The reality of energy.
in [Relativity]
|
From: ben6993 on 27 Feb 2010 14:22 On Feb 27, 3:34 pm, PD <thedraperfam...(a)gmail.com> wrote: > On Feb 26, 7:54 pm, glird <gl...(a)aol.com> wrote: > > > On Feb 23, 4:48 pm, Occidental wrote: > > > >< Discussion in physics refer to energy as if it were as fundamental a part of the universe as space, time and matter. In Newtonian mechanics, energy is a useful mathematical abstraction, but not a directly measurable part of any dynamical system. Presumably this is also true in Relativity, despite mass/energy equivalence. > > > Before replying to this message I glanced through the previous nine > > replies. As I expected, none of them defined "energy". Having long > > ago noticed that unless a key word is defined nobody understands what > > other people mean when they use it, I defined it thus: > > "Energy" is the ability to do work, > > The above is a common definition, yes. > > > an ability that is possessed by > > organized portions of matter. > > Not just by matter. > > > > > > > glird- Hide quoted text - > > - Show quoted text -
From: PD on 27 Feb 2010 15:04 On Feb 27, 1:22 pm, ben6993 <ben6...(a)hotmail.com> wrote: > > "Energy" is the ability to do work, an ability that is possessed by > > organized portions of matter. > > I have noticed a definition in wiki which seems to imply that energy > is more complicated than the definition above: > "The thermodynamic entropy S, often simply called the entropy in the > context of thermodynamics, can provide a measure of the amount of > energy in a physical system that cannot be used to do work." (http:// > en.wikipedia.org/wiki/Introduction_to_entropy) > > If energy is the ability to do work, but at the same time entropy > implies that some portion of energy is not available to do work, then > how do we re-define that portion of the energy in a system not > available to do work? Is there a more complex definition of energy? That's actually an excellent point. Kinetic energy, one of the forms of energy, is divided into stochastic and collective energy. The collective energy is the kind of thing you would write (1/2)mv^2 for a baseball of mass m. Stochastic energy is that which is indicated (but not measured) by a thermometer; it is the *random* kinetic energy of the individual molecules in the body. The former can be wholly converted into work. The latter can only be partially converted, with the limit set by Carnot's Theorem. In addition, rest energy (the energy associated with rest mass) can't be converted into work, but the entropic definition above has nothing to do with this. I don't know of any other cases, off the top of my head.
From: BURT on 27 Feb 2010 15:12 On Feb 27, 12:04 pm, PD <thedraperfam...(a)gmail.com> wrote: > On Feb 27, 1:22 pm, ben6993 <ben6...(a)hotmail.com> wrote: > > > > "Energy" is the ability to do work, an ability that is possessed by > > > organized portions of matter. > > > I have noticed a definition in wiki which seems to imply that energy > > is more complicated than the definition above: > > "The thermodynamic entropy S, often simply called the entropy in the > > context of thermodynamics, can provide a measure of the amount of > > energy in a physical system that cannot be used to do work." (http:// > > en.wikipedia.org/wiki/Introduction_to_entropy) > > > If energy is the ability to do work, but at the same time entropy > > implies that some portion of energy is not available to do work, then > > how do we re-define that portion of the energy in a system not > > available to do work? Is there a more complex definition of energy? > > That's actually an excellent point. Kinetic energy, one of the forms > of energy, is divided into stochastic and collective energy. The > collective energy is the kind of thing you would write (1/2)mv^2 for a > baseball of mass m. Stochastic energy is that which is indicated (but > not measured) by a thermometer; it is the *random* kinetic energy of > the individual molecules in the body. The former can be wholly > converted into work. The latter can only be partially converted, with > the limit set by Carnot's Theorem. > > In addition, rest energy (the energy associated with rest mass) can't > be converted into work, but the entropic definition above has nothing > to do with this. > > I don't know of any other cases, off the top of my head. Kinetic energy is mass. Mitch Raemsch
From: Y.Porat on 27 Feb 2010 15:21 On Feb 27, 3:54 am, glird <gl...(a)aol.com> wrote: > On Feb 23, 4:48 pm, Occidental wrote: > > > > >< Discussion in physics refer to energy as if it were as fundamental a part of the universe as space, time and matter. In Newtonian mechanics, energy is a useful mathematical abstraction, but not a directly measurable part of any dynamical system. Presumably this is also true in Relativity, despite mass/energy equivalence. > > Before replying to this message I glanced through the previous nine > replies. As I expected, none of them defined "energy". Having long > ago noticed that unless a key word is defined nobody understands what > other people mean when they use it, I defined it thus: > "Energy" is the ability to do work, an ability that is possessed by > organized portions of matter. > > glird --------------------- just mass in motion!! no need for big philosophy ! E = mc^2 that s all the story !! what is unbelievable is that so few people understand it: it started with that block of understanding that energy has mass started with the idiotic notion that no mass can reach c but all those dumbo s (mathematicians )that consider themselves physicists - could not think about the possibility that there is an exception to that 'rule' ie the photon CAN move at c !!! actually you could see it based on the **trend** of experimental data ie as mass is smaller and smaller it can reach closer and closer to c !!! what can be simpler than that ??!! not to mention that hf ie h contains mass !!! not relativistic and not shmelativistc mass just the one kind that exits !!! no need to invent each Sunday and Monday i new kind of mass !!! ATB Y.Porat ------------
From: Androcles on 27 Feb 2010 15:33
"ben6993" <ben6993(a)hotmail.com> wrote in message news:8568dbb7-ba06-4b3e-a352-25a90f8560c7(a)q15g2000yqj.googlegroups.com... > "Energy" is the ability to do work, an ability that is possessed by > organized portions of matter. I have noticed a definition in wiki which seems to imply that energy is more complicated than the definition above: "The thermodynamic entropy S, often simply called the entropy in the context of thermodynamics, can provide a measure of the amount of energy in a physical system that cannot be used to do work." (http:// en.wikipedia.org/wiki/Introduction_to_entropy) If energy is the ability to do work, but at the same time entropy implies that some portion of energy is not available to do work, then how do we re-define that portion of the energy in a system not available to do work? Is there a more complex definition of energy? ================================================ You haven't defined work. Lifting x gallons of water a height of y feet from a mine is "useful work" for an engine, but if that engine burns coal to raise steam to do the work and then the heat is simply lost to atmosphere, that portion of energy the coal had which didn't do useful work is still called energy. Entropy says you can't make 100% of the coal's energy lift water, some will always be lost as heat. This leads to silly arguments about "closed systems" which don't exist, fools devising perpetual motion machines, and misunderstood definitions of entropy. Entropy is a theoretical physicist's lame attempt to face practical reality and place his own stamp on it. |