Merged DDWFTTW in a “Real” Wind

[jduffy77]

First of all, show me a frame of reference where the air is at rest, outside in the real world. Winds don’t move over the ground in response to the motion of the earth’s surface as happens on a treadmill. If you think they do, how would you explain the tornados that just tore through much of the South? Was the surface of the earth spinning wildly around in many different places, causing those wind funnels? You see, you can take these batty reference frame transformations too far, and arrive at all sorts of incorrect conclusions. You may as well stand on your head and call the floor the ceiling, and now your head is touching it. Little kiddies do that sort of thing and we think it’s cute. When grown men do that sort of thing, we call them crackpots.

As I said in response to another poster, you can say a sail cart or a wind turbine is powered by the ground, if it makes you feel somehow superior to say such a thing. But the reality is the planet earth is a large rock with a mass of about 6 x 10^24 kg, more than one million times the mass of the entire atmosphere. Due to gravitational attraction, the atmosphere moves with the planet, with the exception of local disturbances mostly due to temperature differentials and these are what we call winds. The winds are for the most part unpredictable, changing velocity and direction pretty much with a mind of their own, while this big rock we call the earth stays rock solid under our feet, regardless of how it moves through space. Objects sit still on the surface of this big rock due to gravitational attraction and friction with the surface, and it requires energy to move them. It is ridiculous to say that the energy to move them against the friction and gravitational attraction comes from the earth itself, the very thing that is holding things in place! It is ridiculous to say that a road, fixed on the earth’s surface, is going to power something to move along that road, because it most certainly does not do that!

Once again, if you want to act that that little boy, standing on his head and saying his head is now on the ceiling, go right ahead and do so. But you will probably find more than a few people laughing at you.

The kinematic energy for the sail cart is coming from that thing that is filling those sails, the wind and not from the ground. Changing the reference frame does not change reality, only your perception of reality. If your claim for DDWFTTW rests on a change in perception, as it appears it does, then it rests on nothing but nonsense and is probably not even worth discussing.

If you want to continue, then show me some mathematics to support this claim.

Why? Your own math has already shown to anyone who looks at it that the cart must work.

 

[Modified]

First of all, show me a frame of reference where the air is at rest, outside in the real world.

That's exactly why the treadmill is useful. It creates a nice, consistent, very steady wind, unlike most winds outdoors which swirl around and change direction.

Winds don’t move over the ground in response to the motion of the earth’s surface as happens on a treadmill.

What is causing the air to move relative to the surface is irrelevant.

 

[jadebox]

I know a lot of qualified people and I have already asked. Contrary to what you say, I have found no qualified physicist who believes the treadmill is the same as a road.

The equivalence of the frames of reference is, as someone recently said, basic physics. So, I doubt anyone who really understands frames of references would fail to see that the treadmill scenario is equivalent to the cart in the wind.

Perhaps you didn't explain the situation correctly. If you'll let us know the names of the "qualified people" you asked, I'm sure someone here will be happy to provide them with a better explanation.

-- Roger

 

[profpangloss]

Energy can be stored by pressurizing a gas in a cylinder. If I put a piston and cylinder with a gas in it between the two faces of a clamp-face a and b. One side of the clamp is attached to the earth, the other to a threaded screw attached to the earth. Now I don't tell you which side of the clamp is attached to earth and which side is attached to the threaded screw and I put pressure on the piston with the clamp. I can certainly rig my clamp so that both jaws move equally as I apply the pressure so no difference there.

Which is it Humber-Clamp face a or b putting the energy into compressing the gas in the cylinder? They both have the same pressure on each face by definition so which one is the energy coming from?[qimg]http://www.internationalskeptics.com/forums/imagehosting/thum_488654dc016c256936.png[/qimg]

The energy is coming from whomever or whatever is turning the screw.

 

[profpangloss]

That's exactly why the treadmill is useful. It creates a nice, consistent, very steady wind, unlike most winds outdoors which swirl around and change direction.



What is causing the air to move relative to the surface is irrelevant.

You agree the treadmill creates unnatural conditions that do not exist outdoors on the road. Thats a good start to understanding that it is not the same as a road. Good for you!

 

[profpangloss]

The equivalence of the frames of reference is, as someone recently said, basic physics. So, I doubt anyone who really understands frames of references would fail to see that the treadmill scenario is equivalent to the cart in the wind.

Perhaps you didn't explain the situation correctly. If you'll let us know the names of the "qualified people" you asked, I'm sure someone here will be happy to provide a better explanation.

