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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Rotational Constant and Moment of Inertia of Fluorine gas

I have come across some homework question on thermodynamics which needs me to calculate $B$ of $F_2$ My attempt: $B= \frac{h}{8\pi^2cI}$ where $I=\mu r^2=\frac{m_1m_2}{m_1+m_2} r^2$ Atomic mass of ...
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105 views

Is there a relation between supersymmetry and entropy?

Considering that entropy denotes the level of order/disorder in a system, would it be possible for entropy and supersymmetry to exist at the same time? Or, are they entirely unrelated?
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672 views

Why isn't the Bekenstein-Hawking Entropy considered the quantum gravitational unification?

Based on the Bekenstein-Hawking Equation for Entropy, hasn't the relationship between quantum mechanics and gravity already been established.
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729 views

How long will a water drop exist until it evaporates based on ambient conditions? [closed]

How long will a water drop exist until it evaporates based on ambient conditions? I am looking for a simple equation or table that would tell me how long a water drop may exist until it evaporates ...
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620 views

Sensible heat question (solving for temperature)

If $55 034.175 \rm{kJ }$ of heat are transferred to $150 \rm{kg}$ of ice at a temperature of $-12.15 ^\circ \rm{C}$, calculate the temperature of the resulting water. Using $Q = mc(t_2-t_1)$ or ...
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469 views

Have negative pressures any physical meaning?

Some cubic thermodynamical equations of state predict negative pressures, have negative pressures any physical meaning? Could they be related to negative mass?
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254 views

Rate of Cooling

I was given the following problem: Two objects have a temperature difference of 20 degrees C at time 0. Two minutes later, they have a temperature difference of 18 degrees. How long does it take ...
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181 views

What pressure or tension occurs in a glass jar when I pour boiling water inside?

Sometimes it happens that when you pour a boiling water into a glass jar, it cracks. Since glass is very hard material and resilient to pressure, the tension must be very high. Is it possible to ...
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113 views

How to solve state parameters using these givens for an ideal gas?

In a thermodynamic turbine using air as an ideal gas, given that you have a known inlet temperature value $T_i$, a known exit pressure value $P_e$, a known inlet and exit velocity $V_i$ and $V_e$, a ...
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1k views

Determine the Dependence of S (Entropy) on V and T

Why can the equation $$dS= \frac{1}{T} dU + \frac{P}{T} dV$$ be expressed as $$dS= \left. \frac{\partial S}{\partial T} \right|_V dT + \left. \frac{\partial S}{\partial V} \right|_T dV \quad?$$
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2k views

How to describe heat transfer between two solid materials?

A general equation for dealing with heat transfer between one material and a region of insulating material. I've seen basic heat transfer equations for one material, but I'd love to see an explanation ...
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1k views

Does an object's color change its rate of cooling?

The motivation for this question comes directly from this thread. The proposition is that the color of something changes how fast it cools (note: specifically the rate of cooling, not taking into ...
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4k views

How can my water cool down more quickly?

I have a cup and I can only pour hot water inside, I wanna know whether the heat will dissipate more quickly with more water or less water? How about the occasion when my cup is well covered?
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2answers
364 views

Most efficient type of heat pump

Can I make a heat pump beat the Carnot efficiency? Why is the Carnot process the most efficient one? If I have a heatpump that is sphere shaped, and cascaded in layers like a onion can I beat Carnot ...
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353 views

A formal procedure for thermodynamic relations

This is my third time taking a thermodynamics course (two in undergrad, one in grad), and I've finally become frustrated enough about something to post on here. A lot of thermodynamic questions want ...
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50 views

Reconciling Units in Jeans' Criterion Formula

In "Physics and Chemistry of the Solar System" Jeans' Criterion is given as: $\frac{GmM}{R_c} = \frac{3mkT}{2}$ ... To me this suggests that on the left we have Joules, and on the right we have ...
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60 views

How hot would a disc have to be to create strong drafts that lift it upward?

