6:26 AM
@EmilioPisanty unfortunately that user has done nothing except copy from paleotechnologist.net/?p=231 verbatim
...and received 8 upvotes for it (though of course, the upvoters would not have known this)
their second "question" on the site is another such specimen, this time from a ResearchGate Q&A

1 hour later…
7:53 AM
@NiharKarve ah, thanks for the pointer. That changes everything. Please flag it as plagiarism.

2 hours later…
9:23 AM
Hi All..
Hello @JohnRennie Sir..
What is the need of zeroth law of thermodynamics, what it tell us special about temperature? Also i have read many threads and in books about it but it is not very clear to me. like;
1) Zeroth Law is the transitive equality property of temperature. It means reflexive, symmetric and transitive property of temperature satisfy with three different objects if they are in thermal equilibrium. "Why do we care about care about transitive equality property of temperature" . Also 1st and 2nd law of thermodynamics gives us asymmetric relation of temperature.
2) Also zeroth law allow us to create different scale of thermometers with empirical temperature measurement on the basis of their thermometric properties. "I don't see how zeroth law enable to to create any kind of thermometer".
Pls help me to figure this out.

@123 A thermometer measures temperature by equilibrating with the system whose temperature you want to measure. The zeroth law tells you that if a thermometer shows the same reading for different systems, then these systems really have the same temperature: The transitivity means that because both systems are in equilibrium with the thermometer at the same reading, both systems also arein equilibrium with each other.
if thermal equilibrium was not transitive, the thermometer showing the same reading for different systems wouldn't really tell you anything

9:43 AM
Hello @ACuriousMind
@ACuriousMind It means transitive property of temperature guarantee us that as temperature are equal they are also in thermal equilibrium. "But how we know thermal equilibrium and temperature are related". What is the guarantee of it.

What do the quotation marks in your message mean?

Quotation mark means this is question i asked.

That's...not what quotation marks are for (question marks are for questions!), but anyway: What's your definition of temperature that you want a "guarantee" here? Usually one defines temperature as a common property of all objects that are in thermal equilibrium with each other.
the zeroth law guarantees that this actually makes sense as a definition

@ACuriousMind Oooh Ookay.. Why science is so deep and confusing :-) .
At first we understand temperature on the basis of our sense of hotness or coldness.
Now we define temperature as common property of all object when they are in thermal equilibrium. It means once again we should define what is thermal equilibrium. There could be many other properties which can be same in thermodynamic systems like pressure, volume. In my view thermal property must be specific to how we measure it.
How do we distinguish between temperature and pressure on measurement? How they are different properties of thermodynamic system?

10:14 AM
You measure temperature with a thermometer
You measure pressure with a pressure gauge
If we go purely by operational definitions
You can check that some systems have the same temperature but different pressure
and vice versa

@Slereah Yes but one confusion is that do temperature and pressure are completely independent properties or they are related?
If they are related like PV = nRT , Then how at same temperature we can have different pressure and vice verca.

Who is in your se dp?@ACuriousMind

They are independent in the sense that you can have systems of unrelated pressure and temperature
But they are related by the equation of state of the material you have
but that depends on the material

Zeroth law says thermal equilibrium is an equivalence relation, thus one can say that all objects in the same equivalence class have the same 'temperature' if one defines a temperature function on the space of equivalence classes of objects under thermal equilibrium

Thermodynamic is too much confusing subject. There is no systematic way of the subject. One term can be used in many many ways and sense. Like internal energy etc.. Which makes subject worst.

10:24 AM
@123 chapter 4 here is a good summary of a basic thermo discussion, the other chapters are on the stat mech perspective

@bolbteppa How do we know and sure about thermal equilibrium exist. because it is based on measurement of temperature. and temperature measurement based on thermometric property of material (e.g: mercury thermometer its volume change with temperature change). So what is it?
There should be some clear line and distinction between temperature and pressure. So we can easily understand the both properties of system separately. I didn't find it.

What is the Indian variant(INSA-COG) E484Q and L452R?

Temperature is not defined until you first define thermal equilibrium: "An isolated system with a time-independent state is said to be in equilibrium", we can then say two isolated systems are in T.E. with one another if when they are brought together T.E. remains. Zeroth law just says the obvious that this is naturally an equivalence relation. We can then define a function called temperature which gives the same value for every element in an equivalence class.

How are mutations named does anyone have any idea?

We can clearly use any invertible function or a composition of functions to define temperature thus we can define different temperature scales (as those notes point out)

10:39 AM
@bolbteppa Great it is sort of satisfactory answer. Thanks
@bolbteppa there could be many different properties is same in equilibrium which we can define. Why zeroth law focus about only temperature.

It's just a number we associate to objects that lets us interpret some objects as hotter/colder than others

May be if we have one isolated system cup of tea in equilibrium with thermometer and we have other system gas cylinder also in equilibrium with thermometer. May be they can have temperature common but not other properties like pressure, volume etc.. If this is the case we rely on thermometer for thermal equilibrium.