-- Roger

Or perhaps you don't understand why the treadmill has no relation to a cart on a road? Yes I think that is so. Perhaps you should find some qualified physicist who agrees with your misinterpretation of basic physics, and post his name here.

 

[A.T.]

First of all, show me a frame of reference where the air is at rest, outside in the real world. Winds don’t move over the ground in response to the motion of the earth’s surface as happens on a treadmill. If you think they do, how would you explain the tornados that just tore through much of the South? Was the surface of the earth spinning wildly around in many different places, causing those wind funnels? You see, you can take these batty reference frame transformations too far, and arrive at all sorts of incorrect conclusions. You may as well stand on your head and call the floor the ceiling, and now your head is touching it. Little kiddies do that sort of thing and we think it’s cute. When grown men do that sort of thing, we call them crackpots.

As I said in response to another poster, you can say a sail cart or a wind turbine is powered by the ground, if it makes you feel somehow superior to say such a thing. But the reality is the planet earth is a large rock with a mass of about 6 x 10^24 kg, more than one million times the mass of the entire atmosphere. Due to gravitational attraction, the atmosphere moves with the planet, with the exception of local disturbances mostly due to temperature differentials and these are what we call winds. The winds are for the most part unpredictable, changing velocity and direction pretty much with a mind of their own, while this big rock we call the earth stays rock solid under our feet, regardless of how it moves through space. Objects sit still on the surface of this big rock due to gravitational attraction and friction with the surface, and it requires energy to move them. It is ridiculous to say that the energy to move them against the friction and gravitational attraction comes from the earth itself, the very thing that is holding things in place! It is ridiculous to say that a road, fixed on the earth’s surface, is going to power something to move along that road, because it most certainly does not do that!

Once again, if you want to act that that little boy, standing on his head and saying his head is now on the ceiling, go right ahead and do so. But you will probably find more than a few people laughing at you.

The kinematic energy for the sail cart is coming from that thing that is filling those sails, the wind and not from the ground. Changing the reference frame does not change reality, only your perception of reality. If your claim for DDWFTTW rests on a change in perception, as it appears it does, then it rests on nothing but nonsense and is probably not even worth discussing.

A lot of blather is needed to bury the fact that you can't answer Michael C's simple question.

If you want to continue, then show me some mathematics to support this claim.

If you want to continue, then show us some mathematics to support your claims. But first decide what your claims are. Currently you change them in each reply.

 

[A.T.]

Perhaps you should find some qualified physicist who agrees with your misinterpretation of basic physics, and post his name here.

http://blog.makezine.com/archive/2010/11/what-ive-learned-about-wind-carts.html

was even more convinced that DDWFTTW was real when I learned that Mark Drela, a world-renowned aerodynamicist at MIT, says it’s possible. Drela is the designer and maker of a variety of amazing human-powered, propeller-driven vehicles. In 1998, Drela designed a human-powered airplane called the Daedalus, which set a world record when it island-hopped more than 72 miles from Crete to Santorini.

Drela is also the developer of a computational aerodynamic analysis system called XFOIL, which allows aircraft designs to be tested before they’re built. An article in MIT’s Aero-Astro magazine reports that Drela has “engineered aircraft for Boeing, the wing for the Predator UAV, the keel of America’s Cup yachts, and experimental aircraft used by NASA. In addition to XFOIL, he has written design programs for rotorcraft, machinery blading, and axisymmetric bodies such as zeppelins.”

In other words, Drela knows his stuff. And so what does his analysis conclude?

“Although DDWFTTW seems like it violates physics, it really does not,” Drela explained to me via email. “The various analyses show this, and the cart experiments on YouTube are definitive proof. In my view, the most closely controlled and unambiguous DDWFTTW demo is the cart climbing up the tilted treadmill. The main problem is then convincing some people that this is equivalent to DDWFFTW. But whoever tries to argue against that equivalence is really arguing against Galilean relativity, which is unassailable. So that secondary argument is a complete waste of time.”

So Goodman, Andrews, and Cavallaro have been vindicated. DDWFTTW is possible.

 

[Jack by the hedge]

If your claim for DDWFTTW rests on a change in perception, as it appears it does, then it rests on nothing but nonsense and is probably not even worth discussing.

It doesn't.

People have used various different frames of reference to describe the system in order to help others to understand. Unfortunately a few people, who refuse to accept the equivalence of inertial frames of reference, misunderstood and siezed on this as some sort of made-up physics.

