# What is Thermodyamics: Definition and 265 Discussions

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1. ### Why does this question make this simplifying assumption?

The question says to "neglect the change of volume of the water". This confuses me. Why do we neglect the change of the water's volume? Let's say we didn't. A = Q/It, where A is area, Q is heat, I is intensity, t is time. Q = mc(deltatheta), mass is constant, specific heat is constant (as mass...
2. ### A Symmetry breaking in the AdS small/large black hole phase transition

I am trying to reproduce the results from this paper where they find out the expression for the Landau functional to be $$\psi(x,t,p)=\frac{1}{4}(\frac{1}{x}+6x+px^3-4tx^2)$$ We plot the Landau functional v/s the order parameter($x$) at $p=0.5$ and obtain the Figure 4. from the paper as Now...
3. ### I Could entropy be reversed eventually in the far future?

In the far future there will be most likely a point where a maximal state of entropy will be reached in the universe and after the last black hole evaporates there could be no more structures and no more work could be done. According to the Poincaré recurrence theorem for a closed universe...
4. ### Mixing two gases in an isolated system and calculating final p and T

Hey everyone, I have an attempt at fully solving this problem (my final pressure is ##p_f = 5373,64 hPa##, final temp. is ##T_f = 303,15K = 30C##), but this exercise confuses me very much. First, I have not used the masses in my calculations and I'm pretty sure my prof. accidentally copypasted...

I was unable show that ##PV^k## must indeed equal some function of the entropy, ##g(S)##; maybe doing so would make things easier? I proceeded as below. If we assume (as is almost surely intended by Callen) that in the given adiabatic (##d Q = 0##) process we are taking ##N## as constant and...
6. ### I Disproving Carnot's Theorem: Is There an Error in My Thinking?

But if I would assume that the efficiency of the carnot's engine is greater than the other engine and the carnot engine is driving the other engine backward as a refrigerator ,that would lead to the same contradiction hence disproving carbot's theorem! Is there something wrong I have done...
7. ### I Heating gasses in space -- How could we make a greenhouse in space?

I was thinking the other day about green houses and how they would act in space or on another planet without an atmosphere. I know that green houses work on Earth by stopping convection but could they theoretically trap heat in a non atmospheric environment? I am imagining a material that allows...
8. ### I Mining the Universe's expansion?

There is an article written by astrophysicist Edward Harrison [1] which defends that energy could be extracted from attaching an imaginary cosmologically long string to a receding object from us in an expanding universe. He says that the energy extracted is potentially limited (in decelerating...
9. ### I Would infinite entropy break all symmetries?

If the Universe could somehow reach a state of infinite entropy (or at least a state of extremely high entropy), would all fundamental symmetries of the physical laws (gauge symmetries, Lorentz symmetry, CPT symmetry, symmetries linked to conservation principles...etc) fail to hold or be...
10. ### I About Reversible vs Irreversible Gas Compression and Expansion Work

Hi, reading the interesting Reversible vs Irreversible Gas Compression and Expansion Work insight by @Chestermiller I would like to ask for clarification on some points. In the second bullet at the beginning my understanding is as follows: consider an ideal gas contained in a cylinder...
11. ### Cooling a marine engine while testing

For my internship I have to test and certify a Marine diesel engine. We are trying to run a few tests in our workshop, but this obviously means we can't use the sea or a river as cooling. We bought an IBC tank, which can hold a 1000 liters of water. The water from the tank will be running...
12. ### Calculating specific heat capacity from entropy

Hey guys! I'm currently struggling with a specific thermodynamics problem. I'm given the entropy of a system (where ##A## is a constant with fitting physical units): $$S(U,V,N)=A(UVN)^{1/3}$$I'm asked to calculate the specific heat capacity at constant pressure ##C_p## and at constant volume...
13. ### Find change in entropy for a system with a series of reservoirs

I've calculated the change in the entropy of material after it comes in contact with the reservoir: $$\Delta S_1 = C \int_{T_i+t\Delta T}^{T_i+(t+1)\Delta T} \frac{dT}{T} = C \ln{\frac{T_i+(t+1)\Delta T}{T_i+t\Delta T}}$$ Now I would like to calculate the change in the entropy of the...

50. ### Work on a compressed gas

Homework Statement What is w when a gas is compressed from 42.1 L to 25.1 L using a constant external pressure of 739 Torr? Remember to include a "+" or "−" sign as appropriate. Homework Equations W = -P(dV) The Attempt at a Solution Pressure = (739 Torr / 760 Torr)*(101.325 kPa) W =...