# Questions tagged [thermodynamics]

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

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### Suction cup on car dashboard

I have this suction cup to hold dashcam in car. When I leave car in sun suction fails and camera falls down. Did camera fall because air got heated under suction and expanded or plastic/rubber ...
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### Energy-conservation for exothermic reactions

How do exothermic reactions not violate energy conservation if e.g reactants were given 2200kJ/mol of energy and product released 2300kJ/mol of energy, where has this +100kJ/mol come from?(2200kJ/mol ...
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### How can plasma torches reach 28,000 degrees Celsius?

According to this the plasma of a plasma torch can reach up to 28,000 degrees Centigrade. How is it possible for the plasma to reach a temperature much higher than that of The Sun's surface and not ...
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### Estimate volume of $\rm CO_2$ emission based on compression ratio assuming Otto cycle

The question is: Considering the Otto Cycle, estimate the volume reduction in CO2 emissions per car with an increase in the engine's compression ratio from 10 to 11? Assume one cubic meter of fuel is ...
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### Physical relation between adiabatic constant $\gamma$ and polytropic index $n$

I am study about stellar model of stars by using polytropic equation of state $$P=k\rho ^{\gamma}$$ or $$P=k\rho ^{1+1/n }.$$ I studied that different values of polytropic index $n$ describes ...
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### Validity of Maxwell relation [closed]

I am confused how to proceed with this question. Any help would be greatly appreciated.
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### Temperature Gained in Sealed Tent

Here is the problem I am working on: "Consider a perfectly sealed polygonal tent with the sun directly overhead. The solar irradiance of a surface 90° to the sun’s rays is 1,000 W/m2. However, ...
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### Is the universe a thermodynamically isolated system?

Heat death of the universe can be understood as attainment of thermodynamic equilibrium. But the concept of thermodynamic equilibrium is only valid for isolated systems. What evidence do we have which ...
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### Heating cup in microwave?

I heated my milk cup in the microwave today and noticed that the cup was hot but not the handle. Even if I heat it too much , cups handle temperature remains the same. How is that possible?
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### Does the second law of thermodynamics imply that renewable energy also leads to Global warming/climate change?

So I have this (possibly dumb) question about the implications of the 2nd law of Thermodynamics to the use of Renewable energy for the world, so please bear with me. Here goes: Apart from the ...
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### How does information loss creep into the Bogoliubov-coefficient calculation of Hawking radiation?

I understand the basic idea behind the 1975 Hawking's paper; in the last section there are some comments on the final product of total evaporation. But there is no mention of information loss. I know ...
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### Specific heat calculations - How to input the value of the mass when water is flowing through a pipe?

I have been using this specific heat calculator to calculate the energy in joules needed to cause a change in temperature in a mass of water https://www.omnicalculator.com/physics/specific-heat The ...
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### Can we apply Stefan's law to find how much energy a body absorbs?

Stefan's law tells gives an expression for thermal radiation emitted per unit time by a body of surface area A and temperature $T$ $$u = \sigma A e T^4$$ In my book, it is written that in thermal ...
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### Why do atoms oscillate at absolute zero? [duplicate]

I have heard that average kinetic energy of atoms is directly proportional to the absolute temperature. Then why don't atoms come to a stop at absolute zero ($T=0K$).
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### Second law of thermodynamics about refrigerator [closed]

`Suppose there exists a refrigerator that lowers the temperature of one kilogram of the ocean water by one degree. If the temperature difference between the two sources is 1$^\circ$C. Is it possible ...
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### Can you reach higher efficiencies of the Otto cycle by changing the sequence slightly?

If we take the common Otto cycle we have two isochoric and two adiabatic processes, plus exhaust & intake stroke. Would it be more efficient to do the following: Instead of cutting off the ...
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### What happens physically in a second-order liquid-gas phase transition?

I know the difference between first and second order phase transition in terms of the discontinuity of the derivatives of free energy. I am curious to know what happens as the system is viewed. ...
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### How to obtain hydrodynamics from many-body quantum mechanics?

