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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3answers
56 views

The temperature a liquid would boil: question incorrectly formulated or not?

I have met a question in a high school physics book which I think is incorrectly formulated. The question is this: In order to reach boiling temperature, a certain liquid requires twice the amount of ...
0
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1answer
27 views

Functions of state and definition of equilibrium

Consider this - A function of state is any physical quantity that has a well-defined value for each equilibrium state of the system. (Blundell and Blundell - Thermal Physics) My question is - Are ...
1
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0answers
36 views

Self-powered heat exchanger w/energy profit? [closed]

It is possible, considering the laws of physics, to build a heat exchanger that runs on the power it gathers from the environment? A typical heat exchanger uses less power to harvest heat for a ...
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2answers
83 views

Heat diffusion in a house

I was wondering about this problem (which is NOT homework, it's one of my mental problems due to what surrounds me): supposing I'm in a room, and it's winter. Heating is on, the boiler works and the ...
0
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2answers
68 views

Heat rejected by a refrigerator?

What is the amount of heat rejected by the condenser of a vapour compression refrigeration system, typically those found in households? Something in the nature of a 25W compressor, for example
3
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0answers
93 views

My bathroom door stays open in summer [closed]

My bathroom door remains open in summer, but in the winter it stays about halfway between fully open (90 degree angle, against a window) and closed. The door is between bedroom and bathroom and it is ...
-1
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1answer
50 views

Kindling to make a fire

I know that rubbing stuff like dry grass or wood on firewood works to make a fire but why does it work? I think it is because the friction produces heat but then how come our hands don't get on fire ...
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0answers
10 views

Do we know how much energy is released in internal conversion (fluorescence)?

In the Jablonski Diagram, when photons hit a surface and certain frequencies are absorbed, then internal conversion occurs to the excited portions of the surface and energy is released as heat (If I ...
5
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1answer
111 views

In a Monte Carlo NVT simulation How do I determine equilibration

I'm running an NVT (constant number of particles, volume and temperature) Monte Carlo simulation (Metropolis algorithm) of particles in two dimensions interacting via Lennard-Jonse potential ($U = ...
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8answers
4k views

Entropy is…disorder?

As I read somewhere, it said that the universe is heading toward disorder a.k.a entropy increasing. Now as far as I know from the second law of thermodynamics it states that entropy is indeed ...
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0answers
26 views

Cooling of a surface due to fluid passing over it

I am working on a project that requires me to measure the cooling effect of a liquid flowing through a surface. In order for me to effectively calculate the cooling effect, the solution of the below ...
4
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1answer
34 views

Is single tree shadow locally affecting air temperature?

In other words, is the air temperature under a single tree different from a couple meters away, in a hot day and under the sun? There are several effects potentially interacting: Tree transpiration ...
0
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1answer
17 views

When does heat conduction become convection?

Okay, I have a hard time wrapping my head around something, I think, pretty basic. For a little hobby project of mine I was making a fermentation-box for beer brewing allowing me to accurately ...
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4answers
71 views

Does change in internal energy $\Delta U =0$ implies that the process is always isothermal?

Does change in internal energy $\Delta U =0$ implies that the process is always isothermal while considering a ideal or real gas ? If not, then what are the other process where $\Delta U =0$ and ...
2
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0answers
35 views

Does entropy flatten spacetime?

Forgive me if this is a non-question, but I could not find anything regarding this. I only know parts of GR, and I am not familiar with the math. Since energy and matter density curve spacetime, ...
0
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0answers
17 views

Material preventing nucleation, why is it not used for soda container?

I would like to know the answer to the question "why do materials preventing heterogeneous nucleation of $CO_2$ aren't used for soda bottles and glasses?". Two possible answers so far that I thought ...
6
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2answers
136 views

Why does warm water sink?