Yes it's not the only thing we can say about a given system, it's just one of a few different things we can say
The question is, why is it enough e.g. to just talk about say temperature and volume for a system, this comes down to the fact that energy, volume and entropy are additive quantities

@bolbteppa Temperature and pressure are specific way of measuring properties of system.
I have read in Wikipedia for state function and state variable. They define temperature, pressure and volume are state function and also state variable. What is that mean?

11:07 AM
[text](link)

The idea is that, for a closed isolated system at rest, the energy, which is additive, only depends on the entropy in the form $dE = T dS$ where $T$ is the temperature. If we allow the body to interact with things outside it in such a way that only the external conditions are allowed to change, it means that the external conditions can now either affect the overall volume of, or pressure on, the object. Since volume is additive we now have $dE = TdS - P dV$, where the last term can be justified

@bolbteppa You have share good lectures above. Which is part II if you have part I pls share it.

When a closed isolated system interacts with the external system in a way that changes only the external conditions, it's not actually closed any longer obviously, it's now called thermally isolated, now things like energy and volume can change, additive quantities, so they can be interpreted as affecting the entropy (additive)

@bolbteppa Good explanation. So that's how it become First law of Thermodynamics. This kind of explanation i was looking in books.

So one of the additive quantities in $(E,S,V)$ is determined by two of the others, from this we can interpret e.g. $T$ as a dual variable to $S$, or $P$ as a dual variable to $V$, so the choice of variables is in a sense arbitrary, any two fixes a third variable for a thermally isolated system at rest a state function is a function of any two variables fixing the state of the system
This is all the classical thermodynamics perspective on thermal equilibrium. From a statistical perspective one can interpret thermal equilibrium as saying that the value of some quantity you measure for the system is largely equal to the mean value, where one obviously has to define taking a mean value carefully, and one can then define entropy statistically and then other quantities like temperature in terms of entropy,
almost backwards from the classical themo perspective where entropy is introduced near the end!

11:22 AM
@bolbteppa Thanks a lot.
@bolbteppa In this link Pls clear the point 1.) What is system at rest. (2) What is additive energy means.

Additive means if we take a system to be composed of two subsystems of energies $E_1$ and $E_2$, the total energy of the combined system is then $E_1 + E_2$ and not $E_1 \times E_2$ or something. At rest means the system has no overall momentum $\mathbf{P}$ or angular momentum $\mathbf{M}$, these are also additive quantities in the same sense as for energy $E$, for a moving thermodynamic system one can obviously introduce these variables.

If system has additive energy (does it interact with outside or not) where this energy comes from?
Where this energy comes from. Is it the energy of system itself at any state which system can have or it comes from external source?
@bolbteppa It means if external energy only change entropy it is responsible for change in temperature. also this external energy can only change the volume and pressure. Also this external can do both thing entropy and pressure/volume change at the same time? Am i correct and this make 1st law of thermodynamics.

For a closed isolated system the energy is additive in the sense that if we think of the closed isolated system as composed of subsystems with energies $E_i$ the total energy of the overall system is $E = \sum_i E_i$. Not talking about any interactions with the outside here. The energy obviously comes from the particles making up the system.
Note above I said interactions with the outside are then introduced as ones which only change the external conditions, this means only e.g. the volume of the system can change, or so that energy can pass in and out, but the system e.g. does not melt or evaporate and stop being a system interacting with the external environment

11:43 AM
@bolbteppa Oooo.. Yes that why confused once i read it is closed isolated system then additive energy. Now it is clear it is the energy of particle which make up the system.
Pls clear 1st law of thermodynamics. U = Q + W what is internal energy here, heat and work.
Work i assume any change in volume or pressure by external interaction/ thermodynamic operation. What heat does here which is also related to boundary of system as work but it is not clear also what is internal energy?

It's in chapter 4

U = Q + W ; dU = dQ + dW
@bolbteppa I am reading chapter 4 it is good explanation, not complete read yet.
Pls clear what is internal energy U means in 1st law of thermodynamics. Does it same which you explained above it is the energy of particles which make up the system?

@bolbteppa which book are you guys discussing?

Yes
@satan29 I linked to notes above

@bolbteppa Is there also any book which explain classical thermodynamics in great detail with each single term and processes clearly.

12:00 PM
Those notes and
Fundamentals of Physics is a calculus-based physics textbook by David Halliday, Robert Resnick, and Jearl Walker. The textbook is currently in its eleventh edition (published 2018). The current version is a revised version of the original 1960 textbook Physics for Students of Science and Engineering by Halliday and Resnick, which was published in two parts (Part I containing Chapters 1-25 and covering mechanics and thermodynamics; Part II containing Chapters 26-48 and covering electromagnetism, optics, and introducing quantum physics). A 1966 revision of the first edition of Part I changed the...

The book which explain physics way and also mathematical way. It may by more than one book.

or something similar like H.C. Verma

wow, you know about HC verma?

I have read fundamental of physics by halliday, resnick. I don't like this book there is no detail and satisfactory explanation of any of the physics topic. Also i have read HC verma. Both are not reach the satisfactory level.

