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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How could be modelled this heat transfer problem?

I have been puzzled the other day by a young boy who asked me about the phenomenon making that, when arriving to the shower, water is cold. Simple, isn't it? I started describing, in simple words, ...
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77 views

How do you calculate oxygen temperature as atm pressure changes? [closed]

I know that when gases are decompressed the atoms suddenly have a bunch of space and absorb all the heat around them thereby giving the effect that it is cool but how do you calculate this for oxygen ...
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132 views

Compression vs. Friction - what happens when space objects enter earth's atmosphere

When reading about what happens when cosmic debris enters the earth's atmosphere, some sources say friction, others say compression. For example: On space.com it says: Meteor showers occur when ...
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47 views

Does a ceiling fan air heat up the air?

I was laying in bed one day, looking at my ceiling fan, when I wondered, "Doesn't the ceiling fan, because it makes wind, cause wind chill, which 'wicks' heat away from me -> making me feel cooler, ...
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50 views

Ideal gas law with two types of gases

Suppose a container with volume $V$. If I put 2 different types of monoatomic ideal gas, say type $A$ and type $B$, such that there are $N_1$ particles of gas $A$ and $N_2$ particles of gas $B$, with ...
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41 views

Hot Object In a Cooler Space [closed]

How would you calculate the heat given by an object that is hotter than its surroundings? I know there's Newton's Cooling Law, but what about any heat given off by radiation? Are these additive ...
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118 views

Why is it so hard to explain that the Brownian Ratchet doesn't work?

The Brownian Ratchet stood up to a lot of scrutiny before it was finally shown why it would not work as a perpetual motion machine, but it seems weird to me that all of that was necessary. If the ...
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93 views

Discrete time simulation of gas liquid equilibrium in a tank

I am trying to write a discrete time simulation of liquid/gaseous oxygen in a pressurised cryogenic fuel tank. For now I am assuming that the only external change to the system is the influx of heat ...
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60 views

How to calculate max temperature craft needs to withstand near the Sun

The Solar Probe Plus fact-sheet states that the craft will approach to the distance of 9 solar radii to the surface of the Sun (Approx 6.26e6 km) and its heat shields must withstand 1644K of heat. I ...
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58 views

Temperature of system in canonical ensemble

Upon reading Reif's explanations relating to systems exchanging energy and the canonical ensemble (Reif, Fundamentals of statistical and thermal physics, p. 95ff and p. 202ff), I am led to conclude ...
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30 views

Water's Specific Heat Capacity as an Outlier

Can the specific heat capacity of water being ridiculously high as compared to other substances be explained at a molecular scale?
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62 views

How is one process reversible and its reverse non-reversible?

My textbook gives this example of a reversible process: A gas in a piston is expanded over a long period of time, sitting on a hot plate that maintains its temperature. As an infinitesimal amount of ...
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236 views

How much energy would be required to make one tea cup full of Earl Gray tea at 100F?

On the TV show "Star Trek: The Next Generation", Captain Picard is often pictured using a replicator to materialize a cup of "Earl Gray tea, hot". Besides wondering what they do with all the empty ...
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61 views

Heat capacity of solids

In the Einstein/Debye models, the specific heat capacity goes as T^3 at low temperatures and approaches the Dulong-Petit law at higher temperatures. I undestand that some molecular motions (rotation, ...
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206 views

Confusion about heat capacities at constant volume and constant pressure

Let's take water for an example: the specific heat for water vapor is 1.99. This would mean that the molar specific heat is the molar mass times the specific heat (or $18.0*1.99 = 35.8$). Is 35.8 ...
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84 views

Is entropy violated inside black holes and worm holes?

Do the laws of thermodynamics hold true everywhere in universe ? What about black holes and worm holes ?
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68 views

Black body in thermal equilibrium

In the answer of an exam said that a black body in thermal equilibrium with it's surroundings won't emit any energy, but I don't really understand why. My logic is that every object emits ...
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73 views

Formation of bonds and heat release

We know when there's formation of bonds during chemical reaction there's heat release to the surrounding due to conservation of energy. But what I am confused about, is the kinetic energy of the ...
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73 views

How to find the variation in temperature at a certain point inside a body undergoing heat transfer via conduction?

I am trying to find a way with which I can find out the temperature of a certain point inside a body undergoing thermal conduction. I understand that this might not be very simple to calculate since ...
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50 views

Does venus have plasma in its atmosphere?

Is it hot enough on Venus for thermal collisions to ionize molecules? If not, what temperature would it have to be?
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158 views

When i tear a paper, can i accidentally create nuclear fission?

I know it's a stupid question... but when I tear a paper i may coincidentally split it and create nuclear fission. When i tried experimenting, by tearing the paper for HELLKNOWS how many times, I ...
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87 views

Why does a cloud form around ice cream?

Everyone have probably seen the phenomenon as one opens a cool ice cream from its pack, a white cloud begins to flow around the ice cream surface, and it constantly spreads out until the ice cream ...
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2answers
86 views

Entropy reversal in magnets

Entropy is an irreversible phenomenon without any energy supplied to reverse it. I was reading about paramagnetic substances and how dipoles align inside them on application of magnetic field. My ...
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1answer
217 views

Why is Cv used in the adiabatic expansion of Carnot Cycle to calculate internal energy

When I took this class years ago, I simply accepted it as fact. However, now that I'm teaching it, the following bugs me....a lot. Why do they use Cv to describe the change of internal energy during ...
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125 views

If heat can't be transformed into other forms of entropy, why do hot things radiate electromagnetic waves?