You can describe the motion of the cart from any frame of reference you like, as has been done time after time in this very thread. Sometimes it's a lot easier to consider alternative frames - for example if you are considering the interaction of the air with a propeller blade it may make it simpler to grasp if you consider the forces involved from the blade's point of view. Alternatively you could look at it from the air's point of view. It gets more complicated to consider it from the ground's point of view since both things are in motion relative to the ground, but I guess if some people absolutely will not accept that any other frame of reference than the ground is "real" then you're stuck with that one.

 

[3point14]

First of all, show me a frame of reference where the air is at rest, outside in the real world.

Find a road pointing in the same direction as the wind is running.

Check the windspeed.

Drive down the road at exactly that windspeed.

Voila - Air at rest, road moving.

Piece of cake.


Of course, that's not the point. The point is that one should be able to look at a thing from any one of a number of inertial frames and the maths still works. All that matters in this instance is that, for something that so many claim is counter-intuitive, it sometimes pays to look at things from a different refernce frame. For this to be of any use to you, you will need to understand what an inertial reference frame is and how it effects what you're measuring.

 

[3point14]

Or perhaps you don't understand why the treadmill has no relation to a cart on a road? Yes I think that is so. Perhaps you should find some qualified physicist who agrees with your misinterpretation of basic physics, and post his name here.

But you see, the cart on the treadmill is an utterly, utterly perfect simulation of a cart on a road.

Really - any qualified physicist will tell you that if you ask the right questions.

If you can't see that the cart on the treadmill is a perfect representation of a cart on the road, then I'm afraid you're just not going to get this.

 

[Llyricist]

First of all, show me a frame of reference where the air is at rest, outside in the real world. Winds don’t move over the ground in response to the motion of the earth’s surface as happens on a treadmill.

Yes they do, the actual movement of the air with the treadmill belt is exactly the same as the slowed air near the ground in the outdoor wind. Ever heard of wind gradient? And if you put obstructions on the belt and created hot and cold areas on its surface, and made it large enough you would create the same sort of weather conditions you talk about next.

What part of "controlled experiment" gives you a problem?

The rest of your argument is nothing but phobia about using an inertial frame of reference other than the ground, couched in terms of "common caveman understanding".

It has been explained over and over that in the frame of reference where the ground is stationary, the moving air provides the energy to feed the feedback loop in the cart itself. Without that moving air the feedback loop grinds to a halt due to losses, with the moving air losing its energy and providing energy to the cart, it keeps going.

However, in the frame of reference where the cart is momentarily stationary, once the cart reaches the wind speed, all the energy does indeed come from the ground and the energy of the air is increased. And the force imbalance will cause the cart to continue accelerating.

Energy is frame dependent...... for the zillionth time.

 

[Jack by the hedge]

You agree the treadmill creates unnatural conditions that do not exist outdoors on the road. Thats a good start to understanding that it is not the same as a road. Good for you!

The treadmill creates controlled conditions. The ability reliably to recreate ideal conditions is obviously convenient. If you are trying to observe a particular effect, it's handy not to have to wait for the weather to deliver the ideal wind. This is not the same as creating a different situation from that which can be found outside. I suspect you understand that.

 

[Jack by the hedge]

Perhaps you should find some qualified physicist who agrees with your misinterpretation of basic physics, and post his name here.

Off the top of my head, Professor Brian Cox.

You can read the first chapter of his and Jeff Foreshaw's book "Why does E=MC²: (and why should we care)" here:

http://www.amazon.co.uk/Why-Does-mc2-Should-Care/dp/0306817586#_

By happy coincidence, it deals with the topic of relative motion and frames of reference in a very digestible way. Happy reading.

 

[Michael C]

First of all, show me a frame of reference where the air is at rest, outside in the real world. Winds don’t move over the ground in response to the motion of the earth’s surface as happens on a treadmill. If you think they do, how would you explain the tornados that just tore through much of the South? Was the surface of the earth spinning wildly around in many different places, causing those wind funnels? You see, you can take these batty reference frame transformations too far, and arrive at all sorts of incorrect conclusions. You may as well stand on your head and call the floor the ceiling, and now your head is touching it. Little kiddies do that sort of thing and we think it’s cute. When grown men do that sort of thing, we call them crackpots.

