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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1answer
68 views

Effect of breeze on a very hot day [duplicate]

If air temperature is well above body temperature eg air temp of 50C then would a wind make the apparent temperature higher or lower. Clearly the wind would help take away heat due to increasing ...
1
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2answers
107 views

Heating suprecritical water in a closed water tank

How does the pressure of water in a closed tank evolve in the following setting: - closed tank of 2 liters (filled up with water) - water initially at 25°C and pressurized to 3 bars The water is now ...
0
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1answer
84 views

Which laws of physics does this problem break?

One of the problems from the Google Code Jam programming competition, round 2 2015, goes like this: A kiddie pool is a big container in which you can put water, so that small children can play ...
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2answers
134 views

Definition of an irreversible process

I'm a little bit confused as to why quasi-static process cannot lose energy to friction in order to be reversible. This is how I'm thinking: Suppose you have a container of gas with a piston, and on ...
6
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3answers
7k views

How hot can metal get in sunlight? [closed]

I will make some 5mm blackened steel letters for a building. Now, in the sunlight in summer, how hot can they get? EDIT: i want to place some LEDs on the back of the letters. now the question is if ...
1
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1answer
61 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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0answers
33 views

Is it impossible to find the exact analytic form of the molar volume of liquid and gas in phase transition from the van der Waal equations?

I want to find the molar volume $v_g , v_l$ of gas and liquid respectively in the coexistence curve of phase diagram with given temperature when ideal van der Waal gas $$ P = \frac{RT}{v-b}-\frac{a}{...
7
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1answer
69 views

Integrated Boltzmann equation for dark matter

In Dodelson's book, the equation for a scattering process $ a + b \Leftrightarrow c + d $ is given as \begin{align} a^{-3} \frac{\mathrm d (n_a a^3)}{\mathrm d t}&=-n^{\text{eq}}_a n^{\text{eq}}...
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1answer
143 views

Why does the temperature of a gas inside a moving container not increase with velocity?

A rectangular (simplified) container with rigid surfaces, has a certain mass of ideal gas within it, and it accelerates in free space, undergoing rectilinear motion. There are no dissipative forces. ...
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1answer
119 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 ...
0
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3answers
6k views

Which materials absorb heat?

Which are the materials that absorb heat? and can i somehow convert that absorbed heat into a different form of energy? I am looking into trying to absorb the wasted heat dissipated by laptops,severs ,...
1
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1answer
26 views

does the internal energy and enthalpy of the GAS changes in a free expansion process?

when a balloon kept in an evacuated room is punctured and the ideal gas in the balloon goes on to fill the entire room,does the gas perform any work in this expansion, and is there in any change in ...
1
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1answer
61 views

Seeking Reference on Transport of Momentum by Diffusion of Mass

I'm looking at continuum mechanics from the perspective of De Groot and Mazur's "Non-Equilibrium Thermodynamics" - the first reference that I've come across that seems to do a good job of bringing ...
0
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1answer
48 views

Can gas return back into a sparkling beverage on cooldown?

We all know that if a sparkling beverage (let's say, CocaCola) spends some time outside of the fridge and gets warm, the gas comes out of the liquid, rises the inner pressure and makes the bottle ...
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0answers
20 views

Increased pressure of Liquid Pitch and Limestone (Bitumen/Asphalt) @ approximately 300 degrees Fahrenheit

If liquid pitch and limestone (20/80 mostly limestone) is pumped (appx. 5 gpm) out of a nozzle that restricts the flow compared to the flow that would be achieved straight out of the pump ( no ...
0
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1answer
270 views

Electromagnetic cooling

Heat means stored kinetic energy in matter. Microwave owens and induction heaters works on increasing kinetic energy on matter. Is it possible to make inverse of this heaters like cooler. Can we ...
2
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3answers
147 views

Different materials have different temperatures?