I read this article on xkcd.xom, from its spin-off blog "What If?" and that answer made me wonder. It was mentioned in that article that a very hot but indestructible box would eventually be able to ...
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125 views

Is the crystallization of a heat pack the same as the crystallization of freezing water?

Is the crystallization of a heat pack the same as the crystallization of freezing water? If so, why does one generate heat where the other does not?
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127 views

Thermodynamics and electromagnetic fields

The energy density in an electromagnetic field is given by: $u = (1/2) <\vec{E}^2 + \vec{B}^2>$ where $<,>$ denotes the average over time. In a cavity it holds that $u= u(T) = ...
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171 views

How much money does an unused but plugged-in cellphone-charger waste in a year, if its not getting warm?

Is it right as xkcd states: You can use heat flow to come up with simple rule of thumb: If an unused charger isn’t warm to the touch, it’s using less than a penny of electricity a day. Or, more ...
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3answers
597 views

Why the temperature is getting lower when the universe is expanding

As we know, if an ideal gas expands in vacuum, as its energy is unchanged, the temperature remains the same. An ideal gas's energy does not depend on volume. In general, the energy is $kT$ times the ...
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648 views

Is there a formal definition of a macroscopic variable in statistical mechanics?

Intuitively it's easy to accept that the usual variables like temperature, internal energy, etc. are 'macroscopic', but does there exist a formal definition of a macroscopic variable? In other ...
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308 views

A simple thermodynamic question? [closed]

I tried this question a lot of time and few day's earlier I also solved it correctly but I don't know why I am not able to solve it now. I can't get what link I am missing. ques: 2 moles of helium gas ...
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585 views

When should I take wine out of the fridge - transient heat transfer problem

I am hosting a dinner tonight for which I'll be serving white wine (Riesling to be more specific). Generally white wine is best served chilled (not COLD!) at around ...
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1k views

What if the earth's core goes cold?

What effects would occur if the earth's core goes cold? Would the planet stay liveable after this happens?
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8k views

Formulae for Heat Change and Internal Energy Change in a Thermodynamic Process

Today, we were being given a lesson on Thermodynamics when my brain encountered an error. It is easy to derive that, $\Delta U$, the internal energy change for constant volume process is given by, $$ ...
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Energy equation for an open system

I teach undergraduate thermodynamics and I was quite ashamed that I couldn't explain to a student, the following. I thought I'd bring it to physics.SE in hope of providing my student a good ...
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1k views

Can low temperature plasma exist?

Plasma is ionized gas which as far as I know only occurs at high temperatures. When plasma cools down it tends to recombine with the electrons present and turn back into gas. But what if the ...
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140 views

Is it possible to condense heat?

Suppose that I have a warm room. Is it possible to condense the heat of the room into a small object so that the room turns cold and the small object very hot? If it's possible: How? If it's not: ...
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122 views

Will humid air mitigate airborn dust due to neutralization of static electricity?

I have came to understand that humid air will help prevent electrostatic forces that can propel dust and cause it to cling to surfaces. My first question: is this above statement true? If the answer ...
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1answer
89 views

What controls the heating ability of steamers?

Pictured below is a standalone steamer used for foaming and heating milk for milk-based coffee drinks like cappuccinos and lattes. They can be filled with water up to the pressure relief incorporated ...
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2answers
793 views

Why is there a Global Minimum for the Morse Potential?

For Diatomic molecules, the Morse potential describes their potential energy as a function of separation distance between the two particles. My question is, what is the explanation of of the dip ...
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264 views

Unclear how heat interacts with Navier Stokes

I am playing around with an Navier stokes solver and I'm having trouble introducing heat. Am I right in thinking this would be introduced in the ${\bf f}$ term of ${\partial{\bf u}\over\partial t} = ...
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9k views

Rubber band stretched produces heat and when released absorbs heat.. Why?

I always used to wonder why this happens.. when one stretches a rubberband to nearly it snapping point holding it close to your skin - preferably cheek(helps feel the heat), it emits heat. While ...
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2k views

Why doe we not get a shock on induction cooker?

