# Tagged Questions

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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### Humidity and ignition correlation

Does the same combustible material catch fire more readily at 50*F/100%RH or 70*F/60%RH?
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### Do rotational degrees of freedom contribute to temperature?

Recently I have come across a mathematical problem where I was said to calculate the temperature increase of certain mol of N2 gas confined in a room. However, I found that there was only ...
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### Is a convergent-divergent nozzle a perpetual motion machine of the second kind?

As answered in this question, a convergent-divergent nozzle (de Laval nozzle) accelerates a gas flow by converting its heat energy into kinetic energy. My intuition says that this violates the second ...
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### Would a solid door handle get hotter than a hollow one if there is a fire behind the door?

I am a designer (mechanical engineer) who works for a fire company. My boss asked me to develop and build a new door handle and lock mechanism. Which I did successfully. It has a 16mm Solid vertical ...
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### What happens to the observed thermal energy of objects at relativistic speeds?

When an object is observed to move near the speed of light, what difference in thermal energy is observed? Does time dilation imply that it's colder?
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### Is it true that all processes where entropy increases are permitted by the second law, if the system is isolated?

It is possible to deduce that in a thermodynamic process for an isolated system $\mathrm{d}S$ has to be greater than zero, from this it follows trivially that $\Delta S > 0$. It is usually said ...
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### Calculate pressure from partition function with separated volume geometric parameters?

How does one calculate the pressure from the partition function if it is specified in terms of three parameters defining the space of which the gas occupies, but all three parameters are not always ...
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### What is the relation between entropy and pressure in strict thermodynamic terms?

I read on the net that it is a general consensus that entropy in a system decreases as pressure increases and vice versa. How can one reach such conclusion using the characteristic equation in terms ...
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### Why can't liquid nitrogen be sealed in gas cylinders?

By observing the phase diagram of nitrogen, hydrogen and carbon dioxide, I discovered the supercritical region. I can easily buy a gas tank of carbon dioxide at 250 Bars. However I never saw any ...
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### Why can only asymptotically flat and AdS black hole have the thermodynamics? What's about asymptoticaly dS black hole?

Almost all advanced GR textbooks will have the content of black hole thermodynamics for asymptotically flat black hole. And this paper solve the asymptotically AdS (Anti-de Sitter) black hole http://...
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### Boiling water function

i want to make a program that realistically boils water with all the variables but know near nothing about the math i got the energy transfer equation down but this seems to be giving me some ...
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### Is average kinetic energy equal to the total thermal energy of a gas?

"Average KE" as in this equation: $$K_{average} = \frac{3}{2} kT$$ Since potential energy in ideal gas model is eliminated, I guess this equation is also for the total thermal energy of a gas/a ...
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### Does wax go through a sharp phase transition when it melts?

When ice melts, the system goes sharply from being solid to being liquid. There is no intermediate state where it is soft. This is a true phase transition. The thermodynamic potential is not an ...
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### How is Work by a System Interpretated in the First Law?

Good evening. I've happened to be sitting down today and just couldn't wrap my head around this question which seems rather simple at first. From reading about the first law and sign conventions as it ...
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### Zeroth law of thermodynamics and related discrepancy?

Consider the case: Assume molecules to sphere and their |velocity| as an indication of their temperature. Now for head on elastic collision (i.e transfer of heat), assume the momentum is conserved ...
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### What allows some objects to have a high specific heat capacity?

I know that temperature is a measure of thermal energy associated with the KE of molecules. But when heat enters an object, surely those molecules now start vibrating and translating, so this results ...
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### Efficiency of a compressed air engine

I am doing some personal research on the efficiency of compressed air cars. I am currently trying to come up with an 'ideal' cycle to use as a reference for efficiency (c.f. Otto Cycle for petrol cars)...
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### Accounting for the thermal excitation in the Richardson-Dushmann equation or the work function equation

When accounting for thermal excitation in a system that is not in thermal equilibrium, heat is constantly flowing through a material, should I account for the thermal excitation in the work function ...
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### Is there a formula/relationship between $q$, $m$, $c$, $\Delta T$ and $t$ (time)?

