Covers the study of (mostly homogeneous) macroscopic systems from a heat/energy/entropy point of view. Maybe combine with [tag:statistical-mechanics].

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Minimisation of thermodynamic potentials?

An alternative formulation of the second law is that the energy of the system $U$ is minimised if the temperature and entropy of the system are held constant. However, $$dU=TdS-pdV$$ which means ...
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30 views

probability of striking the circular ring by gas molecules

In kinetic theory we use probabilistic case to derive pressure, no. Of molecules having speed c to c+dc or in such cases.and to derive such equations we introduce a term called "SOLID ANGLE" I come ...
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3answers
2k views

Why does water feel cooler than air?

My first assumption was based on "evaporation causes cooling" but I realized that it is not the case as it is cooler even if I am submerged under it. Are all liquids generally cooler than air ? Just ...
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1answer
52 views

Reversible process, equivalence of two definitions?

There are two common definitions of a reversible process: A reversible processes is quasistatic with no dissipation. And A process where an infinitesimal change in conditions would reverse ...
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2answers
40 views

Adiabatic expansion on $(P,T)$ diagram

Consider a certain substance which is described by pressure $P$, volume $V$ and temperature $T$. In one thermodynamics exercise I was asked to draw one adiabatic expansion from $V_1$ to $V_2$ in a ...
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13 views

How the degrees of freedom for gas molecules affect energy

It seems a bit unclear to me how degrees of freedom help judge the amount of kinetics energy in the system. from the formula for the energy of molecule ε = u0 + (v/2)kT it can be inferred that the ...
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4answers
134 views

Ice in contact with a heat reservoir at $0^\circ \textrm{C}$?

Let us say I put ice starting at a temperature $T \lt 0^\circ \textrm{C}$, and held at constant pressure of $1atm$ in contact with an infinite heat reservoir at temperature exactly $0^\circ ...
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1answer
900 views

What leads to the existence of critical temperature?

We know that $T_c$ is the temperature above which no amount of pressure could force a gas to liquefy. But why is this? Somehow I don't buy the point that the gas molecules exert too much pressure ...
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2answers
48 views

What is the minimum energy a quantum can bear? …and more

Here are my assumptions: Energy can be transferred only in limited dosages. When two particles collide, they exchange energy, so that the more energetic particle carries less and the less energetic ...
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1answer
21 views

Derivation of Internal Energy of an Ideal Gas

I have so far derived that $$E_K= \frac{3k_BT}{2} $$ where $E_K$ stands for the average random kinetic energy possessed by particles of an average gas. Now we can take one step further by using this ...
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23 views

Calculating heat distribution along 1D line segment?

I want to calculate temperature distribution where the heating power of $P_0$ is uniformly distributed over 1D bar TO calculate, there is heat equation. $$ \frac{\partial T}{\partial ...
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1answer
32 views

How the mechanical equivalent of heat is employed in this situation?

Reading a little about the "mechanical equivalent of heat" what I understood is that we can convert units between calorie and $J$ by setting $$1\mathrm{\ J} =4.1860 \mathrm{ \ cal}.$$ Now, I saw a ...
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27 views

Energy inside a box of air with temperature variation

How to find the energy of a column of air enclosed in a box (assume adiabatic) with a temperature variation $T(z)$ in the vertical ($z$ direction) in a uniform gravitation field? I think the total ...
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0answers
37 views

Why do different color materal differ temperature in the same sunlight?

I have a blue, red, and green cup and put a thermometer in each. Of the 3 the blue cup had the coldest temperature inside, then green, then red. I understand there may be differences in the ...
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0answers
51 views

Radiative equilibrium in orbit of a black hole

According to Life under a black sun, Miller's planet from Interstellar, with a time dilation factor of 60,000, should be heated to around 890C by blue-shifted cosmic background radiation. How they ...
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1answer
28 views

Can a piston-like displacement be miscible?

