Merged DDWFTTW in a “Real” Wind

[profpangloss]

Frames of reference have no intrinsic boundaries.

You are imposing a boundary by trying to look at only the top of the belt. An "X" marked on the top of the belt would move out of such a limited frame. I am trying to show you how absurd such a frame of reference is. If you insist on using a frame based on a projection of the motion of the upper belt, you have two choices:
1) The frame has no boundaries, and the "X" on the belt is seen to be rotating in that frame and the power from the rotating belt is frame invariant, unlike the wind.

2) The frame would need to be bounded on the upper belt and then the "X" is then seen to leave the frame, making such a frame ridiculous.

Take your pick.

 

[humber]

Humber, you are too far off the rails at this point to bother, and it's 2:30 am here.

All that crap about ice boats is of your own making, I didn't bring them up, you did. I made this claim:

And you said this:

And you refused to back it up. Instead you started throwing red herrings left and right, including goading me to do yet another power analysis of the cart, of which I do several hundred in a matter of seconds.

There are countless references that show an iceboat can achieve 2WS in a 15mph wind. No sweat. If you are too lazy to find them, then don't ask about boats.

But, there is nothing to explain. The cart does nothing of interest. A soap box derby.

Like the small cart in the street, which struggles to start, fails, slides and then reaches 5mph when a leaf reaches 20mph, that is then promoted as something to be explained. Is that the game? Defy your own evidence and see if you can get away with it?

There is nothing about the BB that needs to be explained. It managed only 28mph in winds of at least 15mph, and when 20 degrees off ddw. Not only that, but there are both lateral and vertical gradients.
So what?

It won't change by converting force to power and back, or using torque * AV, or any other gimmicks you try to throw. It's old hat, everyone understands it. It always boils down to the simple equation I posted.

And where is there mention of torque or AV? Oh, they are your red herrings.
Your equation is wrong, whereas, this is correct. The cart fails even the simplest of power analysis.

There is not enough power to defeat the losses, and they are unrealistically low. This stands, and will not fall.

The power required to overcome the aerodynamic drag is given by:

[latex]P_d = \mathbf{F}_d \cdot \mathbf{v} = \tfrac12 \rho v^3 A C_d<br />[/latex]

v^3 is When v = ground speed = windspeed, but the cart moves wrt respect to both the wind and the ground, so V cannot be the same for both frames.

F_Drag = K*Vhead^2 ( Vhead = Vwind -Vcart)
The retarding force generated by the wind on the cart, wrt the wind.

The cart must oppose that force, but is traveling at Vcart so
Power = F_drag*Vcart
Power = K*Vhead^2*Vcart
The power required to overcome the aerodynamic drag relative to the ground.

 

[semper]

Good. You agree that in an IFOR based on a projection of the upper belt's motion, the belt will be seen to be changing direction. In fact, it will be seen to be rotating and the power available from that belt is frame invariant. This is not the same as the power from the wind.

So, is this another aspect of the Profpangloss Limit?

Um, how is it that a reference frame having the ground fixed (fixed to the ground) can ever be considered Inertial? Have you ever really studied this stuff beyond high school?

 

[semper]

I mean, its fine to study it here, but you have to be able to listen, and beware of those peddling inconsistent, self-contradictory theory which cannot be shown in practice to work and which is not supported by easily referenced widely accepted literature.

 

[profpangloss]

So, is this another aspect of the Profpangloss Limit?

You should not be so modest! The limit you imposed on propeller thrust is entirely of your own making, as I imposed no such limit. So by all means, please take a bow and take full credit for it, and from here on out refer to it as “Semper’s Limit”.

Um, how is it that a reference frame having the ground fixed (fixed to the ground) can ever be considered Inertial?

According to this source: http://www.real-world-physics-problems.com/inertial-reference-frame.html

When applying the equations of motion for problems on earth, it is common practice to “attach” a coordinate system to the ground and assume that this is an inertial reference frame. However, it is not quite, since the earth itself rotates and the earth in turn revolves around the sun, etc. However, the rotation rate of a (ground) reference frame attached to the earth is very small, and its acceleration is also very small, so for practical purposes it can be treated as an inertial reference frame.
To show this, let’s determine the rotation rate and acceleration of a ground reference frame attached to the earth (so that it moves with the earth).
The rotation rate of the earth is one full revolution (2π rad) every 24 hours. The angular velocity (rotation rate) of the earth is therefore w = 7.3x10-5 rad/s. This is equal to the rotation rate of the ground reference frame. As you can see, it is very small.
Therefore, a ground reference frame attached to earth can be treated (with a high degree of accuracy) as an inertial reference frame.

"Therefore, a ground reference frame attached to earth can be treated (with a high degree of accuracy) as an inertial reference frame."