Why do two materials, under the same weather, have different temperatures? I have a small clue about it. For example, iron and wood supposed under the sun's radiation, and if we touch both of them, ...
0
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0answers
27 views

Work done by a gas in an expansion [duplicate]

1) Consider a gas expanding quasistatically and reversibly from $V_1$ to $V_2$ at constant temperature. I want to calculate the work done. So by convention work done by a system is a negative quantity ...
2
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2answers
903 views

what is the temperature (and pressure) of the oxygen inside an oxygen bottle?

In the hospital or in a lab, one can see the huge oxygen bottles. A question is, what is the temperature of the oxygen inside the bottle? And what is the pressure inside? We know the critical ...
1
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1answer
51 views

Find the velocity of the escape of the bullet

A gun has a muzzle 0.8 meters long and with a diameter of 0.006 m. A bullet with mass 0.002 kg is initially 0.01 m away from the end of the muzzle. As a result of a gunshot, the pressure of the gas ...
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0answers
44 views

Specific heat at constant volume

Me and my friend came across this derivation is some lecture notes of our thermal physics module. We have been trying to calculate the partial differential of the internal energy but cannot get the ...
0
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2answers
84 views

derivation qm canonical ensemble

In classical mechanics the canonical ensemble can be derived from the microcanonical ensemble of two systems in weak interaction. Is a similar thing possible in quantum mechanics? Is there any good ...
1
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1answer
48 views

Struggling with whether its $\pm p dV $

I am struggling to understand when calculating the work done by a gas whether it is postive or negative p. It my notes and in many other notes sometimes it is $-pdV$ and sometimes it is $pdV$. I ...
-1
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1answer
68 views

entropy change during irreversible heat loss [duplicate]

When a thermodynamic system gains heat if the heat gain is irreversible then there is a entropy generation along with the entropy transfer..so is there a similar entropy generation associated with ...
0
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2answers
70 views

clausious inquality

Take a reservoir which gains a heat Q irreversibly at temp T from a surrounding at temp T0 then the entropy change of reservoir is given by Q/t and that of the surrounding is -Q/T0...How is this right....
2
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1answer
141 views

Why the heat capacity doesn't diverge in the Kosterlitz-Thouless (KT) phase transition?

The KT transition has a special properties that, during the phase transition the heat capacity stay finite (so the behaviour of the heat capacity cannot reflect any critical behaviours). However, the ...
0
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1answer
253 views

Show that change in internal energy equals zero for an adiabatic process with incompressible fluid

I have a problem when solving an exercise in thermodynamics. I am supposed to show that when we have an open system, where the process is adiabatic with an incompressible fluid, it follows that the ...
1
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1answer
207 views

Helmholtz Free Energy vs Gibbs Free Energy in Landau Theory

When I was studying thermodynamics potentials for the first time, I learned that keeping the pressure and the temperature constant, the Gibbs Free Energy is a minimum, also, if we maintain the ...
0
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1answer
80 views

Changing the melting point of ice

Myself and a friend have been stuck on this problem for a while now. We know that we should end up with an answer of $-0.007K$ however, cannot get to this solution. Help with the method we should use ...
2
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1answer
200 views

Bernoulli Equation for isentropic ideal gas flow

If one derives the Bernoulli Equation for the isentropic ideal gas flow you get: $$ \frac{1}{2}v^2 + g z + \left(\frac{\kappa}{\kappa -1} \right) \frac{p}{\rho} = const. $$ Two questions: Is ...
3
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0answers
107 views

What liquid would wick away heat most quickly?

I've read and seen on various "life hack" websites that if you've forgotten to chill drinks, wrapping them in a wet paper towel and sticking them in the freezer for a few minutes rapidly cools them ...
1
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2answers
2k views

Why bodies lose heat faster in water than in air?

A simple question. In several places, including this very recent and already famous paper http://www.sciencemag.org/content/348/6236/786.short it is stated that bodies lose heat in water very fast ...
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2answers
330 views

Fan Speed Formula

Is there any formula for computing fan speed by using air mass,air flux, air density or specific heat? I have computed air mass and air flux, and found the values for air density and specific heat, ...
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0answers
41 views

Thermal Equilibrium of two thin sheets

While reading Gibbs' Elementary Principles in Statistical Mechanics I came across this footnote: The most simple test of the equality of temperature of two bodies is that they remain in ...
0
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1answer
272 views

Pressure, density, volume and mass in a room

Here's the question. A window in the room is open. The next day, the temperature of the room has increased, but the pressure of the air stayed the same. State and explain what has happened to ...
13
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1answer
449 views

How hot would tritium water be?

