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

learn more… | top users | synonyms (1)

0
votes
0answers
35 views

Does Expanding Universe conflict with the Thermodynamics 3rd Law?

I know that thermodynamics 3rd law states that if a system in equilibrium is at zero temperature, its entropy is minimum. Expansion of the universe made a transition from radiation dominated era ...
1
vote
2answers
52 views

Entropy - does Heat Death occur in a closed system

Does heat death occur in a closed system? (Assuming you can theoretically have some sort of "closed system".
0
votes
1answer
31 views

Efficiency of a real engine

Can anyone tell me what is wrong with the following argument? Consider a Carnot engine and an engine $X$ whose efficiencies are $\eta_c$ and $\eta_x$ respectively. Let us assume that ...
0
votes
0answers
17 views

An interesting question on the mass of a droplet of liquid experiencing the Leidenfrost Effect

Background and Inspiration: I have seen numerous demonstrations of the leidenfrost effect, both on the internet and in my mother's kitchen. But I started wondering about a general case after having a ...
0
votes
0answers
19 views

Refrigeration Apparatus flow meter location [on hold]

What would be the reasoning for locating the flow meter in it's location in the following refrigeration apparatus (from a thermodynamics perspective):
0
votes
1answer
24 views

in which part heat travels faster

A room has one wall made of concrete, one wall made of copper, and one wall made of steel. All of the walls are the same size and at the same temperature of 20°C. Which wall feels coldest to the ...
3
votes
1answer
33 views

Why is my breath hot when i open my mouth all the way, but cold if I blow like a whistle? [duplicate]

I observed this as when I want to cool my soup I blow like a whistle and when I want to warm my hands I open my mouth more as my breath is warmer now.
0
votes
0answers
32 views

Thermodynamics - Efficiency of an engine [on hold]

I am taking a mathematical physics course and got stuck on this rather simple problem Consider a thermodynamic cycle of monoatomic gas () I want to calculate efficiency of this cycle I know that ...
0
votes
1answer
43 views

Is the gas constant really a constant?

For ideal gases we have $$ C_p-C_v=R $$ now the left hand side of this equation is temperature dependent, so how is it possible that gas constant $R$ is temperature independent?
13
votes
5answers
2k views

Why does my fireplace shoot flames out the front until I open my backdoor?

I have a natural gas fireplace with fake logs in it. I open the flue, turn on the gas for a couple seconds, and throw a match in. The flames kind of go up and out of the flue, but most of the flames ...
0
votes
0answers
24 views

Is using molar terms with maxwells relations misguided?

My professor wants me to do a lot of derivations using maxwells relations. One of the things he wants me to prove is that from the Van der Waals equation of state one can say: $\Big(\frac{\partial ...
1
vote
2answers
51 views

An equation to describe a process of heating one room using hotter air from another room

There are two rooms completly isolated from the outer world (a closed system, no heat losses). They are connected with each other through a ventilation tube. Temperature in room A is 32 degrees ...
0
votes
2answers
47 views

The 1st law of thermodynamics

If a gas expands adiabatically will the work done be positive or negative? I think it will be positive as $\delta W=p dV$ and we have a positive sign due to the work done by the gas is positive as it ...
1
vote
2answers
65 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?
0
votes
2answers
99 views

How can Maxwell's Demon erase information while a black hole can not?

It is stated, that information can't disappear even in black holes. On the other hand, it is stated, that mystic beings, like Maxwell demons, can easily erase any information if they just pay with ...
4
votes
2answers
1k views

Where does information go if thermodynamic death?

Often read that until Hawking the black holes were introducing a problem with information. Allegedly information should be unable disappear, while this was happening in classic black holes. What ...
0
votes
0answers
13 views

Kettle barbecue thermodynamics question

I have an old kettle barbecue which lost its legs to rust. I then placed the dome on top of a truck's brake drum and throttled the airflow by mounting the brake drum on a plate with holes drilled in ...
0
votes
1answer
30 views

When will internal energy change?