Compare that angular velocity to a belt that is running at 5 m/s, and it goes around the cylinders at both ends, the angular velocity can be quite high. In approximate numbers, with a cylinder of 0.4m circumference, the angular velocity is close to 80 rad/s. So the belt will be subjected to inertial forces at both ends where it goes around the cylinders and those forces cannot be isolated from the rest of the belt!

Have you ever really studied this stuff beyond high school?

More insults? Is that really all you carteers have to offer?

 

[semper]

You should not be so modest! The limit you imposed on propeller thrust is entirely of your own making, as I imposed no such limit. So by all means, please take a bow and take full credit for it, and from here on out refer to it as “Semper’s Limit”.





According to this source: http://www.real-world-physics-problems.com/inertial-reference-frame.html



"Therefore, a ground reference frame attached to earth can be treated (with a high degree of accuracy) as an inertial reference frame."


Compare that angular velocity to a belt that is running at 5 m/s, and it goes around the cylinders at both ends, the angular velocity can be quite high. In approximate numbers, with a cylinder of 0.4m circumference, the angular velocity is close to 80 rad/s. So the belt will be subjected to inertial forces at both ends where it goes around the cylinders and those forces cannot be isolated from the rest of the belt!



More insults? Is that really all you carteers have to offer?

Do you find that question insulting?

Quoting literature is fine, but not really sufficient to be your argument.

I will look in my atlas for where the reference frames are, perhaps they are not permanently attached, how often do they move them around? Would they not become tourist attractions?

What would you say is the angular velocity of the flat part of the belt?

 

[humber]

I will look in my atlas for where the reference frames are, perhaps they are not permanently attached, how often do they move them around? Would they not become tourist attractions?

The Humber is considered to be both attractive and a reference, Semper.

It looks like the TM may be the Galilean Equivalent of a cart on a belt, Semper.

 

[semper]

The Humber is considered to be both attractive and a reference, Semper.

I recently asked a boat driver who had plenty of experience crossing fast flowing rivers how much rudder he had to hold in order to go across in a straight line. He confirmed that the vector methods work just fine, and since the aerodynamic loads are insignificant, the hydrodynamics are just fine with nil rudder input once on course. I'm not sure if he has Navigated the Humber.

ETA, oh, I see you snipped your comment on the boat and river vector problem you had referred to before my reply came up, interesting habit of yours isn't it?

 

[humber]

I recently asked a boat driver who had plenty of experience crossing fast flowing rivers how much rudder he had to hold in order to go across in a straight line. He confirmed that the vector methods work just fine, and since the aerodynamic loads are insignificant, the hydrodynamics are just fine with nil rudder input once on course. I'm not sure if he has Navigated the Humber.

ETA, oh, I see you snipped your comment on the boat and river vector problem you had referred to before my reply came up, interesting habit of yours isn't it?

I decided is was superfluous, Semper, but now that you have mentioned it, perhaps the reason the rudder works, has something to do with fluid dynamics.
One can draw a vector across a room, but the mechanics of that same salty sailor walking across that room, are a lot more complicated than that.


Ahem...Progpangloss has posted a reference to back up what he is saying, but as always, Carteers think that is a bad thing; as if learning and information somehow tainted the purity of insight.
Such references are often referred to as "cutting and pasting" and "quoting literature", though published papers without references or bibliography are not only unusual, but rather frowned upon, yet you offer an anecdote.

 

[semper]

I decided is was superfluous, Semper, but now that you have mentioned it, perhaps the reason the rudder works, has something to do with fluid dynamics.
One can draw a vector across a room, but the mechanics of that same salty sailor walking across that room, are a lot more complicated than that.

Almost all your posts are superfluous Humber, you should consider deleting far more often.

It has been shown before, but on a room sized treadmill, ordinary walking can get you straight across the room using vector methods to set course.

 

[profpangloss]

Quoting literature is fine, but not really sufficient to be your argument.

It isn't "literature" Semper. It is Physics.

I will look in my atlas for where the reference frames are, perhaps they are not permanently attached, how often do they move them around? Would they not become tourist attractions?

So your argument is reduced to the semantics of “fixed” versus “attached”? How trite! How desperate!

“how is it that a reference frame having the ground fixed (fixed to the ground)”

What would you say is the angular velocity of the flat part of the belt?

How do you propose to isolate the flat part of the belt from the inertial forces acting on the belt as it goes around the cylinders? Does the belt have some sort of Semper Inertial Force Isolator built into it? Similar to Semper's Limit on propeller thrust?

 

[humber]

Almost all your posts are superfluous Humber, you should consider deleting far more often.

It has been shown before, but on a room sized treadmill, ordinary walking can get you straight across the room using vector methods to set course.

I doubt that. Try standing one one leg when on a treadmill.

 

[semper]

It isn't "literature" Semper. It is Physics.

Really?

So your argument is reduced to the semantics of “fixed” versus “attached”? How trite! How desperate!

