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 does a canvas water bag cool water?

I was reading about this water bottle by Botl that behaves like a canvas water bags to keep water cool. I found out that this idea is an old idea and cars would drive with water bags in front as shown ...
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1answer
206 views

Any open areas to work in non equilibrium thermodynamics for a Phd student? [closed]

I see that many papers written on fundamentals of thermodynamics(theory) nowadays are by some old professors somewhere(there may be exceptions). Most active young faculty don't seem to be seriously ...
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4answers
582 views

Definition of the entropy

In physics, the word entropy has important physical implications as the amount of "disorder" of a system. In mathematics, a more abstract definition is used. The (Shannon) entropy of a variable $X$ is ...
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1answer
658 views

What meaning does the slope of the efficiency path on a Mollier diagram have in terms of temperature?

Let's say I have a steam turbine that I have modified to increase its isentropic efficiency. As a specific case, consider the modification outlined in the Mollier diagram below. The arrows represent ...
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2answers
723 views

Why do moving particles emit thermal radiation?

While answering another question about heat in an atom, the discussion in the comments led to the question of how heat is related to thermal radiation picked up by infrared cameras. The answer is that ...
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6k views

How does an earthen pot keep water cool?

I understand that evaporative cooling takes place thanks to small pores contained in the pot and that allow some water to go through and evaporate. However I couldn't understand clearly whether water ...
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2answers
233 views

relativistic spaceship, CMB radiation and thermodynamics

Scenario: a spaceship is travelling at a high fraction of $c$. The interstellar gas and CMB radiation has blueshifted significantly and we are facing a possible melting of the front radiation shield! ...
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2answers
317 views

How much energy from extreme coldness?

Let's say I have: 1: one mole of extremely cold ideal gas 2: unlimited amount of ideal gas at temperature 300 K 3: one ideal heat engine Can I generate for example 1 MWh of mechanical energy using ...
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3answers
325 views

Is thermodynamic reversibility a function of path?

Question: given a path taken by a system through state space, is it possible to make a statement such as 'that path corresponds to an irreversible process' or 'that path corresponds to a reversible ...
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2answers
831 views

Gibbs Paradox - why should the change in entropy be zero?

The Gibbs paradox deals with the fact that for an ideal gas with $N$ molecules in a volume $V$ seperated by a diaphragm into two subvolumes $V_1,V_2$ with $N_1,N_2$ particles in each subvolume, ...
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1answer
268 views

Is a black hole's surface area invariant for distant intertial observers?

Let's imagine I'm very far from any massive objects, so my local space-time is Minkowskian. Off in the distance is a black hole, far enough away that it doesn't noticeably curve space-time near me, ...
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3answers
3k views

Given constant T, why does P affect internal energy?

It has always bugged me that tables for water (and other) properties have the capability to look up internal energy as a function of both temperature and pressure. If we limit the discussion to ...
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7k views

Why does hot oil explode when pouring water on it?

I am puzzled to know, What is the reason of hot oil make sound and explode when we pouring water on it?
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2answers
685 views

What happens if you connect a hot resistor to a cold resistor?

Kind of an extension to this question: If you heat up an object, and put it in contact with a colder object, in an ideal insulated box, the heat from one will transfer to the other through thermal ...
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2answers
158 views

Difference between irreversible and entropy?

Cedric Villani recently wrote an article on Landau damping, where at least one topic discussed confused me. Besides discussing the issue of how a process can be microscopically reversible and ...
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3answers
4k views

How air humidity affects how much time is needed for heating the air?

In cold weathers it is suggested to put a humidifier since the air gets too dry. I wonder how the humidity affects how much time is needed to get the air at a temperature of 20 Celsius degrees? I mean ...
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2answers
1k views

Why does the law of increasing entropy, a law arising from statistics of many particles, underpin modern physics?

As far as I interpret it, the law of ever increasing entropy states that "a system will always move towards the most disordered state, never in the other direction". Now, I understand why it would ...
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0answers
1k views

Inflating a balloon (expansion resistance)

I am doing a quick calculation on how to calculate the pressure needed to inflate a perfectly spherical balloon to a certain volume, however I have difficulties with the fact that the balloon (rubber) ...
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3answers
398 views

What is happening as our Universe is expanding? Is entropy increasing or decreasing?

Scientists say that entropy of our universe is increasing as it is expanding and our universe is cooling down gradually from the time of it's birth.If something is getting cooler and cooler then how ...
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2answers
1k views

Connection between entropy and energy

An isolated system $A$ has entropy $S_a>0$. Next, the isolation of $A$ is temporarily violated, and it has entropy reduced $$S_b ~=~ S_a - S,\space\space\space S\leq S_a.$$ Is it true to say: the ...
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2answers
454 views

Intuition behind the concept of heat

Even if elementary, I'm afraid I am still not comfortable with the concept of heat. I can picture heat as some kind of incompressible fluid that is transferred from a body to another in such a way ...
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1answer
1k views

What is heat and how does it effect an atom?

What happens in the atom when it gets heated or cooled and turns into gas, liquid or solid? I just want to know how does heat affect an atom.
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1answer
964 views

Does an object's color change its rate of cooling?

The motivation for this question comes directly from this thread. The proposition is that the color of something changes how fast it cools (note: specifically the rate of cooling, not taking into ...
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1answer
442 views

Why there is no negative temperature [duplicate]

Possible Duplicate: Prove that negative absolute temperatures are actually hotter than positive absolute temperatures Proof of existence of lowest temperature $0 K$ On the Kelvin ...
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1answer
1k views

Heat of vaporization of water - dependence on relative humidity?

