The physical work is kind of energy transformation

An attempt has been made by me some years back to address this problem. See my article: "The concept of Biophysical work".

The definition of "work" is useful because of the work-energy theorem. A definition of a term is useful when a rigorous theorem can be proven relating it to other well-defined terms

I'm not sure I fully agree with your reasoning. A man pushing a wall is performing work in a strict sense. Myofibrils in muscles are contracting against force related with pushing the wall. There is a compression/stretch of the tissues (e.g. muscles, tendons), slight deformation of the bones. All against force of the wall. And contraction of the muscle is not really constant - actin and myosin filaments relax every so often causing local deformation of molecular structure of myofibrils which is then restored by consecutive contraction cycle. So I think on microscale there is a lot of deformation against the force (which is work). But there is also chemical energy involved with ATP->ADP cycle, heat generation and lots of other reactions. So I wouldn't say that there is total lack of physical work.

If the system is taken as the entire man, including all the molecules that make up this person, then the system is doing no work on the external world and no work is being done to the man. The man may not be thermally isolated from the wall and heat energy may be transferred from the man to the wall.. Heat transfer will be negligible if the man's hand is encased in styrofoam.

If the system consists of some subset of molecules, e.g.., a muscle, then the muscle is not isolated from the rest of the molecules that make up the complete man. As you say, the muscle is neither mechanically nor thermally isolated and work and heat will be non-zero in the process In addition, as you remarked, the chemical energy changes too.. The internal energy of the muscle changes, i.e., the average kinetic energy of the muscle's molecules is altered during the process..

It's unnecessary to alter the usual definition of "work," and the work-energy theorem applies to any chosen system of molecules.

The physical work is kind of energy transformation

Maybe the problem is that we are thinking only the concept of work in terms of forces (F) and distances (ds) following the definion as Wab=∫F ⃗∙ds ⃗ . However, the change of work can be also defined as a change in energy, according to the expression ∆Wab=(E_K (b)+E_p (b))-(E_K (a)+E_p (a)), where E_K and E_P are the kinetic and potential energies respectively. Obviously we can measure the energy consumed to push the wall or walking with a mass on the head. In a physical sense (strictly speaking) the two men are doing a work that can be precisely defined.

I can’t see any inconsistency or problem in the definition of work in terms of energy differences.

Hi everyone,

many many thanks for the suggestions and answers from one and all.

The point is " The poor coolie/porter should get his due" -- even in terms of physics and physical laws, not because of labor laws! Kuklik is right and indeed physiological work is done. So a modification is called for. Physics can enter and modify all other fields and we should not have objections to the vice versa, provided there is sufficient reason.

As suggested by Pastor, we should modify the fundamental definition of work as any exchange (income/expenditure) of energy in any manner whatsoever, as follows from the work-energy theorem, and of course, we should not then use "capacity to do work" as the primary definition of energy. The F.ds definition is useful for specific preliminary cases only, where the force and the displacement are explicitly known. The proposed redefinition of work primarily as "energy exchange" for more complex systems automatically includes F.ds also.

Rosensteel's thoughts are precisely the ones that should engage us. We must not forget that man is not a rigid body. It has fluidity and hence the internal forces can do work on the system as well as on the surrounding. So what/ who constitutes the man really? The collection of molecules making up the physical body, or something else? Is it in the realm of Physics, physiology, psychology or philosophy? Truly interdisciplinary question indeed! How are we able to willfully direct the internal forces which are electromagnetic in character? Is the hypothesis of Vital force as an agency untenable?

Thanks everyone again.

I'm sorry, but in my opinion this is entirely a false problem. You must ttake into account that in Physics most words used to define concepts has not the same meaning as in everydaylife (even if concepts are normally related).

So the effort is not to change the definition of work but to make clear that words in physics have always a very technical meaning.

Loosing this technical meaning implies loosing the precision of the concept and the impossibility to make a valid description of reality.

@ Henk Smid,

No, I didn't teach thermodynamics, but I had lot of focus during my studies on statistical physics (so of course thermodynamics as well). But I think a biology is the main contributor here (in this example of man pushing wall). We should know a bit about physiology of muscle work before attempting to describe work in physical understanding.