I have a question regarding miscibility and piston-displacement of fluids. My question is as follows: I am given that a fluid is displaced miscible. At the same time, I am also given that the ...
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0answers
24 views

Relations between Maxwell-Boltzmann's distribution and the n-body problem velocities distribution

Solving the n-body problem numerically and finding the velocities distribution, one finds that it's quite similar to Maxwell-Boltzmann's velocity distribution. This is quite suprising because of the ...
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0answers
30 views

Confusion about the number of micro states and approximating it for large number of particles

Hopefully after reading the meta site, I can now rephrase the question as more relevant to this site, this is a question related to statistical physics: Let us suppose we are given a system with ...
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1answer
83 views

Ultraviolet catastrophe in a classical world

In the real world, the ultraviolet catastrophe doesn't happen because the quantization of photons modifies the classical behavior of light at frequencies comparable to and higher than the temperature. ...
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1answer
41 views

Gas/liquid pressure equilibrium of water in an exotic environments

So I'll preface this by saying this is not some evil homework assignment, this came about from some idle talk of colonizing the moon by a couple of software engineers when we realized we had no idea ...
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2answers
39 views

Emissivity and Final Temperature of a Black and White object

Objects can be categorized as blackbodies (emissivity $\epsilon = 1$), grey bodies (emissivity $\epsilon < 1$) and white bodies (emissivity $\epsilon = 0$). If we placed two objects (identical ...
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3answers
101 views

How is pressure kept constant in Charles' Law?

Generally, a piston is kept on top of a cylinder containing the gas. The gas is heated and it expands causing a change in the volume. I was wondering how might one keep the pressure constant. Websites ...
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1answer
103 views

How to make Temperature vs. Energy graph representing a phase change?

As we know that phase change graphs generally show a variation in the Temperature and time.The graph roughly looks like this. I guess that the shape of the curve will be the same. This is because ...
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0answers
46 views

Carnot Engine- Cold Reservoir is a black body [closed]

My question: A satellite powered by a Carnot engine uses heat from a nuclear reactor at a fixed temperature T0. Heat is released into outer space via thermal radiation emitted by a set of fins at ...
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1answer
23 views

Clarification regarding Homogenous systems in Thermodynamics

So i have just started with Classical Thermodynamics..and i am reading Thermodynamics by Bruno LinderSo I could not understand what he means in this portion- If intensive properties are uniform ...
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1answer
225 views

What prevents this magnetic perpetual motion device from working? [closed]

Two days ago, I thought of this device, which may seem to rotate indefinitely(in all 3 directions). I have two questions. Is this perpetual motion machine already known? If it is, could you please ...
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1answer
173 views

Melting ice: reversible or irreversible?

I am looking into whether the melting of ice (or any substance for that matter) at constant pressure and temperature is reversible or irreversible. Different sources say different things, and it may ...
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0answers
25 views

Is frictional heat just electromagnetic interactions creating infrared radiation?

Example: Rub your index finger on a sheet of paper and you will feel that it will get noticeably hotter Is the reason you feel this increase in heat (technically an increase in kinetic energy of the ...
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2answers
54 views

How is rate of cooling of a body related to its Volume?

I was wondering how two bodies made of the same material and having the same Surface Area but different Volumes, heated to the same temperature, would cool. Would they cool at the same rate? I know ...
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1answer
49 views

In the Nernst equation $E=E_{cell}-\left(\frac{0.0592V}{n}\right)\log Q$, what does the $E_{cell}$ represent?

In the Nernst equation $$E=E_{Cell}-\left(\frac{0.0592V}{n}\right)\log Q$$ what does the $E_{cell}$ represent? I read that $E_{cell}$ is the standard state condition of the cell, let us say that we ...
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1answer
51 views

Entropy generation during irreversible adiabatic expansion

During irreversible adiabatic expansion entropy is generated. It means that the gas expands to as greater volume than that during reversible adiabatic expansion for the same change in pressure. How ...
4
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1answer
51 views

Is osmosis a kind of thermal machine?