I realize this is kind of a silly question, but if you have tritium water, with the tritium half life of 12.5 years, I expect it would be quite hot. (note, this is not a homework question, I'm just ...
1
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1answer
108 views

Triangular cyclic process [closed]

I am currently studying for my physics exam and I am trying to wrap my head around cyclic processes. There is the cyclic process: We know its an diatomic ideal gas, and the following variables are ...
2
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1answer
1k views

Highest temperature possible to achieve using magnifying glass and sunlight [duplicate]

Temperature of the surface of the sun is about 5750K. Can you heat an object to more than 6000K using magnifying glass and sunlight? According to second law heat cannot be transferred from colder to ...
2
votes
1answer
223 views

Why should slope of pressure versus volume always be negative?

I read that the slope of the pressure, ($P$), versus volume ($V$) graph should always be negative for thermodynamic stability, but there was no further explanation in the text. Could someone give an ...
0
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1answer
275 views

Transfer of heat through a finite temprature difference

Consider the following derivation There are two reservoirs at temp A & B at temp T1 & T2 .They are connected by a metal rod such that T1 > T2. Q amonut of heat is transfered ...
2
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3answers
185 views

Feasible way to cool water (ice) to temperatures around -20 degree celsius

Is there an easy way to cool water to temperatures around -20 or -30 degree celsius that is economically and technologically feasible for a high school student. Can it be done using typical household ...
-1
votes
1answer
130 views

entropy change during heat loss

When a thermodynamic system gains heat if the heat gain is irreversible then there is a entropy generation along with the entropy transfer..so is there a similar entropy generation associated with ...
4
votes
1answer
418 views

Is it possible to build an air compressor with no moving parts? [closed]

Is it physically possible to build an air compressor with no moving parts? A thermodynamic cycle capable of compressing air with no moving parts and operate it in stationary way. EDIT I will add a ...
2
votes
0answers
77 views

Entropy Change for a Thermally Isolated System

Clausius' Theorem states that $\int\frac{dQ}{T}\leq0$ for a closed cycle, with equality for a reversible cycle. Suppose we wish to take our system around a closed cycle such that the path from A to B ...
2
votes
1answer
36 views

Is it safe and theorotically correct to heat a bar magnet using an open fire/furnace, provided conditions given below?

For a project, I will have to heat a bar magnet to any temperature above 40 degree celsius. For this, can I place the magnet over an open fire --like one in a furnace-- for 20 minutes or so to achieve ...
0
votes
1answer
68 views

Calculations on heat transfers [closed]

An unclothed person whose body has a surface area of 1.4m^2 with emissivity of 0.85 has a skin temperature of 37 °C standing in a 20 °C room. How much heat does the person lose per minute?
-2
votes
1answer
2k views

Does time freeze at Absolute Zero? [closed]

Time has many definitions per se, but the basic idea being it's "the measurement of change" so as we know, all matter looses it's ability of changing with the loss of kinetic energy. and the where it ...
1
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1answer
293 views

Entropy change in mixing two gases

The entropy change of an ideal gas is calculated as \begin{equation} \Delta S = C_V n\ln(\frac{T}{T_0}) + nR\ln{\frac{V}{V_0}} \end{equation} derived by integrating $dU = TdS - pdV$. It is only true ...
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2answers
88 views

What could be the effects of accidentally spilling supercooled water/liquid on an unprotected body surface?

Will the body rapidly start losing heat or will the water find a seed and solidify around it ?
1
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1answer
92 views

Classifying regions of Van der Waal like gas

Given the equation of state $$p+a\left(\frac{N}{V}\right)=\frac{Nk_BT}{V-bN} \tag 1$$ Taking into account of the fact that a realistic model requires $p \geq 0, V \geq Nb, N>0$ classify the ...