The laws of entropy says entropy can only increase. On the other hand, if I take a hot object, it will naturally convert its heat into EM radiation. How is this possible? Does EM radiation count as ...
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1answer
89 views

Reversible cycle approximated by Carnot cycles

My textbook, W.E. Gettys, F.J. Keller, M.J. Skove, Physics 1, gives the definition of a reversible transformation as a transformation that can be inverted by effectuating only infinitesimal changes in ...
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231 views

Paradox of potential energy of gas molecule

We know that when water is heated at its boiling point, it will become vapors. Then because there is no change in temperature, the heat supplied will be transferred to the potential energy of the ...
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88 views

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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104 views

canonical ensemble that is quantum mechanical and continuous?

I do not understand what the following statements from Wikipedia mean For a canonical ensemble that is quantum mechanical and continuous, the canonical partition function is defined as $$ Z = ...
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70 views

Finding the Enthalpy of an Ideal Gas given internal energy

I am trying to find a formula for tying things up. Given an ideal gas like helium or nitrogen gas (diatomic) how can I find its enthalpy simply given internal energy? I remember it was once taught in ...
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137 views

Preventing Heat Escape

Is is possible to completely prevent heat from escaping from a closed container? Here is a diagram of vacuum flask, which tries to implement the design - Vacuum Flask prevents heat from escaping ...
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85 views

Is possible to synthesize diamond at relatively lower pressures (6 to 7 GPa vs 12 GPa)?

Pure binderless nanopolycrystalline diamond can be produced from graphite when the graphite is treated with more than 12 GPa pressure and at least 2100°C temperature . If we treated graphite or ...
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61 views

Tap water in the cold glass

It is fairly long time I was in school and I was particularly bad at thermodynamics. This is an question I was trying to comprehend. I have 500ml of tap water @ 20°C. I pour it into heavy glass ...
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40 views

Deriving the partition function in MaxEnt

I'm trying to understand this paper on Maximum Entropy by Jaynes, and am stuck on something which should be rather simple. We're attempting to maximize the entropy $-\sum_i p_i \ln(p_i)$ subject to ...
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59 views

Shape of metal to be heated in consumer microvave oven? [closed]

I tried to use a common 900 W microwave oven melt some alloy with low melting point (138 deg C, eutectic bismut/tin). The metal did not heat up, neither did the metal container, which makes me think ...
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114 views

Definition of 1 calorie

Why has the definition of 1 calorie been taken to be the energy required to heat 1 gram of water from 14.5 to 15.5 degree centigrade at standard pressure? Is there any specific reason for taking the ...
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81 views

Charles Law inverse for cooling?

Is the inverse of Charles law also true? If I double the volume, the temperature will be halved? In the fire service we ventilate a structure by opening up the ceiling to the attic. If the volume of ...
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3k views

How long does it take for water to boil when subjected to intense heat?

I have a rather odd question that may just boil (sorry) down to a fairly simple problem I can't solve. The scenario is this: A person is testing the intensity of a super-focused beam of sunlight in a ...
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1answer
109 views

Legendre transformation: non-convex/non-convave functions

The Legendre transformation is used to derive the Hamiltonian from the Lagrangian, and it finds many applications in thermodynamics to convert between the different potentials. $ f(x) \rightarrow ...
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110 views

What is the best thermal heatsink compound?

Re-worded This is about the Experimental Physics not PC building or how to grease a car's radiator. I have to insert a stainless steel enclosed PT100 into a block of metal to monitor its temperature ...
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128 views

Partition function: Number of states? Doesn't add up for ising

While trying to really understanding the partition function in statistical mechanics, I tried looking at it for a 2D ising model, as that's been helpful for me for all kinds of thermodynamic values. ...
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99 views

Are black holes hot?

If no light can escape black holes, in my mind they would act as a greenhouse, collecting radiation from the stars or CMB or anything. Or is all this energy just absorbed by the black hole?
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101 views

Can an object appropriately isolated from its surroundings become colder than its surroundings?

Consider a sealed box, well-insulated on all sides, except for the lid which is transparent to infrared. An object is placed inside the box and the box is evacuated (purpose being to thermally isolate ...
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233 views

Entropy and Gibbs Free Energy

I've been struggling with the notion of entropy and gibbs free energy for almost three days now. Different sources on and off the internet say different things about entropy. Gibbs Free Energy is ...
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89 views

Proof of the Boltzmann factor

The following derivation of the Boltzmann factor is obviously wrong, or incomplete: $$p(E) \propto \Omega(U-E)$$ Consider the Taylor expansion of $\ln\Omega(x)$: $$\ln\Omega(U-E)\approx \ln ...
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240 views

Relation between work and internal energy in an Isothermal expansion

I don't understand why the change in internal energy in an isothermal expansion is considered to be 0. In an isothermal process is done work, so, shouldn't that imply that the internal energy changed? ...
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161 views

What material can achieve the highest temperature before failing when being heated by electricity?

Just as a qualifier, I barely made it through physical science in college, so... Please be detailed in your answers and assume I know nothing. Let's say I wanted to make an electrical coil for the ...
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1answer
144 views

Why doesn't oxyhydrogen flame travel through a narrow pipe?

In this video someone filled a syringe with oxyhydrogen (2:1 hydrogen-oxygen mixture obtained with a "brown gas generator", an efficient electrolyzer). The mixture at the tip of the needle was lit ...
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1answer
218 views

Boiling water at low pressure with heat supply

I understand that water boils at lower temperatures at lower pressures, but I want to know what happens when external heat is supplied to a body of water at low pressure. Suppose I have a hot object ...
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97 views

How to make the mixed water warmer?

Freezing cold. Nastily I still have to do the laundry by hand. And to keep my hands from being frozen I have to add some hot water to the freezing tap water. Let's just suppose that I have the same ...