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Re: cadence [gciriani]
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Re: cadence [Tom A.]
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Re: cadence [Frank Day]
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The question here is: Stupidity or dementia?
Maybe we could have a poll!
Maybe we could have a poll!
Re: cadence [tigermilk]
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Exactly which one of these definitions of "machine" does the simple pendulum satisfy? I simply don't see the simple pendulum as a machine. I guess you could claim that a spinning disk is a machine also. A spinning disk is something that should continue forever unless acted upon by an outside force. Both the simple pendulum and the spinning disk is in equilibrium with itself. The MMF system converts an up and down motion to a rotational motion satisfying both definitions 1a and 1b. If loaded, as when riding a bicycle, it also satisfies definition 2.
Yes, it should be possible to work this entire problem out mathematically. The only issue would be the assumptions used for calculating the losses in the materials used. What would one use for the soft tissue of the leg for instance?) If there is an adequate system for analyzing this why doesn't some one do it and prove me wrong. All we have is hyperbole coming from the believers in the preposterous notion that this machine has no losses.
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Frank,
An original Ironman and the Inventor of PowerCranks
Re: cadence [bjohn34]
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Re: cadence [Frank Day]
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Regarding the "MMF", you do realize that if someone were to model this, the FIRST step would be to assume a rigid body system don't you? That's engineering 101 at work there. Same thing with a mass-spring system. You start with the "unrealistic" model of no losses which actually tells you a WHOLE lot. You can bump up the fidelity and add damping and such as you get smarter or more adventurous, neither of which I'd suggest in your case for obvious reasons :) But as you add those "losses" you better have some good data. For this particular problem you could merely parametrically investigate the effects of various system damping, friction losses, and such.
Any "machine" is a construct of your own devise. As demonstrated above, you can set the analytical problem up to have no losses. If you throw this mechanism in a multibody dynamics program and specify no losses, then you will get a perpetual motion machine. You absolutely have to as you've specified no losses due to damping, friction, heat, hysteresis, etc. If you're simulation comes back otherwise, the program isn't implementing the equations of motion properly.
Your obvious mistake is trying to interject what you see in nature (the lack of perpetual motion machines) and pigeonhole it into idealized models that we engineers utilize every day in design and analysis. You see that as a flaw in the methodology. We see that as an idealization that gets us 99% of the info we want.
Re: cadence [tigermilk]
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I understand that. A rigid model is useful for looking at forces and stresses on materials but not much else. As I said above, how is such a model useful for modeling real world energy losses if that is what you are interested in studying?
No, my "mistake", at least from your view, is not falling into line and accepting the prevaling view that an idealized model that ignores the possibility of internal losses is a good model to analyze internal losses in real life. I don't buy it. I am surprised that you are taking this side. What is your evidence that this is a good model for this purpose?
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Frank,
An original Ironman and the Inventor of PowerCranks
Re: cadence [Frank Day]
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Quote:
Frank Day: How could it be? Why can't anyone but me here see that? The rigid body model assumes internal losses are negligible. But, experimentally we know that when pedaling internal losses are not trivial, at least when the model is unloaded, according to Papadapalous.
Giovanni Ciriani
http://www.GlobusSHT.com
Re: cadence [Frank Day]
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I never said any such thing.
There is nothing to admit, since your claim above is patently false.
As I have said before, see Jim Martin's work (among others).
Re: cadence [Tom A.]
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Re: cadence [gciriani]
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Frank,
An original Ironman and the Inventor of PowerCranks
Re: cadence [Frank Day]
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We don't...it's just that when modeling one starts with the simplified, idealized model FIRST so that you can get a measure of the forces acting on the various links, pivots, and boundary conditions. THEN you begin to start incorporating the less idealized, more realistic effects so that there is a better understanding of their magnitudes, etc.
YOU however, can't even get the your brain wrapped around the SIMPLEST model and keep insisting that even if all friction was assumed to be zero and the links are infinitely rigid, then there would STILL be some sort of energy losses just from the basic physics of the device. That is demonstrably NOT so since it would violate both the 1st law of thermodynamics and Newton's first law of motion. As Andy pointed out, the 2nd law of thermodynamics is NOT being violated since a priori it is assumed for the modeling purposes that entropy is just not DECREASING.
THAT'S where the disconnect is Frank...inside YOUR head. You say that the idealized model once set in motion would slowly come to a stop. That is NOT so until we start adding losses into the system model. But, there's no way of knowing the magnitudes of those losses until you do the force analysis of the simplified, idealized model FIRST.
We're just trying to get you to the first step...and you can't even get THERE...
I fully expect you to come back with some sort of response claiming how there HAS to be losses even in the idealized "lossless" model, so go right ahead and just keep mixing up idealized vs. non-idealized cases in your head and complaining about how everyone in the universe gets this wrong and you're the ONLY one who is getting this right.
http://bikeblather.blogspot.com/
Re: cadence [Tom A.]
