by Humber to understand Newtonian principles.

 

[humber]

It seems like some people here understand what is going on better than I do. I have been trying to work it out for a few days without success. So I'd like to talk about it a bit.

First. I believe the source of power for the device is derived from the rotation of the axle the wheels are on. I was happy with that as the total explanation for awhile, but then I got to thinking about that.

The power comes from the belt via the wheels when on the treadmill, but from the propellor when in the wind.

If a device derives energy from the rotation of the axle, the axle will be slowed. And thus the cart will be slowed per force to less than the wind speed if the power is just dissipated away in a way other than making the cart go faster.
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.

Not fromthe axle. The wheel is transmission device, not unlike your foot. It is a moving point of friction. We use them because they are efficient at doing that.

The obviousness of this idea is, I think, what makes the DWFTTW cart seem at first implausible.
But clearly the propeller makes the situation much more complex. The propeller adds drag so while the cart is going slower than the wind the propeller increases the amount of power available to the generator attached to the axle. This seems like what mender was alluding to above.
Cool, but so far all we've got is the idea that a bigger spinnaker can make the cart go downwind faster but not faster than the wind.

But the propeller is complicated because it is also providing thrust but if that was all that was going on we still couldn't go faster than the wind because the drag that was helping overcome the power sucked up by the generator attached to the wheels can't produce any power when the cart gets to wind speed to provide power for the thrust device.

The propeller cannot extract enough energy from the wind to overcome the forces that are generated against it during that process.

And the thrust produced by the propeller can not produce more power than can be extracted by the generator (see thought experiment below). So the result of the power balance where the thrust produced is constrained by the amount of power extracted from the rotation of the axle is that the cart can't go faster than the wind.

Yes, but from the wind and not the axle. The propeller generally absorbs energy from the wind, but sometimes the motion of the cart can drive the propellor. The momentum of the body alone, can through the wheels, drive the propellor to produce thrust. A bit redundant, because that is lossier than doing nothing.
Imagine though, that you can store more energy in the good times so that you may use it in leaner, less windy periods. Storing that as momentum in the propellor is one means of doing that. It may not get you that far, but can at least on average, it may make up for the losses of the previous situation. Not a killer perhaps, but better.

So the total answer seems to involve understanding the complex behavior of the propeller with respect to all this. I think the answer is related to what I thought the solution was in the first place. The propeller changes the air flow in front of itself enough that the apparent down wind speed the cart sees is somewhat faster than the actual down wind speed.

The complexity is snow.

There are confounding factors that make it difficult for a person with my level of understanding to predict what would happen right around the transition to greater that down wind speed.

If it gets there, then examination of how it does that, will inform of what happens after windspeed.

As the cart speeds up there is more power available from the generator. With a low friction, lightweight cart a speed very close to the down wind speed will be obtained even if a small load is added to the axle. So when the cart is moving very close to the down wind speed there's going to be a significant power source available. If that power can be used for thrust, the cart will go faster but as the cart exceeds wind speed it seems like that power won't be available, unless there is some magic in the propeller (and I think there is).

Yes, you would need more power than is available.

I'm sure that people have posted very good descriptions of what is going on here that address my confusion. The problem is that I couldn't easily easily find those descriptions buried in the 60 odd pages of this thread. Any references to the previous posts will be appreciated.

A lot of this thread is obfuscation.

Thought experiment:
If the power obtained from the rotation of the axle is used to power a mass chucker (100% efficient ion cannon, rail gun, etc.) instead of the propeller would the cart exceed the down wind speed?
Even assuming 100% efficiency, I suspect that the answer is no.

Like a pig-thrower used to clean oil pipes? Same rules apply. The axle and propeller are just part of the machine. A difference of technology.

As an aside, I've been very impressed with the videos and demos of spork and others, but if they'd really like to impress me I'd like to see the ion cannon experiment done next. Thank you in advance.

You may well imagine that I don't agree that the evidence is good.

 

[John Freestone]

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

Is that when they're trying to get out of a pan?

 

[humber]

Spork says, jjcote says, CORed says, Newton says, I say.

What is terminal velocity? Don't even get clever (like there'a a risk). Just simple description - it is a steady, unchanging velocity. There is no acceleration. Now, your assertion that there is a balance of equal and opposite forces is true. It is the general case. But those forces can be very large, say with an ice-pick stuck in the ice, or very small, gliding smoothly along in the wind.

Not only are they right and you wrong, but if it were possible to reduce the friction to zero and have a perfect, weightless parachute, etc., the skater would accelerate to terminal velocity, travelling at exactly windspeed, and the horizontal forces would reduce as usual to a minimum - this time, zero. Skater and chute would glide along in uniform motion without a force being applied. Analogue: a piece of debris, the same density as a fluid, picked up by the fluid ends up moving along with the fluid without any forces at play.

Yes, simply another 'terminal' fail by Humber to understand Newtonian principles.

Tiresome. The same experiment same load, same skates, will produce the opposite effect upon the treadmill.
Wheels confuse you, John. Make it a flat piece of wood, on say, a waxed floor. Now try.

(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.

 

[humber]

Not lost your cherry, John?

 

[spork]

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.