The hyperphysics article defines osmosis as a process driven by internal energy and internal energy is defined as energy associated with random,disordered motion of molecules. Osmosis develops ...
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0answers
27 views

processes that cause heat loss in buildings [closed]

I'm looking for a fair study in which they assessed the importance of different processes that cause overall heat loss in buildings. With processes i mean convection, radiation, conduction trough the ...
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0answers
24 views

Ratio of Stagnation to Normal Flow Properties in Incompressible Flows

I know in compressible flows the ratio of stagnation to normal flow variables is a function of the Mach number and usually the specific heat ratio. Does this ratio mean anything for incompressible ...
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19 views

How does heat conduction differ from convection? [closed]

How does heat conduction differ from convection?
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2answers
36 views

Why does the temperature of the gas in a container moving with constant velocity not change?

Systematic changes do not affect thermodynamic equilibrium. What does this mean? And what kind of systematic changes are allowed? The container with gas is stationary till some time then it's ...
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2answers
50 views

How to see intuitively that $\kappa_T$ is constant for solids?

In thermodynamics we define $$\kappa_T = -\dfrac{1}{V}\left(\dfrac{\partial V}{\partial p}\right)_T.$$ By this definition, if we are treating $V$ as a function of $p$ and $T$, then $\kappa_T$ is ...
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0answers
25 views

How do I compute mass flow rate for a compressible fluid?

Consider the vacuum chamber in the figure. If a hole with cross section area $A_{cs}$ is created, how can I approximate the maximum mass flow rate, $\dot{m}$, for a compressible fluid (e.g. air)?
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1answer
69 views

Water vs. Air : Heat Absorption/Capacity

I am not a physicist by any means and not even a current student, but nonetheless I am looking for an answer. Here is what I have gotten so far from university websites and other various resources on ...
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0answers
74 views

Might the zero point of the Kelvin scale been mislocated? [closed]

This is fundamentally a thermodynamics question, but it has ties to cosmology and the temperature of the cosmic microwave background (cmb). Since T(cmb) ~ 2.725 K it brings up a comparison with the ...
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0answers
16 views

the physics of absorbing a laser's beam through contact of mirrors [closed]

If you were to set out multiple mirrors or even double sided mirrors how many Times would it have to reflect to be completely absorbed into heat by the lasers??
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1answer
31 views

The effects of heat and work on a system

I am unable to grasp the following statements which I found in the literature. For a closed system (no transfer of matter), heat in statistical mechanics is the energy transfer associated with a ...
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0answers
36 views

Energy dissipation in spinning wheel

I was given the following question in a test. A spinning wheel A is brought in contact with an identical wheel spinning at identical speed.The wheels slow down under the action of friction.Which ...
4
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2answers
66 views

Difference between two types of pressure

When I first studied thermodynamics the concept of pressure was defined by means of the fundamental relation $S = S(U,V,N)$ for simple systems. The pressure was thus defined by $$P = ...
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0answers
49 views

Is it possible to consider PV diagrams without the equations of state?

Suppose that we have the equations of state for a particular system, or equivalently, that we have the fundamental relation $S = S(U,V,N)$. If we want to write down a PV diagram it will be quite ...
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1answer
73 views

Would it be possible that a broken glass can return to its original state spontaneous at 0K?

my teacher said that a broken glass can't fix itself spontaneous because of the second law of thermodynamics, entropy won't decrease in a isolated system. But when the temperature is at 0k, then ...
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0answers
15 views

Temperature of throttled flow

In a pipe with a throat, closed off to the left, I'm pouring in $\dot{n}$ atoms per second from the left. These atoms combine and do a chemical reaction, which releases energy. To the right, past the ...
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1answer
25 views

Velocity of flue gas

I was wondering on how to calculate velocity of a flue gas which has a gas molecular weight of 28.1544, density of 0.0268 (lb/ft$^3$), temperature of 980˚F, specific heat of 0.2805 (Btu/lb-F), and ...
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1answer
49 views

Density solver for ideal mixture of real gases

I am referring the paper on GERG-2008 equation of state. I am interested in calculating the properties of ideal mixtures of real gases. The GERG-2008 EOS is in Helmholtz free energy and hence the ...
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2answers
52 views

Why are metals worse conductors when heated?

When metals, (such as in circuits), are heated, their ability to conduct electric current is hampered. Why is this? Does the transition towards liquid disrupt a metal's ability to conduct, or is ...