It is well known that water at 4C is denser than water at 0C. This is the usual explanation for why a body of water freezes from the surface (also it's because ice is even less dense, but that's ...
2
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0answers
8 views

Conduction shape factors - textbooks inconsistent

I'm working through a energy flow problem, and need to use the conduction shape factor for 'Row of N long cylinders against planar surface'. However two different texts give two different formulas for ...
3
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0answers
33 views

How much oxygen is required to maintain a constant temperature (400 C) in a BBQ Smoker? [closed]

I would like to calculate the amount of oxygen required to maintain a constant temperature of 400 degrees Celsius inside the firebox (oak wood) of a BBQ Smoker. I found a similar calculation for the ...
1
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1answer
32 views

Carnot cycle and entropy

From what I understand, in the Carnot cycle summing qi/Ti for each step results in zero, thus indicating a new state function, entropy = qrev/T. But since dE = 0 = q+w, then q = -w, and looking at the ...
0
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2answers
57 views

Thermodynamics and Newton's second law

Is it correct to say, that the Newton's laws (or a Newtonian system) is reversible if the friction isn't considered (the fact that the time is of second order $\frac{d^2x}{dt^2}$) and an isolated ...
0
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0answers
26 views

How heat can be transferred away to cool down objects

Based on the 4 ways to transfer heat which is vaporazation, contact, radiation, and convection. If I needed to cool down an object for example a hot soup how would I do it, put it in the freezer to ...
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2answers
91 views

Why can't the entropy of an isolated system decrease? [duplicate]

I read that heat cannot flow from cooler body to hotter because for that entropy of the system becomes negative. Why is that so? Why we cannot have negative entropy?
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4answers
54 views

>50% Heat Engine + Heat pump [closed]

I know entropy rules force my statement to be FALSE. But anyway I haven't been able to find the problem in the statement. Suppose: We have a perfectly isolated cold reservoir at $T_c = 100 K$ We ...
1
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2answers
36 views

Can outgassing produce a significant thrust on a space ship?

There are a variety of materials that outgas in the atmosphere, and I imagine they would do so even more in the vacuum of space. I imagine an object in space would experience a small force as ...
0
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2answers
30 views

Wall vents in house and heat loss

I live in northern midwest of USA--have propane central heat. Electricity is cheaper here than propane sometimes. To aid in heating front room I have 2 electrical space heater--one with fan,and one ...
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1answer
50 views

If two gasses are in thermal equilbrium, do their molecules have same amount of Kinetic energy?

If two gasses are in thermal equilbrium, do their molecules have same amount of Kinetic energy?
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1answer
34 views

How much difference to interior temperature would a white car roof make? [closed]

My van has a mostly dark green exterior which becomes extremely hot to the touch by the middle of the day. Inside the only thing that keeps it bearable is having air con at full and as soon as the ...
0
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1answer
23 views

Thermodynamic / Thermal Property

What is the definition for (i) Thermodynamic Property & (ii) Thermal Property? What are the subtle distinctions in the Thermodynamic Properties and Thermal Properties? ...
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0answers
91 views

Doesn't this LED created by MIT violate the second law of thermodynamics?

Here is the article I am referring to: http://www.wired.co.uk/news/archive/2012-03/09/230-percent-efficient-leds In their own words (or at least the article writer's), "it appears to draw in heat ...
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2answers
43 views

Reversible expansion paradox

consider a mole of an ideal gas enclosed in a container with a mass-less piston undergoing isothermal reversible expansion. now we know that in an reversible process the system and the environment ...
0
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1answer
17 views

Enthalpy of condensation

suppose we have one mole of an ideal gas undergoing a phase change at constant temperature. we know that enthalpy change is given by the formula $n*Cp*\delta(T)$. since there is no temperature change ...
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2answers
50 views

What temperature is an evaporating cup of water at “room temperature”?

If I put 100 g of water in a cylindrical cup and I know it takes 2 weeks (lets say 1.2 × 106 seconds) at some RH/temp to completely evaporate in my room with a constant temperature, can I ...
0
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3answers
81 views

Why is the speed of sound lower at higher altitudes?