Not really, but it is vital to be careful with definitions in this business.

How do you propose to isolate the flat part of the belt from the inertial forces acting on the belt as it goes around the cylinders? Does the belt have some sort of Semper Inertial Force Isolator built into it? Similar to Semper's Limit on propeller thrust?

I cannot take the credit, as I don't think propeller thrust is solely a function of input power.

Nor can I take credit for the proposed SIFI. The mechanical effects on any element of belt in the flat section accord with all normal principles. When the belt is running at constant rate, the belt particles on flat sections are not being accelerated.

Do you agree with Humber that walking on a constant rate belt will need some sort of special technique?

 

[semper]

I doubt that. Try standing one one leg when on a treadmill.

Yeah, I did that recently at the airport, no trouble at all. I could imaging some people would find the visual cues disrupt their balance, but I was ok, lucky I guess.

 

[humber]

Yeah, I did that recently at the airport, no trouble at all. I could imaging some people would find the visual cues disrupt their balance, but I was ok, lucky I guess.

Well, Semper, I don't use airport belts because they are too slow, so I suppose you are lucky in that they accommodate you.
If at running speed, the belt would quickly pull your foot from under your COG, and you would find that it is much harder to maintain balance, if you didn't fall over.

I see that you have asked another question, unrelated to what I said, but you will find a great number of references outlining the many difference that the belt makes. When running, the torso moves over the foot that has been planted ahead, while the other swings as a pendulum on return. That is one of nature's energy-saving schemes, Semper. But, on a belt, the torso does not move over the foot placed ahead, but is pulled back by the belt.

 

[semper]

Well, Semper, I don't use airport belts because they are too slow, so I suppose you are lucky in that they accommodate you.
If at running speed, the belt would quickly pull your foot from under your COG, and you would find that it is much harder to maintain balance, if you didn't fall over.

If you are in a hurry Humber, it is possible to walk while on the belt. They don't usually put up signs to tell you this, but walking while on the belt will get you to the end in less time.*

*The airport authorities make the assumption that you will know to walk in the same direction the belt is going with respect to the terminal. There may be age and disability restrictions as well.

 

[semper]

I see that you have asked another question, unrelated to what I said, but you will find a great number of references outlining the many difference that the belt makes. When running, the torso moves over the foot that has been planted ahead, while the other swings as a pendulum on return. That is one of nature's energy-saving schemes, Semper. But, on a belt, the torso does not move over the foot placed ahead, but is pulled back by the belt.

And yet astonishingly, walking on the airport belt feels exactly the same as walking anywhere else, and, there is not even special training required or provided.

Take note of the first scene here;
http://www.youtube.com/watch?v=ZPyDY5aZyXs

oh and most of the rest apply in some way.

 

[humber]

If you are in a hurry Humber, it is possible to walk while on the belt. They don't usually put up signs to tell you this, but walking while on the belt will get you to the end in less time.*

*The airport authorities make the assumption that you will know to walk in the same direction the belt is going with respect to the terminal. There may be age and disability restrictions as well.

When walking one particular belt at Melbourne's Tullamarine airport, while staring ahead, but letting your eyes relax, one can get the sensation of moving rapidly backwards or forwards. The airport does not advertise that fact, because it encourages unruly behavior.

But, the general difficulty with walking on airport belts, are those ahead standing with luggage, Semper. But, when not so occupied, they are truly a wonder.

And yet astonishingly, walking on the airport belt feels exactly the same as walking anywhere else, and, there is not even special training required or provided.

It seems that a lot of well-meaning researchers have wasted a great deal of time studying the matter when they could not only have been enjoying the magic, but also that afforded by unfettered ignorance, Semper.
Differences include running gait and energy consumption. All measured.

 

[semper]

It seems that a lot of well-meaning researchers have wasted a great deal of time studying the matter when they could not only have been enjoying the magic, but also that afforded by unfettered ignorance, Semper.
Differences include running gait and energy consumption. All measured.

Gosh, if you say so Humber. I would have thought these studies would have made the headlines though, overturning centuries of successful theory after all. Oh well, life aboard ships, aircraft, trains etc etc will never be the same huh? All those who only had the illusion of equivalence, how will they cope?

 

[jduffy77]

Well, Semper, I don't use airport belts because they are too slow, so I suppose you are lucky in that they accommodate you.
If at running speed, the belt would quickly pull your foot from under your COG, and you would find that it is much harder to maintain balance, if you didn't fall over.

Humber I just realized that much of your views of the cart are driven by our fundamental misunderstanding of what you know about the universe. Perhaps we should spend some time establishing the truth about the Earth on a more basic level.

I know that the Earth is immovable and firm, but I am not clear on some details of the firmament. How high are the columns of mountains which hold up the sky? Are the stars attached to a sixth sphere or are they a fixed part of the firmament?