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Frank,
An original Ironman and the Inventor of PowerCranks
Re: cadence [Frank Day]
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No, the implication (fact/conclusion, actually) is that such losses are non-existent as you envision them.
Re: cadence [Andrew Coggan]
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Frank,
An original Ironman and the Inventor of PowerCranks
Re: cadence [Andrew Coggan]
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Re: cadence [Frank Day]
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See...you're still not getting it. The idealization DOES NOT violate the second law, it merely assumes that the entropy does not DECREASE in the system, i.e. it is in equilibrium. Energy neither flows into or out of the system. The 2nd law of thermodynamics DOES NOT state that the idealized machine is impossible.
I'm not going to go through the whole thread again to find all the cases, but I know I have said so, amongst others. The issue all along has been that you have INSISTED that there is an energy loss irrespective of the internal losses in the materials, at the joints, etc....such that even assuming that all of those losses didn't occur, there STILL would be some other loss just by virtue of the configuration of the machine. That is just not so.
No...the implication ALL ALONG is that there aren't any losses separate from those internal losses, of which you have been adamant in saying that there is...
http://bikeblather.blogspot.com/
Re: cadence [Tom A.]
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If you or anyone else has said that I surely must have missed it. But, regarding what I have said I must say phooeey. What I have said is there must be an energy loss and the only way I can explain it is through an energy loss in the materials. The second law requires an energy loss if energy is transferred between elements not in equilibrium. If you want to argue that not allowing energy loss by using materials that only exist in the imagination somehow allows one to get around this law then so be it, it is like arguing how many angels can exist on the head of a pin. The issue all along in this thread goes back to my comment that the movement of the thigh in the pedaling motion causes an energy loss and you during a brain fart agreed with me. When Dr. Coggan asked you if you missed that you quickly corrected yourself. The perfect MMF only came up as evidence to support your side of the argument that there is no energy cost to the motion. Of course, that example has no similarity to reality but little fact seems to not bother you or Dr. Coggan or anyone else. You would prefer to argue this little BS issue rather than discuss the original issue (probably because you know you can't win).
Huh? Just exactly what does that mean? I don't have a clue what you mean by that statement. Perhaps it would help me if you could list all of the losses that need be accounted for between the muscles and the wheel to add up to the whole. Seems to me I asked that question many pages ago and never got an answer.
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Frank,
An original Ironman and the Inventor of PowerCranks
Re: cadence [Frank Day]
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Frank, just give it up.
BTW, you do know that there's absolutely no reason to invoke thermodynamics in kinematics don't you? Lots of spacecraft, aircraft, automobiles, etc have been designed without that.
Just because you can't comprehend it doesn't make it wrong. Show some humility. I show my humility by deferring to those mathematicians, engineers, and physicists who came before my time. I suggest you do the same.
If you REALLY think you are right, read up on dynamics (get a book, not wikipedia) and get back to us.
BTW, you do know that there's absolutely no reason to invoke thermodynamics in kinematics don't you? Lots of spacecraft, aircraft, automobiles, etc have been designed without that.
Just because you can't comprehend it doesn't make it wrong. Show some humility. I show my humility by deferring to those mathematicians, engineers, and physicists who came before my time. I suggest you do the same.
If you REALLY think you are right, read up on dynamics (get a book, not wikipedia) and get back to us.
Re: cadence [tigermilk]
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Anyhow, I spent the first few pages of this thread trying to make my point without invoking thermodynamics. Once I discovered the thermodynamics argument makes my point so well I have decided it is easier to stay with it. If someone wants to come here and argue that there is no energy loss inherent in the pedaling motion all I need to is throw out the 2nd law in rebuttal. While it may seem possible to many the 2nd law simply says it is not possible. No need to get into the details as to exactly where the analysis fails, it simply does.
I would prefer this thread to have evolved to our now "discussing" how large the losses are under different circumstances (different masses, different cadences, different bike and crank construction materials) but it is not possible as long as people prefer to deny that these losses can exist or continually focus on whether it is possible to built a bike out of materials that cannot exist in order to avoid this loss. It is a smoke screen to avoid admitting one has made an error.
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Frank,
An original Ironman and the Inventor of PowerCranks
Re: cadence [Frank Day]
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There is no energy loss inherent in the pedaling motion.
Re: cadence [Frank Day]
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Re: cadence [Andrew Coggan]
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Frank,
An original Ironman and the Inventor of PowerCranks
Re: cadence [Frank Day]
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The entropy of the system doesn't change, dumbass...
If the Naval Academy couldn't teach him elementary physics...what makes you think that you (or I...or anyone else) can? ;-)