All Questions
15
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How are Shannon's non-physical entropy and physical entropy related?
Suppose there is a die manufacturer. This facility has a dice machine which is in charge of producing new dice by casting their faces in molds made out of some special material, so in a way, it has a ...
- 91
-1
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2
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487
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What are some examples of microscopic quantities?
Mass, volume, energy, entropy, temperature, pressure are some macroscopic quantities. Which means we can think of them even without considering the molecular nature of matter.
What are some examples ...
- 521
1
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1
answer
105
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Why is it said that entropy of a closed system may increase in classical physics?
Why is it said that entropy of a closed system may increase in classical physics?
A classic thought experiment to explain this claim is that of a closed box with some moving billiard balls initially ...
- 676
4
votes
2
answers
409
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How to fully understand the Definition of Entropy?
In the context of Thermodynamics and Statistical Mechanics we encounter, basically, three different definition of entropy:
First definition:
Consider an isolated macroscopic system, it has a ...
- 4,577
-3
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1
answer
124
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What if 1st law of motion and 2nd law of thermodynamics contradict?
Assume a large flat surface with a pile of books on it somewhere. Assume this system to be isolated and gravity to be present there. Also assume there to be a flow of time.
As now you have ...
- 119
2
votes
1
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788
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Time derivative of Gibbs entropy (the paradox of the constant fine-grained entropy)
In the context of classical systems, the fine-grained (or Gibbs) entropy is defined as the functional:
$S_G(t)=-k\int_{\Gamma_t}dqdp\ \rho(p,q,t)\ln[\rho(p,q,t)]$ (1)
I've been told (Wehrl and J. van ...
- 1,091
2
votes
2
answers
116
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Is the entropy of a rotating body largest when the axis of rotation passes through it's centre of mass? [closed]
I am looking for an answer to the observation that a body always rotates about its centre of mass when freely tossed. It can be explained if the entropy is highest in the case when the axis passes ...
- 21
3
votes
1
answer
677
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Collision Term in the Classical Boltzmann Transport Equation
I cannot get over the feeling that in the classical derivation of the collision term of Boltzmann's transport equation molecules that are already knocked out of a $(\textbf r, \textbf v)$ space volume ...
- 31
8
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1
answer
828
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Entropy and classical mechanics
I was trying to understand what entropy means in the context of classical mechanics, but unfortunately I'm now more confused than I started. Reading, for example, the Wikipedia article on the Second ...
- 661
2
votes
1
answer
2k
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Microcanonical and canonical ensemble entropy comparison in Einstein solid
Consider Einstein solid model ($N$ oscillators of same frequency $\omega$, where $n=\sum k_i $ with $k_i$ being the occupation number of single oscillators)
In microcanonical ensemble entropy is
$$S=...
- 2,617
2
votes
0
answers
81
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Entropy before and after sampling an ideal gas
Suppose I have N ideal gas particles of unknown types, but they have the same mass. I then sample a negligible number of particles and conclude I have actually have 3 different colors of particles. ...
- 151
3
votes
3
answers
814
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Why is entropy defined the way it is in classical thermodynamics?
Entropy as defined by the Clausius statement in classical thermodynamics, is only defined for equilibrium states.
I do not understand why is the definition restricted to equilibrium states. Would an ...
- 1,466
2
votes
3
answers
512
views
Does the second law of thermodynamics take into consideration of attractive interactions between particles?
If one searches Google or textbooks on 2nd Law of Thermodnamics, one usually finds a statement that is either equivalent or implies the following.
The entropy of the universe always increases.
But ...
- 589
7
votes
2
answers
714
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Why doesn't a Brownian ratchet provide free energy?
A Brownian ratchet is described here at Wikipedia.
The "why it fails" section reads:
Feynman demonstrated that if the entire device is at the same temperature, the ratchet will not rotate ...
- 343
2
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1
answer
378
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Do all closed systems, only considering kinematic/mechanical principles, exhibit time reversal symmetry?
It makes a lot of sense to me to imagine a cannonball flying through space as not so much experiencing a macroscopic non-conservative drag force, but as pushing a bunch of air molecules and giving ...
- 6,000