I am sorry, maybe I missed something. I don't see any problem here. In my opinion, the definition of physical work is adequate and has been tested for generations.

Of course what you regard as work depends on how you draw the boundary of your system. The man pushing on the wall clearly does no work on the wall and none on the floor. What's been called physiological work manifests as increased heat dissipation and so is not work. A man walking with no load in addition to his body does work raising his body by small amounts at each step which is presumably dissipated in a foot fall as his body is lowered for the next step. So a man with a load expends more dissipated energy than one with no load. The cycle is small work followed by small dissipation which adds up to zero work and net dissipation.

In the case of an orbiting body, it's not true that kinetic energy doesn't change. The orbit is elliptical in general so there is periodic trade off between kinetic and potential energy and so it's the sum that remains constant and we say that it's a conservative system. In a similar situation, take a car going up one side of a hill and down the other. Clearly the car does work going up which if it's not a Prius is dissipated going down the other side, assuming the car can't just keep accelerating going down.

Dear James and others,

The point is whether additional energy dissipated as heat is to be considered as work by the man or not?

Even if you stick to the definition that work is increase of KE of a system on which the work is done, then in this case work is done on the surroundings since the dissipated energy goes to increase the total KE of the environment..

Next point, you think that the porter in the return stroke after the slight lifting allows the box to fall freely. It is not so since he may get a stiff neck then! What he does is to apply some force in the opposite(upward) direction so that it falls with constant velocity with gravity balanced by the pull. This pull is due to the muscular forces which support the box during the fall. But suppose your point is taken that there is free fall in the return stroke. Even then the man does not gain any energy by the pressing of the box on his head, which gets temporarily deformed and then elastically regains its shape, again spending more biological energy (include the excess heat generated during the restoration) than was supplied by the pressure of the box during the deformation.

Finally, when energy in any form is lost by the system (porter here), why should we stop short of calling it work by the system? The energy thus released will certainly add to the KE or PE of the surrounding.

So the additional energy lost on account of pushing the wall or during walking should be considered as work.

I admit that It is very difficult for us to get rid of ideas so deeply ingrained in us from our school days, but sometimes it may be a necessity. Nothing in science is sacrosanct. If it is so, then it becomes like a dogma in religions.

Dear Charles,

Please don't misunderstand my last remark which applies equally well to me as well.

Have we not witnessed such things in the history of science? Actually, no offense was meant to anyone by that. I just wanted to point out that it is really difficult to think otherwise than we are taught to. It applies to you me and everyone of our human family in any field of endeavor, not just science. It just requires a little detached thinking which everyone is capable of. So no question of abusing anyone, which would be quite unbecoming of us who are endeavoring to know the truth of things through science, and no sacrifice is too great for the sake of that truth, which would open the boundary of science a little bit so as to accommodate a fact from some other field within its ambit by a simple redefinition of a term like work. I hope, this will put things in place, in case you or anyone else still have any misgivings. In fact it pains me to find that you have been hurt by that remark, which I wrote with full consciousness of the fact that I also need straightening out my understanding in several areas from many people like you and others, but in some areas I do have my own understanding which you may not agree with. Let's agree to disagree without any ill-feeling whatsoever in any quarters.

Thank you very much for your remark which I accept with gratitude and I shall be more careful in future. English being a lingua franca often leaves room for misunderstandings, more so when people from different countries and civilizations are expressing themselves in a common forum. It happens many times. So I request everyone concerned to please not feel hurt over that remark.

Thanking you and with regards to one and all,

Rajat

I guess I didn't explain my point about where one draws the system boundaries. The choice of foot fall is only illustrative of work at every joint that gets compressed and released. In order to see work being done you must make the time boundary short enough that dissipation into heat hasn't yet occurred. Because heat is not work.

Consider pushing a heavy weight across a surface. No question that this does work on the weight but by friction between the weight and the surface this whole work is quite quickly turned into heat. So if you want to look at the work, you have to ignore the interface. This also ignores the possibility that if you push the weight fast enough, you will store some work in kinetic energy which would also be dissipated when you quit pushing.