If a gas expands irreversibly and adiabatically from $(V_i, p_f+const)$ to $(V_f,p_f)$ will the internal energy change? I have two thoughts: 1) Yes because $\Delta E= \Delta Q + \Delta W$ always ...
2
votes
1answer
55 views

The fly and the sphere of iron

When I was a child, I read something like the following in a book whose name I have now forgotten (I tried to find the original quote on the web, but although there are some similar passages the ...
0
votes
2answers
35 views

What is the cause of the flash of light and debris immediately above this explosion?

First - the footage of the explosion in question: http://www.discovery.com/tv-shows/mythbusters/videos/homemade-diamond-high-speed/ More specifically, about 5 seconds in, I'm speaking of the ...
1
vote
2answers
37 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 ...
-3
votes
0answers
80 views

Does This Video Really Prove that Energy Conservation Can Be Violated? [on hold]

I've discussed the following video elsewhere: http://youtu.be/YBMUzoUJ7ww and am more and more coming to the conclusion that the video shows for the first time scientifically sound proof that ...
0
votes
0answers
22 views

Melting icicles

If I break off the bottom half of an icicle, will the top half melt faster?     ...
14
votes
1answer
2k views

When heat is applied to the top of a stack of pennies, why does the bottom penny melt first?

I just watched this video where a blow torch is used on the top of a stack of pennies. I'd like to know why the bottom penny melted first.
6
votes
2answers
576 views

Is it possible to disprove water memory with an entropy argument?

Water memory was a controversial experiment claiming to provide an explanation supporting homeopathy. The results were largely dismissed as being tainted by experimental error. One possible mechanism ...
1
vote
0answers
30 views

When did the casual definition of the three laws of thermodynamics first appear? [closed]

Who is credited as the source, and when were the laws first stated in this form? (1st Law) You can't win. (2nd Law) You can't break even. (3rd Law) You can't get out of the game.
1
vote
1answer
38 views

Does $\delta W=pdV$ hold for non-ideal gases

I have that for quasistatic processes, $$ \delta W= \textbf{f}\cdot d\textbf{x} $$ so for a gas $\delta W=pdV$. Does this only hold ideal gases or will it hold for van der waal's gas?
0
votes
0answers
31 views

Physics p-v diagram [closed]

Shown below is the P-V diagram of a system where a change from state 1 to 2 is accomplished through three separate paths. Given that p1 = 150000 Pa, p2 = 50000 Pa, V1 = 20 L and V2 = 80 L ,what is the ...
-2
votes
0answers
28 views

Chemistry in real life [closed]

2.5 moles of an atmospheric gas occupying 4 L volume at 278 K contracts to half of its initial volume against a constant pressure of 1.5 atm (1atm = 101300 Pa). Calculate the work in kJ. Make sure you ...
1
vote
2answers
78 views

Finding Maxwell relations

I feel I am missing something about deriving Maxwell relations. I have read http://ocw.mit.edu/courses/physics/8-044-statistical-physics-i-spring-2013/readings-notes-slides/MIT8_044S13_notes.Max.pdf ...
0
votes
1answer
14 views

Cooling effect of sipping

Is the primary action of cooling of a sipped hot fluid explained by the reduced flow of the hot fluid, the air cooling of the fluid as it is sipped or another factor?
0
votes
0answers
14 views

Equation of State of PVT system

Find the Equation of State of a fluid with Volume expansivity $\alpha_P$ and an isothermal compresibility $\kappa_T$ are given by $$\alpha_P=\alpha_0 \Big(1-\frac{P}{P_0}\Big) \\ \: \: \: \: ...
3
votes
2answers
360 views

Temperature of space

What will be temperature inside an isolated box in empty space? By isolated I meant light from stars cannot enter the box and there is no matter inside the box.(no vibrations or movement of molecules ...
0
votes
1answer
59 views

Entropy and the $2^{nd}$ law of thermodynamics

I have just been introduced to the word "entropy" and as it is my understanding that it is a measure of the randomness and chaos of particles in as system. My textbook list the 2nd law of ...
0
votes
0answers
35 views

What is the essence of the renormalization flow? [closed]