This is why people study the statistical mechanics interpretation of classical thermodynamics

12:04 PM
Like in mechanics i found Kleppner Kolenknow best for introductory, symon mechanics at advanced level. I am searching for this type of book in thermodynamics. I share you books what is have pls help me and suggest names.
1drv.ms/u/s!AozWlUoG8z4tngqTUV7JZk6aD1Q6?e=asNk13 Pls see my inventory of thermodynamics books.

Another idea is some engineering thermodynamics books, but I'd recommend just doing the simple versions then doing it all properly with statistical mechanics

@bolbteppa I have started to read engineering book line cengel, shipparo but i found engineering books are always superficial to the topic. They just explained the phenomenon not basic science explanation.

The Course of Theoretical Physics is a ten-volume series of books covering theoretical physics that was initiated by Lev Landau and written in collaboration with his student Evgeny Lifshitz starting in the late 1930s. It is said that Landau composed much of the series in his head while in an NKVD prison in 1938-1939. However, almost all of the actual writing of the early volumes was done by Lifshitz, giving rise to the witticism, "not a word of Landau and not a thought of Lifshitz". The first eight volumes were finished in the 1950s, written in Russian and translated into English in the late 1950s...
Volume 5 has the best explanations but it's also one of the hardest
You have to ask yourself, why in those Halliday books do we go from Newtonian mechanics to systems of gigantic numbers of degrees of freedom and then basically ignore Newtonian mechanics

@JackRod Iosef Lilianovich Dros.

@bolbteppa :P i have tried to read Landau but it is harder than my level of understanding. First i want to read book which explain thermodynamic phenomenon in detail.
@bolbteppa You are right. Because at atomic and molecular level we can have more better understanding of physical phenomenon. I have read statistical mechanics 3 years ago. I understand basic principle of that.

12:28 PM
"Every mathematician knows it is impossible to understand an elementary course in thermodynamics." - V. I. Arnold
3

@bolbteppa :D right . Arnold Somerfield

2 hours later…
2:31 PM
Hello @JohnRennie Sir..

3 hours later…
5:10 PM
How only position and velocities of particles completely define the path of rigid body without knowing the force?
If we know the force we can find path using integral rule. but position and velocities completely define the path without force.

@123 what's the question verbatim?
Like what is this rigid body?

@JohnT. I read in book knowing position and velocities we can find the path,

What is the rigid body? Is it an object in space?

@JohnT. yes

Well then the only force is that of gravity
Which you know to be $F_g = \frac{G m_1 m_2}{d^2}$

5:16 PM
We can use this simple case. But book did not specific to the gravity.
I have read only position and velocity can define the path of body. It means don't need information of force. How it is possible

Maybe it's talking about path being defined in terms of position and velocity
but velocity can obviously change due to a force?

@JohnT. I know by force we can find path. but without force only by knowing position and velocity how we know the path
As in lagrangian configuration space we take only position and velocities.

I have a problem, which I think is far too simple for a question, but for some reason my head isn't quite working and I'm not confident in my answer. We're working with electrostatics. Suppose we have a sphere with some total charge +q, surrounded by a spherical conducting shell with no charge, all of which is enclosed in a third shell with total charge -q. We want to graph the electric field along a radius.
Outside the third shell, wouldn't the E-field just be 0?
And then, between the inner charged sphere and the outer charged shell, it would simply fall as 1/r^2 (except for 0 E-field inside the uncharged shell).

@KeithMadison Is the radius just from the center of the inner shell to the outer shell?
If so, you wouldn't need the e-field beyond that point.

@JohnT. I'm asked to sketch it from the centre of the inner charged sphere to a "short distance" outside of the third, outer shell

5:31 PM
Okay, so you have (-q (0 (+q | +q) 0) -q) so you need to figure out what the e-field between the shells are, the e-field in the inner shell, and the e-field right outside the outer

Lets see. The E-field in the inner, conducting charged sphere is 0, since it's at electrostatic equilibrium. Using Gauss law, the charge of the outer sphere doesn't matter until we reach it. So, the E-field will fall as 1/r^2 from the outer surface of the inner charged sphere to the inner surface of the outermost charged shell, except when it is zero between the inner/outer surface of the inner, uncharged shell.
Then, the E-field inside the outermost shell is zero, and outside of the outermost shell it will be... 0? Using Gauss law, since charge enclosed = (+q) + (-q) = 0.

5:50 PM
sorry I had to go for a moment, @KeithMadison Yes that sounds about right assuming they're equidistant from each other, but don't they want your answer in the form of math?

@JohnT. Got it, thanks! No, I need only draw a rough sketch of what the graph of E vs distance from the centre along some radius looks like.

For example, the electric field of the Gaussian surface from the inner shell would be $E_{in} = \frac{Q_{in}}{4\pi R^2 \epsilon}$
Ah okay
Also note that the E field of a point within the outer shell is given by the ratio $E = \frac{Q_{out}r}{4\pi \epsilon_{0}R^3}$
Ratio of volumes of the Gaussian surface of radius r and the outer shell that is