Does the heat of vaporization of water depend strongly on the relative humidity of the gas into which it evaporates? Some context: If we want to calculate the dew point of water, we find the ...
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2answers
1k views

Are information conservation and energy conservation related?

as evident from the title, are both, conservation of energy and conservation of information two sides of the same coin?? Is there something more to the hypothesis of hawking's radiation other than ...
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0answers
1k views

What are typical values of the critical thickness of insulation?

As most people who've had any elementary heat transfer course are aware, when insulating a pipe, wire, etc, there is a critical thickness for the insulation below which it causes greater heat transfer ...
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2answers
886 views

What is more efficient: Add milk, and then heat up coffee in the microwave, or microwave than milk?

Adding milk first increases the volume to heat and lowers average temerature, but adding it afterwards seems to have similar effects. How can you compare the two?
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219 views

Is there any optical component that uniformizes the incoming light?

Is there any optical component in existence that uniformizes randomly pointing rays?
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3answers
307 views

Is there really such a thing as an irreversible process?

If an isolated system goes from a state A to B, will it always eventually fluctuate back to state A? If not, give an simple example. Is it right to say that entropy only says that the probability ...
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1answer
169 views

What is meant by boiling off electrons in a heater coil?

In my electricity and magnetism course, we used a Thompson tube to produce an electron beam. There is a heating element at the back of the tube and the lab manual claims that "electrons are boiled ...
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1answer
145 views

Uncertainty and Thermodynamics

Dilemma The uncertainty principle of energy and the 2nd law of thermodynamics don't add up : the uncertainty principle of energy says that $\Delta \tau \cdot \Delta E \ge \frac{h}{4\pi} = ...
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4answers
416 views

Irreversible expansion and time reversal symmetry

Suppose there are N non-interacting classical particles in a box, so their state can be described by the $\{\mathbf{x}_i(t), \mathbf{p}_i(t) \}$. If the particles are initially at the left of the box, ...
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1answer
34 views

Unmixing of gases: What is the relevant temperature for my Entropy?

This answer to a question about unmixing gases states: However, let us now assume we have to hand a source of mechanical work, and a large heat reservoir at temperature $T$. I'll assume that ...
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Determine change in entropy - Please verify [closed]

Suppose 30 gram of metal gallium melts at 36°C. The melting temperature is 29.9 °C and specific heat of fusion is 80.3 kJ/kg. Explain if the melting of the gallium in this process is reversible or ...
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3answers
213 views

How “things” radiate electromagnetic radiation? [closed]

How things radiate electromagnetic radiation? I don't ask why they radiate (higher temperature than 0K) but how they radiate this electromagnetic waves?
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4answers
1k views

How slow is a reversible adiabatic expansion of an ideal gas?

A truly reversible thermodynamic process needs to be infinitesimally displaced from equilibrium at all times and therefore takes infinite time to complete. However, if I execute the process slowly, I ...
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3answers
807 views

Best way to chill a cup of coffee with cold water and 5 minutes [duplicate]

Initial data 1 x 3/4 full cup of hot coffee / tea / your favorite morning beverage cold water 5 minutes Considering that it's starting to get hot outside, and we all want to drink reasonably cold ...
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6answers
7k views

Is “dark clothes for winter, light for summer” relevant?

We are told to wear light clothes in summer as they are better at reflecting sunshine and keeping us cool. And dark clothes absorb sunshine and keep us warm. But is it really relavent? If I buy ...
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5answers
6k views

If I take a bottle of air into space, and open it, where does it go?

It seems to me that space doesn't have any/much air, and if my bottle is full of air, when I open it, where does the air go?
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3answers
2k views

How long does it take an iceberg to melt in the ocean?

This is a quantitative question. The problem is inspired by this event: On August 5, 2010, an enormous chunk of ice, roughly 97 square miles (251 square kilometers) in size, broke off the Petermann ...
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1answer
231 views

Will entropy continue to increase even if the universe begins to contract?

If the universe is heading for a big crunch, when the universe starts to collapse will entropy decrease and the arrow of time consequently reverse or not? I'm interested in the explanations, not just ...
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1answer
461 views

Modification of Newton's Law of Cooling

Yesterday I randomly started thinking about Newton's Law of Cooling. The problem I realized is that it assumes the ambient temperature stays constant over time, which is obviously not true. So what I ...
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2answers
905 views

How much more energy does it take for a human body to heat 0C ice vs 0C water?

I'm trying to determine if going through the trouble of ingesting ice is worth the hassle versus ingesting ice-cold water, but my physics skills are rusty. If I drink a gram of ice water at ~0C, my ...
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5answers
546 views

Is speed an intensive property?

I remember being taught in elementary physics that while it makes sense to add volumes, masses, or heat, it makes no sense to add temperatures. As I wanted to use that to illustate some other issue, ...
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2answers
189 views

How do greenhouse gases trap heat?

I am looking for a molecular-level understanding of the greenhouse effect. What is it about the carbon-dioxide molecule (and methane, and water, etc) that is different from other gasses ...
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4answers
4k views

What equation of state is needed for liquid states?

I'm familiar with the ideal gas law $$PV=nRT$$ but I don't think it applies to liquids like water. If I'm wrong, please correct me! If I'm right, then what equation of state applies to liquids such ...
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2answers
1k views

Why isn't water running faster hotter?

I was running the washing up water this morning, and started to think about why the cold tap isn't hot, and why the water doesn't get hotter the faster it is flowing (if anything, the cold tap gets ...
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2answers
621 views

Is there a phase transition between a gas and plasma?

Does a phase transition occur as a gas is heated to create a plasma? If so, is this a first or second order phase transition? Also, does the presence of a phase transition depend on the pressure or ...
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5answers
2k views

Can I take heat from the air and convert it to electricity?

Its a summer day and the air in my house has been heated up. I could switch on my air conditioning, but then I'd be using energy from the grid in order to reduce the amount of energy in my house. ...