Dear James,

How can we assert that heat is not work? Heat is (kinetic) energy and change in KE energy is work, it follows that heat is work. The distinction between heat and work was resolved after kinetic theory came in but that between heat and work is carried on till today. This is central point.

In thermodynamics, PdV is work, since there is displacement, but VdP is not, since there is no displacement (change in volume), but exchange of energy and matter may be there. Is an isochoric work an impossibility? Can we not do work upon a system having constant volume? The VdP term contributes to enthalpy, which is again energy, and hence work, by the work-energy theorem. Heat and work are both the same, they energy in transit. I think this should be acceptable. The problem is the same in mechanics and thermodynamics. Examples of VdP work (work without displacement) are discussed by various authors. Similarly, in mechanics we should allow work without displacement and it does not cost us anything. It is simply a generalization of the accepted definition of work.

Regards

Rajat.

Yes, heat is NOT work, as stated by the first principle of thermodynamics: dU = Q - W

so your idea is in conflict with very well established (i.e. proven theorethically and experimentally) physics.

how could you calculate the muscle/chemical/biophysical work done by pushing on the wall ? How could you define it ?

The orbit is not circular - true the force is central - whars the problem here ?

A coolie/porter does work against the force of friction - no friction he would'nt be able to move forward

i suggest that you guys bo back to the textbooks - learn physics yourselves -

Perhaps we should return to basics and note that work is a change in kinetic energy produced by a force acting through a distance while heat is a change produced by a temperature difference. Work and heat are thereby processes, both of which can produce changes in kinetic energy, but neither of which is identified as energy.

Statistical mechanics is a different discipline than thermodynamics. Thermodynamics is a discipline of the macroscopic. As Luca has it heat and work are defined separately. PdV is not work but is one term in the statement of internal energy and is only useful in the consideration of gases. Not too well emphasized in the first course in thermodynamics is the fact that in stating internal energy, you need a term for every form of internal energy that your analysis needs. So in the case of a car going up or down a hill you need the term for potential energy, MAdx, where A is the force of gravity at the car's location, M is the car's mass and dx is the increment of height.

Perhaps also you are confusing theory and experiment. It's always true of a real world implementation of some theoretical vision that theoretically defined quantities are ideal and the real quantities in the implementation may not conform to the theory. It is up to the experimenter to see that, in the experiment set-up, defined quantities conform sufficiently to the theory as to be meaningful. Thermodynamics is one of the best supported theories in physics. The questions you raise amount to quibbles.

A few essentials for this discussion:

Thermodynamic of a System requires:

1. Definition of the System and its boundaries.

( For a person pushing a wall: one may consider just the wall, the man, the man + wall, wall + hands in contact with it.......... ) It is a non-sense calculation without well defined boundaries.

2. The choice of the transformation process of interest,

(Considering only the wall: the process is just the elastic deformation due to hands pressure........)

3. The Initial and Final states

Undeformed wall-Deformed wall

For the deformed man´s hand the situation is much more complex because it is an open system with blood flowing in and out. For the man as a whole one must consider biochemical transformations......

4. The relevant intensive and extensive variables.

The work dW on first law of thermodynamics includes all forms of work, pdV , MdH, EdP, and so on. One can calculate any generalized work (involves the product of an intensive variable, for example Pressure(P) by an extensive variable like Volume(V)). If the system of interest is just the wall, than the stress x strain relations are enough to fully describe the Thermodynamics, but the question is only partially answered.

The spendure of energy, due to Biochemical reactions is related to the effort to keep constant pressure on the wall, but provided that the pressure and therefore the deformation is kept constante no mechanical work is done ON the WALL. Measuring the consumption of oxigen, similarly to those on running effort tests, will show the energy spend by the man standing up in addition to that of pressing the wall.

For the work term associated to sun energy I would recomend a web search with kye words thermodynamics of Photosinthesys, or even first law of thermodynamics and photosinthesys

I hope to shine some light on this discussion.