In induction cooking, eddy currents in cook-pot cause heat to be produced. But why do we not get a shock? Also, why is it that current is converted to heat while it has a good conductor(say, steel) ...
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384 views

Thermo homework (HW) problem

I do not believe this question can be solved with the thermodynamics knowledge that I have learned thus far, but someone correct me if I am wrong: A 0.2-m³ tank containing helium at 15 bar and ...
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1answer
162 views

How can dQ/T be interpreted as a system's level of disorder?

Long before statistical mechanics, entropy was introduced as: $dS = \frac{dQ}{T}$ At the time when entropy was introduced in this manner, was it known that entropy represents how "disordered" a ...
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130 views

What happens to the time it takes for my noodles to cook, and the temperature of the boiling water?

I have a boiling pot of water that I am going to cook my Sponge Bob Noodles in. I am very hungry and want the noodles to cook faster, so I turn up the heat from medium to high.( Note, the water was ...
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2k views

Adiabatic expansion of steam through a valve

I'm working on a homework problem, and I have a suspicion the textbook is trying to trick me. The question is: "Steam at 20 bar and 300 C is to be continuously expanded to 1 bar. Compute the ...
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1answer
146 views

Dynamic structure factor

Dynamic structure factor is the spatial and temporal Fourier transform of Van Hoves time dependent pair correlation function. It is written as $$ S(k,\omega)= \frac{1}{2\pi}\int F(k,t)\exp(i\omega ...
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51 views

Height of a piston in a heated cylinder containing H2O

I'm a first time user and I hope I won't be too enigmatic asking the following question: I have a cylinder (radius= $6$ $\text{cm}$) with a frictionless piston on top of it and inside $30$ $g$ of ...
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85 views

Several questions about spring chiller and LMTD

I'm designing a simple copper coil wort chiller. Digging formulas I'm having hard time to figure some things out, perhaps some simple guides may help me to go the right direction: LMTD need inlet ...
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1k views

Historic derivation of Wien's law

Every book I've read, including a lot of websites, Wikipedia, etc, say that Wien derived this: $$\rho_\nu(T)=\rho(\nu,T)=\nu^3f\left(\frac{\nu}{T}\right)$$ Being $\rho_v(T)$ the spectral enegy ...
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3k views

Calculation of number density from material density

Material density is given by $ \rho =m/V$, where $m$ is mass and $V$ is volume. Again number density given by $n=N/V$, where $N$ is the total number of particle. How can I calculate number density $n$ ...
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1answer
397 views

Maxwell-Boltzmann velocity PDF to CDF [closed]

I asked on Math.SE and was advised to try here instead. I need to draw from a Maxwell-Boltzmann velocity distribution to initialise a molecular dynamics simulation. I have the PDF but I'm having ...
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1answer
216 views

What's the underlying particle physics of endothermic reactions?

I don't just mean reactions that require heat to proceed, storing surplus energy in chemical bonds. I wonder about strongly endothermic reactions that suck heat out of environment. You take some ...
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3k views

Plotting the maxwell-Boltzmann velocity distribution in matlab

I'm trying to plot a maxwell-boltzman velocity distribution in matlab. I have also asked this question at cross validated without much luck The PDF is f(v)=sqrt(m/2*pi*k*T) * exp(-m*v^2/2*k*T) ...
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340 views

What would result in a transformer that has its secondary wires disconnected from any circuit?

I am studying magnetism and I am curious as to what happens in a transformer that has its secondary output wires connected through a circuit versus one that doesn't. My main questions (in the case of ...
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298 views

relation between first law of thermodynamics and statistical mechanics definition of entropy

From the definition of entropy as $S= - Tr (\rho\, ln \rho)$ one obtains that $S = \frac{\langle E \rangle}{T} + \log Z.$ The first law of thermodynamics has $dS = {dE \over T}$. Why is there no ...
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158 views

Does the Kelvin have a rigorous definition?

From Wikipedia: The kelvin is defined as the fraction 1⁄273.16 of the thermodynamic temperature of the triple point of water. That presupposes that we can take a fraction of temperature. Now, ...