Recently I started learning QFT and I am trying to understand the renormalization group (RG), however I have some difficulties. Is the whole concept just based on tracing out certain (irrelevant) ...
0
votes
0answers
11 views

Weight and flow rate [closed]

I have a CO2 gas cylinder of diameter 350 mm and height 1500mm height. the pressure in the cylinder is 28kg/cm^2. If the out let hose opening is 1mm in diameter, (1) What is the weight of the gas ...
0
votes
0answers
18 views

Isothermal Expansion in Real Gases

I understand that for a ideal gas in the case of reversible isothermal expansion, $\Delta U=0$ and $-Q=W$ but in case of a real or van der Waal gases, how can I find $Q$, $\Delta U$ and $\Delta S$?
0
votes
1answer
43 views

What sort of math deals with thermodynamics inside of semiconductors?

That is to say, how would one consider the thermodynamics of a complex chip like a modern CPU? I hear that designing the thermal efficiency of such systems is very difficult. I'm not sure why, ...
0
votes
1answer
34 views

How to thermodynamically understand process of burning a piece of coal?

Let's imagine that I have a match in hand and nugget of coal on my desk. Then I light up the match and place it for few seconds near the coal so a tiny piece of nugget catches fire. Then another piece ...
0
votes
1answer
29 views

Dielectric heating - does EM field transfer energy to polar molecules?

In AC field, polar molecule are trying to align with external field. At high freguencies, changes of field are so quict, that molecules cannot align with it. This leads to increasing kinetic energy of ...
0
votes
1answer
25 views

What assumptions can be made using a $pV$ diagram?

In this question I am asked to find the volume of a gas at $V_3$ I have some parts that am not clear on. Is it reasonable to assume the temperature at $3$ is $657^{\circ}C$ Work is done by the ...
0
votes
1answer
30 views

Heat transfer through radiation and its relation with temperature

My question is: if a body and the surroundings have the exact same temperature, will that body still lose heat in terms of radiation? If so then what exactly is heat. Heat is defined as energy flow ...
2
votes
3answers
170 views

Does placing a cold bottle next to an incubator cool the incubator through convection or radiation?

Context for question: My girlfriend who is studying to be a nurse asked me to explain the difference between radiation and convection in context of the above question. My answer: Radiation is the ...
1
vote
0answers
23 views

Callen Thermodynamics 2.8-2 help? [closed]

A two component gaseous system has a fundamental equation of the form $S=AU^{1/3} V^{1/3} N^{1/3} + \frac{BN_1N_2}{N}$ where $N=N_1+N_2$ and $A$ and $B$ are positive constants. A closed cylinder of ...
1
vote
1answer
57 views

What is thermodynamic equilibrium?

The state of thermodynamic equilibrium is typically defined referring to the system's behaviour in the future. Can the definition be formulated in terms of measurable quantities?
0
votes
1answer
32 views

Pressure, Momentum and Energy: A 'Peculiar' Relation

Is the following possible? $$ P = \frac{p^2}{3E} $$ where $P$ is pressure, $p$ is momentum and $E$ is energy. In what convention is the above relation acceptable? EDIT: The source paper can be found ...
0
votes
2answers
40 views

What is the heat sink in an internal combustion engine?

I believe that the heat source is the spark plug because it heats up the fuel-air mixture and that the working substance is the fuel-gas mixture. Then, I know that the explosion created by the fuel ...
-4
votes
1answer
71 views

Is information a form of energy? [closed]

To better describe my question, do the following experiment: Calculate x=12+26+67+71 Now you might have spent some time in getting the answer. You burnt sugar, you used up energy to get the ...
2
votes
1answer
106 views

How does this new theory of a possible infinitely old universe not violate the second law of thermodynamics

I read the following article: http://phys.org/news/2015-02-big-quantum-equation-universe.html And followed it back to this journal reference : http://arxiv.org/abs/1404.3093 It appears to be ...
1
vote
2answers
109 views

Extensive variables in thermodynamics

Extensive variables in thermodynamics are those which scale linearly with the system size. It is known that a ratio of two extensive variables is an intensive variable. Now, the number of particles ...