Dear Rajat,

You are right that the distinction between heat, and work becomes problematic when considering the microscopic details. In chemistry we have chemical reactions and the change of energy is related to changes in the internal energy. Chemical energy provides chemical substances to undergo transformations. For instance biological information systems govern the conversion of chemical energy to mechanical energy, e.g. in molecular propellers, spindles etc. What we need is the proxy of the Helmholz free energy with its quantum analogue to understand metabolism and the emergence of functional quantum-thermal correlations and microscopic self-organization.

Dear Erkki,

I'm happy that at least one person admitted that there is some problem here. In my view, there is an unnecessary distinction being maintained from the good old days of seventeenth century science (it was not even called physics then; natural philosophy was used in stead) amongst the triad of heat, work and energy. The first law of thermodynamics establishes their equivalence, which we take as defining their difference from one another. Only energy is sufficient as the fundamental quantity. here. Work by the system is any expenditure of energy, and on the system is any receipt of energy. it can really be as simple as that.. The same applies perhaps to the various free energies, though they are all very handy in the respective problems of interest.

Rajat

Dear Rajat,

I agree with the most comments above, they are right.

Work is defined as some kind of energy in transfer, the physical content is the free energy in transfer. Yx and pV are the system states, we have the equation

d(Yx)-d(pV)=Ydx-pdV+xdY-Vdp,

where Ydx-pdV correspond to the free energy exchanges, xdY-Vdp involve the conversion between heat (include Q) and the free energy (include work W).

Indeed, Ydx-pdV and xdY-Vdp are the partial differentials of Yx-pV, so Ydx-pdV and xdY-Vdp can be combined as one term. But the physical content of work has been defined as the free energy in transfer, we ought not to change its physical content. To extend the work W to Yx-pV means that the physical content will be changed, then you will find that you cannot define Q.

Heat and work are not really basic physical quantities. One could do without. They specify energy in transit. Mathematically they are incomplete differentials, there is no heat content or work content of a body. There is no heat capacity, cp is a susceptibility. It is wrong to say, "heat is thermal energy". "Internal energy" does not allow to discriminate between different kinds of energy. The first law does not say: internal energy is composed of work and heat, it says instead internal energy can be changed by various kinds of transfers. The basic law of energy transfer is the Gibbs fundamental equation for the change of internal energy:

dE = TdS -PdV+ vdp+ fi dQ + nu dn+ ...

So heat is d Q = TdS, mechanical work is dW = -PdV and vdp (velocity times momentum), electrical work is fi dQ, chemical work ist nu dn etc. Energy can never be transfered alone, it requires a carrier: there are various extensive quantities that serve as energy carriers and associated intensive quantities, that serve as potentials or load factors for the carriers. T is the potential for the energy carrier entropy, fi is the electrical potential for the energy carrier charge Q etc. Instead of Q "heat" one should use the term "heat energy" which means the transfer of energy associated with entropy. The term "heat" should be identified instead with entropy S, which is the everyday meaning of heat. Then it is correct to talk about the heat content of a body and a heat capacity, which is a entropy capacity cp/T. Entropy understood as heat becomes a familiar concept, which is easy to comprehend even to beginners. This is the idea of KPK, the Karlsruhe physics course:

http://www.physikdidaktik.uni-karlsruhe.de/index_en.html, but goes back to Sadi Carnot. In his words entropy was called "chaleur", which flows from a high potential (temperature) to a low potential in a thermal engine, just as water flows from top to bottom in a water driven power station. Water like entropy are different from energy, they are carriers, which can release energy. I stop here.

correction: electric charge should be small q, not to be confused with Q heat.

Hi Wolfgang,

Entropy is a function of the state, or the no of possible microscopic states, which are points in phase space, which in turn is having positions and momenta as coordinates. Thus positional changes give PE and momenta changes give change in KE and thus your argument that heat is not KE, but entropy is not a rebuttal of the original proposal. Let's not keep moving round and round around the first law and come round to it yet again for any explanation or definition including the claims that heat and work are not perfect differentials etc etc. We re trying to rethink and think anew the statement of first law in view of the development in understanding macroscopic systems in terms of microscopic laws that have been discovered.