As I said in response to another poster, you can say a sail cart or a wind turbine is powered by the ground, if it makes you feel somehow superior to say such a thing. But the reality is the planet earth is a large rock with a mass of about 6 x 10^24 kg, more than one million times the mass of the entire atmosphere. Due to gravitational attraction, the atmosphere moves with the planet, with the exception of local disturbances mostly due to temperature differentials and these are what we call winds. The winds are for the most part unpredictable, changing velocity and direction pretty much with a mind of their own, while this big rock we call the earth stays rock solid under our feet, regardless of how it moves through space. Objects sit still on the surface of this big rock due to gravitational attraction and friction with the surface, and it requires energy to move them. It is ridiculous to say that the energy to move them against the friction and gravitational attraction comes from the earth itself, the very thing that is holding things in place! It is ridiculous to say that a road, fixed on the earth’s surface, is going to power something to move along that road, because it most certainly does not do that!

Once again, if you want to act that that little boy, standing on his head and saying his head is now on the ceiling, go right ahead and do so. But you will probably find more than a few people laughing at you.

The kinematic energy for the sail cart is coming from that thing that is filling those sails, the wind and not from the ground. Changing the reference frame does not change reality, only your perception of reality. If your claim for DDWFTTW rests on a change in perception, as it appears it does, then it rests on nothing but nonsense and is probably not even worth discussing.

If you want to continue, then show me some mathematics to support this claim.

Well, that was a very convoluted way of not answering my question. Just so it doesn't get lost, here it is again:

Then you tell me: in the frame of reference in which the air is at rest, where is the kinetic energy of the simple sail cart coming from?

We're not talking about a tornado, we're talking about a normal wind in which it would be possible to run a basic sail cart as already described: a square sail set on a chassis with freely-turning wheels. Let's say the wind is blowing at 5 m/s from west to east. If we use a frame of reference also moving at 5 m/s from west to east to observe the sail cart, where is the kinetic energy of the sail cart coming from?

 

[windgrins]

You seemed to have arrived at a self contradiction.

The energy is coming from whomever or whatever is turning the screw.

Clearly no one is disputing that the energy is coming from outside the system. That is not in question.

But neither face side is different from the other nor does either have different forces. So one must conclude the energy into our gas is entering through both plates-the earth side and the screw side. Otherwise you are saying that even though the plates supply exactly the same amount of force, they don't equally contribute to the energy being supplied to compress the gas. An obvious contradiction. clearly, no acceleration of the object-no unbalanced force. This is very analogous to the cart. There are two points where forces enter the system equally once the cart is at a steady state-the wheels and the propeller. Both components contribute equally as energy paths-just as a keel and a sail on a boat do.

Just like our clamp supplying energy to our cylinder, we can insert the energy of the airmass differential into the cart so it can overcome losses and remain at steady state. This is how sailboats work on most points of sail and all where they have a VMG greater than WS. This works just as well for a sailboat sailing on a 10Knt current with no surface wind as a sailboat on still water with a surface wind of 10Knts. The boat doesn't recognize any difference and sails at the exact same speed with relation to the water or air.

If you believe otherwise, check the book written by a physicist-The symmetry of Sailing by Ross Garrett. The author is a very accomplished physicist who retired from the staff of the Physics dept of Univ of Auckland.



WindGrins

 

[jadebox]

profpangloss, I will be happy to run you through a series of yes/no questions that will show you that the cart on the treadmill is equivalent to the cart on the road at wind speed. I will tell you ahead of time that all of the answers are yes and only require explanation if you claim an answer is no.

Bummer. I was interested in seeing how this would play out, but I guess the impossibility of humberizing "yes/no" responses discouraged profpangloss from participating.

-- Roger

 

[jduffy77]

You agree the treadmill creates unnatural conditions that do not exist outdoors on the road. Thats a good start to understanding that it is not the same as a road. Good for you!

It sounds like you are having trouble with the meanings of some of the words here.

Equivalent does not mean "the same as". The difference may be hard to understand at first so there is no shame in spending a little time with Google, especially if English is not your first language.

ETA: It is also true that the difference may be harder to understand if you have no experience in math or physics (also no shame in that).

 

[humber]

I think you missed the point entirely. Sol's point was not that a belt is the same as the wind. Perhaps it would help if it were laid out differently:


Any clearer now?

Still 100% wrong.

 

[humber]

You really don't understand this at all, do you.

That's okay, lots of people cleverer than you didn't get it the first time, don't be so down on yourself. Keep studying, keep thinking about it and one day it will just go 'ping' (like a lightbulb).

Start with learning a little about inertial frames and go from there. Do make sure you understand each section before you move on to the next, I think that's perhaps been your problem until now.

Keep on with the study and, above all, keep an open mind, you'll get it in the end!

As if. The proselyted ideas are a simple-minded confection of physics.
The trial data says you have fool's gold.