At sea level the speed of sound is 760mph, but at altitudes like the Concorde would fly at (55,000ft) the sound barrier is at 660mph, so 1000th slower. Does it have to do with lower pressure?
0
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1answer
30 views

Does the velocity of steam affect the transfer of heat?

I am analysing a heat exchanger system which uses steam travelling through a finned tube to warm air. I am currently looking at reducing time lags in the system so as to raise the temperature of the ...
8
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2answers
624 views

Why things get dry (meaning from water)? [duplicate]

When I leave wet clothes in the open air, they will get dry over time by themselves even at room temperature. I know that somehow the water becomes vaporized; it's not "disappearing". For that, it ...
0
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1answer
21 views

Heat capacity across a phase transition-inconsistency?

In the books I have seen two descriptions of what the heat capacity does across a first-order phase transition. The diagram in this question First Order Phase Transition - Heat Capacity seems to ...
0
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1answer
12 views

Thermal diffusion equation with heat per unit length?

Let us say we have a metal rod. Along that rod there is a rate of heat generation of H per unit length. If we assume we are in the steady state then I would expect us (from the thermal diffusion ...
0
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1answer
51 views

How does compressibility depend on pressure?

I want to calculate the density distribution inside a column of a solid material of which I know all properties (density, compressibility) at the top (room pressure). Using the definition of ...
6
votes
1answer
272 views

How is the perceived quality of sound measured and analyzed?

I am doing a physics experiment researching the effect of temperature inside the clarinet pipe on the quality of its sound. I know that the speed of sound is directly proportional to temperature of ...
3
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1answer
25 views

How to relate heat build up in an open pipe to sound frequency and specific heat capacity of the pipe's material.

I am designing a physics experiment with my clarinet. A temperature probe and a microphone graph changes in temperature and sound pressure, respectively. I am trying to demonstrate how different woods ...
2
votes
1answer
34 views

Calorimetry Problem

I was doing a problem in thermodynamics where the net heat is 0. I dont understand why if you have say a copper calorimeter with water at say, 15C and add a mass of copper at a higher temperature say, ...
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0answers
64 views

Mathematical definition of reversible processes

If I label an initial thermodynamic state as $\psi$ and the final thermodynamic state as $\xi$ then can I say that under a reversible process the two states are related to each other by a continuous ...
5
votes
1answer
211 views

How far away from the Sun does space start to be cold?

I assume that if I stood on the sun, I would be hot. I similarly assume that if I stood about 10 feet from the sun, I would still be hot. However, if I stood in space 93 million miles away, I would be ...
2
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1answer
34 views

Translated publications of Boltzmann

I have been looking for Boltzmann's papers (in english) and had no luck. Anyone knows if they were translated at the first place, and if yes where to find them?
0
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1answer
21 views

Heating and Retaining of Heat in Air

If you have two samples of air then add additional carbon dioxide to one of them and heat them up. Does the one with extra carbon dioxide increase in temperature faster? Does the sample with extra ...
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2answers
48 views

Does extra carbon in air help ice melt faster? [closed]

If you increased the carbon (perhaps more specifically carbon dioxide), in a controlled environment around ice, does it increase the rate that the ice melted?
1
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1answer
31 views

How does conduction happen?

I'd like to ask you how does conduction happen ? I mean, the atoms vibrating more hits the less vibrating atoms and gives energy. But how is that energy transferred ? For atoms to collide they must be ...
1
vote
1answer
35 views

Water + RF + Spark = Continuous Fire

Can anyone explain the physics of what is happening in the following video? https://youtu.be/p8xYUDiSGDk?t=37 Is this process Radiolysis? At what radio frequency & power level is h20 ...
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0answers
30 views

What kind of conservation law is energy conservation in thermodynamics?

As I understand it, Noether's theorem is an important result that allows us to show when certain kinds of conservations arise. Is energy conservation in thermodynamics a result of Noether's theorem? ...