I am currently doing an experiment where I am burning methanol to test for the heat of combustion. To test this, I am heating 100g of water and raising it by 20 degrees Celsius before extinguishing ...
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### What causes a eutectic point?

What causes the melting point depression known as a eutectic point? The temperature depression of a eutectic point can be calculated from the enthaplies and entropies of fusion of the two substances....
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### What is the perfect Ice Cube? [closed]

I have a freezer with -25°C temperature and Soda with +30°C. What is the ice-cube-sized material I can put in the freezer that can bring my glas of soda to the lowest temperature? Are e.g. saltwater ...
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### Expression of heat by the Brownian motion

folks. I was reading a paper from PRE and I'm not sure what's going on about the following equation. So for the system composed of two heat baths governed by Brownian motion, the entropy change of the ...
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### Does an ice cube change its core temperature as it melts?

Let's say we have an ice water solution in an ambience with room temperature, i.e. there is a permanent exchange of energy. Let's suppose the ice cubes were from the freezer, which is at $-18°C$. The ...
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### Alka Seltzer Model: formulas/models requested [closed]

This evening I became fascinated with how my Alka Seltzer tablet disintegrates over time within a small portion of Diet Lipton Citrus Ice Tea. I used a nearly frozen cup; tall, as one might request in ...
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### What happens to the kinetic energy of a dropped ball when it comes to rest on the ground?

If we want to drop a ball from a height, we calculated that potential energy at bottom is zero and we say it is converted into kinetic energy. At that movement, if it is a kind of sand, we find it ...
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### Why do particles in a medium have different speeds?

If thermal conduction occurs because of particles colliding with each other and imparting kinetic energy to each other, won’t the particles of an isolated medium collide with each other until the ...
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### Is there anything that can be heated with least electricity? [closed]

Do you know any element or product that can attain around 400 Celsius of temperature with the least requirement of electricity. I've been looking at the heating coils but most of them are rated as ...
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### Can a Dyson Sphere around a Black Hole be built so that it would not radiate significant IR?

This is related to this question If the sphere surrounded a BH and used it as a heat dump (as well as extracting energy from it by dropping in mass) could its exterior be engineered to match the ...
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### How long will pressure exist in this case?

I'm currently fabricating my project, which currently exists only on paper, and there's one question to which I have stumbled today. Suppose, that I have a pressure vessel capable of holding upto ...
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### Do chemical bonds have mass?

When an exothermic reaction occurs, the energy in the chemical bonds of the reactants is partially transferred to the chemical bonds of the products. The remaining energy is released as heat. For ...
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### Understanding speed distributions: Average speed, RMS speed from a graph?

So taking a look at this graph.... ![http://i.imgur.com/XUwpnSK.png][1] I want to express $A$ in terms of $N$ (total # of particles) and $V_0$. So I've found the piecewise function for $f(v)$ and ...
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### How does fluid velocity affect the dissolution of some solute in the fluid?

Suppose we have a perfect sphere of some solute such as sugar and we place it in a fluid such as water, at a certain temperature, that is not moving. It will dissolve and diffuse into the water due to ...
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### Why is there a pressure drop across a Kaplan turbine?

The Kaplan turbine is an inward flow reaction turbine, which means that the working fluid changes its static pressure as it moves through the turbine and gives up energy. But how does this pressure ...
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### How is it possible that it can get hotter in the car than it is outside?

The Law of Thermodynamics says that two bodies will eventually have equal temperatures. How is it possible that when you leave your car in the sun, it gets hotter in the car than it is outside? Why ...
If I were to have a decrease in temperature with height, $T = f(z)$, I was wondering if I could calculate the pressure like so: Could I simply combine $$\frac{dP}{dz} = -\rho g,$$ with the ideal ...