The first law is no doubt valid and has served its pupose quite well and will continue to do so in future as well. But we are trying to discuss areas which are unsatisfactory about it.

I emphasize, Internal energy is KE+PE and nothing more can be added. All these terms that you write on the RHS ad infinitum are but various forms of KE and PE only.

Regards,

Rajat

Dear Rajat,

This time I agree with you, but I think we should throw off the concept of work, other than try to redefine/augment the concept of work. Due to Q and both W are not exact/perfect differentials, KE and both PE are exact/perfect differentials. W is the free energy flux, there is another source of which, the free energy production. Heat energy is similar, Q is heat flux, another source of which is the heat production. "the flux+ the

production" can establish an exact differential.

I do this, I agree that "The first law is no doubt valid and has served its pupose quite well and will continue to do so in future as well. But we are trying to discuss areas which are unsatisfactory about it".

Please see the paper, eqs.(8), (10), (47) and (48).

https://www.researchgate.net/publication/236983852_Internal_Heat_Energy_Entropy_and_The_Second_Law_A_New_Approach_to_Theoretical_Thermodynamics_(v4)

Data Internal Heat Energy, Entropy and The Second Law: A New Pers...

hi Rajat,

you ask whether "work" is adequately defined in textbooks. I think yes, if it is defined as a nonthermal transfer of energy. This includes also gravitational, electrical, magnetic and chemical energy, even in the absence of displacements. Thus all transfers count as mechanical which do not involve the transport of entropy. Someone holding up a weight does not do any work, since no energy is transfered to the body, although some chemical energy in his muscles is converted to heat involving the creation of entropy. What I was trying to point out, obviously without success, was that one could do perfect physics without using the terms work and heat. Thermodynamics can be derived from the Gibbs fundamental equation (Callen, thermodynamics) which does not contain work or heat. One should not confuse thermodynamics with statistical mechanics, which are different concepts sharing a common ground. When external energy is converted to internal energy, it becomes kinetic and potential energy, but also electrical, chemical and magnetic energy, which cannot be separated within thermodynamics. Work is a popular physical concept like heat, which seem deceptively simple. Confusion often arises, since the physical quantities are different from their meaning in everyday life. Finally: The first law looks like a definition of internal energy. But its true meaning is that it postulates the existence of an energy state function. With the exchange of heat and work one can explore this function. Greetings.

Thank you Tang for the reference to your work.

The very idea of having the concept of work stems from our daily performance of various forms of work. It is only when science, especially, physics, tried to disentangle itself from any reference to the conscious living beings that work was assigned to non-living, non-intelligent forces of a non-intelligent Nature. The reason was that living beings are too hot to handle in science , life sciences notwithstanding !

Thus emerged classical objective science without supposedly having any reference to consciousness, which was proclaimed aloud to be a latter emergence or evolution from its non-living material roots. This continued for a few centuries before QM forced us to rethink.

Any way, that is not the point here. It came because historically the assignment of work directly to a causative force rather than to a conscious causative agency behind the force, is a very great departure indeed. Therefore, it is not surprising that we do not find it easy to get rid of any of the entrenched ideas even if presented with glaring shortcomings and drawbacks.

It is good to see that people like you are taking a relook at the established laws.

Regards,

Rajat.

Thanks a lot Wolfgang for your clarifications. I am not calling for abolition of the concept of work altogether. I am just advocating an augmentation of the definition to include all kinds of energy transfer to and from the system. It is a s simple as that. If a force and a displacement are involved well and good. If not, work can still be done through energy transfers. Heat is any way already accepted as a form of energy and we have no problems with that.

Regards,

Rajat

Truth is that most of the people who have earned good grades in physics, are totally unwilling to consider alternatives to the well established concepts. Whenever someone advocates that well-established concept will never need reconsiderationl, is not doing justice to science. Pity that this unwillingness is often seen in physics classrooms, in the front of the room... .

Yes. You are right Eddy.

Thank you very much.