It is known that the Schrodinger equation is equivalent to the Euler equation (with a "quantum potential" term) and to the probability conservation equation (which is formally identical to ...
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### Are state variables defined outside equilibrium?

State functions seem to always be described as relating state variables in equilibrium, wikipedia about state functions: In thermodynamics, a state function, [...] is a function defined for a system ...
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### Moving boundary work

Moving boundary work can be equated from $\Delta W = p dV$. So can we say that W is a function of V and p is the first derivative of W, f'(v)?
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### Mass lossage of a human over iterative falling due to heat

I watching a video that mentioned that a meteor loses mass as it falls via energy being converted to heat, so say we are on the Burj Khalif ($828$ meters), how many times would a human, say $6$ ft ...
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### Determining entropy of vaporization

In the following van der Waals formula , would shifting the ideal-gas entropy on the left-hand side create an entropy of vaporization equation? In other words, does the real-gas entropy minus the ...
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### How does the temperature and humidity of air affect the water consumption of a humidifier?

We can model the water consumption $\dot{m}_{w}$ of a simple humidifier using the following equations: \begin{align} \eta_{hum} & = {T_{db,i} - T_{db,o} \over T_{db,i} - T_{wb,i}} \\ h_{o} & = ...
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### Energy budget in a buoyant flow

A cavity, subject to gravity, is filled with a fluid initially at uniform temperature. Initially all boundaries are adiabatic surfaces; at time $t=0$ two opposite boundaries (shown in red and blue) ...
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### Applying the fluid pressure equation on gases

The pressure exerted by a fluid at depth is given by: $$P = \rho g h$$ The state variables in an ideal gas are related by: $$PV = nRT$$ For the second equation, we assume the system is in ...
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### Why are iron and copper used more than other materials to make cooking pots?

Why are iron and copper used more than other materials to make cooking pots?
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### Is liquified gas rate of vaporization dependent on the volume of the container?

I have a vessel 50% full of ammonia at outdoor temperature of 20F - 100F depending on time of year. This vessel will be evacuated with a compressor and the vapor will be discharged into an ammonia ...
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### Describing spacetime with qubits

Susskind in one of his lectures at PiTP 2018 on Complexity and Gravity talks about describing black holes as a qubit system, comprising qubits of the order of the entropy of the black hole. This is ...
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### Doesn't this experiment signify that inertial frames are not equivalent? [duplicate]

While reading about kinetic energy something poked in my mind. When we talk about kinetic energy of a body, it is actually the combined kinetic energies of all the atoms in that body. Now suppose a ...
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### What is the relation between the temperature and the radius for an expanding cylindrical thermal shock wave?

I'm reading a paper written by De Rujula and Glashow called "Nuclearites: a novel form of cosmic radiation". In this paper the authors propose the existence of nuggets of strange quark ...
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### Quasiconcavity of the Variance of the Gibbs Measure

Pardon me for taking some time to set up my notation as I do not come from a physics background and am not using the standard statistical mechanics notation. Consider a Gibbs measure on a set of ...
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### Question related to Ideal Gas Law [closed]

A cylinder contains an initial volume $V_1 = 1$ m${}^3$ of a perfect gas at initial pressure $p_1 = 1$ bar, confined by a piston that is held in place by a spring. The gas is heated until its volume ...
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### Can we measure $\Delta G$ when a reaction hasn't reach equilibrium?

Suppose we have the reaction $$\mathrm{A + B \leftrightharpoons C}$$ The system starts with reactants (or products) and reaches equilibrium. Can we measure the change in Gibbs energy $ΔG$ at a ...
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### Does the value of specific heat capacity of a material differ at different surrounding temperature?

I was looking for the exact theoretical value for specific heat capacity of copper. I found some telling 377, 385, 386, 390 J/kgK ... And for different room temperatures, 20 and 25 degree celsius, it ...