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14

I will try to answer these questions from different views. Macroscopic view The "quantitative" rather than qualitative difference in a liquid-gas phase transition is due to the fact that the molecules arrangement does not change so much (there is no qualitative difference) but the value of the compressibility changes a lot (quantitative difference). This ...


9

For a pure substance that can exist in the solid, liquid, and vapor states (i.e., wood is not in this category), let's assume that a closed container is half full of liquid and half full of vapor. As the temperature rises, the liquid expands and the liquid density falls. Also, as the temperature rises, the pressure in the container rises due to the vapor ...


7

The many worlds interpretation has a lot of problems, but this isn't one of them. You're imagining "creating alternate universes" as some energetic event, like a mini Big Bang, but what really happens is a smooth splitting of the wavefunction. For example, suppose we have a spin in a superposition of up and down states, $$\frac{1}{\sqrt{2}} (| \uparrow \...


6

The temperature appearing the the Clausius inequality is definitely the temperature of the "boundary interface (with the surroundings)", or simply the temperature of the sources. One of the best places I have seen this discussion is in Fermi's book, chapter 5, section 11. He is explicit about it. To see this you have to recapitulate the steps in obtaining ...


4

Real world assumptions: No temperature gradients over the cross-section of the pipe. Plug flow (turbulent flow). Water heat capacity $c_p$ and density $\rho$ are temperature invariant. Consider an infinitesimal mass element $dm$ at temperature $T(x)$ travelling down the pipe at speed $v$. We apply Newton's law of cooling to it: $$\frac{dQ}{dt}=hdA\big(...


3

$1$ litre of water will remain almost $1$ litre as long as it is in the liquid state, no matter what the temperature is. The following formula gives you an order of magnitude estimate of the expansion: $$\Delta V=V_0\ \Delta T \ \beta$$ where $\beta$ is the coefficient of thermal expansion and $V_0$ is the initial volume. For water, $\beta \approx 10^{-...


3

The Earth+windmill system has conserved angular momentum. When the windmill starts spinning the angular momentum of Earth must change in response. However this change is marginal. Furthermore the windmill system will stop spinning when the wind dies down and this will restore the original angular momentum of Earth (when I say Earth I mean everything inside ...


3

The 'go to' partial differential equation here is surely the Heat equation (Fourier), here in one dimension: $$\frac{\partial T}{\partial t}=\kappa \frac{\partial^2T}{\partial x^2}+\frac{\dot{Q}(x,t)}{c_p\rho }$$ It can be easily expanded into three dimensions or expressed in polar, spherical or cylindrical coordinates. It's not clear from your question ...


3

Good question. I don't have my Widom around, but I'll try to answer from memory. I think the consensus is to say a substance is at its gas state if it could be a liquid at the same temperature. This, as opposed to same pressure, same volume, etc. If the temperature is supercritical, there is no transition between liquid and gas, and the generic term "fluid"...


3

Attempting to answer the "why" question intuitively: In a liquid, the molecules experience significant intermolecular force - so much so, that the average energy of the molecules is insufficient to escape the attractive force of the surrounding materials. The result is that it energetically favorable for them to remain close together, even if that means ...


2

I have no idea what you are asking in (1). (2) During adiabatic compression, the temperature of the system does change. Starting from the first law of thermodynamics: $$\mathrm{d}U = \mathrm{d}Q + \mathrm{d}W$$ For an adiabatic process $\mathrm{d}Q=0$. If we assume an ideal gas, then the internal energy is $\mathrm{d}U = C_V\, \mathrm{d}T$ and the work ...


2

Why does a critical point even exist? I think this question is equal to this one: "Why the width of the two phase region is bigger at lower temperatures and pressures?" Specific volume of liquids mostly depends on the temperature of them in comparing with their pressure. This means, for a well-defined increment of the pressure, we can neglect its effect ...


2

There are two definitions of entropy, which physicists believe to be the same (modulo the dimensional Boltzman scaling constant) and a postulate of their sameness has so far yielded agreement between what is theoretically foretold and what is experimentally observed. There are theoretical grounds, namely most of the subject of statistical mechanics, for our ...


2

Gold will compress to about half of its volume at atmospheric pressure if you compress it to 2 million atmospheres at room temperature, which is something that I'm sure has been done with diamond anvil cells. For many metals, the atomic lattice will also undergo structural phase transitions from one lattice type to another at certain pressures, but I don't ...


2

The relationship between thermodynamic and information entropy is still a work in progress. However, it is clear that he thermodynamic entropy is a rough measure of disorder, in the sense of not knowing in which specific microstate, all compatible with a given macrostate, the system is. Thus there is at least a loose relationship between thermodynamic ...


1

To calculate the amount of heat energy needed to heat a pot with its content of water we can use a simple formula: $$\Delta H=mc_p(T_2-T_1)$$ Where $\Delta H$ is the heat energy needed to heat an object of mass $m$ and specific heat capacity $c_p$ from $T_1$ to $T_2$. For a pot with water these energies would need to be calculated for both separately and ...


1

This is an interesting question and one that probably needs detailed simulation to settle. But one can make the following broad prediction: the shape of the meteorite would have minimal effect on the outcome, for the following reasons: At the kinds energies let slip in the moments of impact and the kinds of pressures and temperatures that prevail, all ...


1

You can wait three or four minutes and let the pressure drop or..... If you feel lucky you can try tapping the can a dozen times, as is shown on this video https://youtu.be/NQYO3Dp8lCA


1

Leaving this here for now... Will update with more information and references later. Einstein and Debye showed that specific heat is a function of temperature, but is asymptotic at high* temperatures. Here is a simple explanation why: Heat, with regard to everyday applications, is simply a measure of the motion of atoms and molecules. Let's start with ...


1

Influence of Magnetic Domain Walls and Magnetic Field on the Thermal Conductivity of Magnetic Nanowires http://pubs.acs.org/doi/abs/10.1021/nl502577y H.T. Huang et al., “Influence of magnetic domain walls and magnetic field on the thermal conductivity of magnetic nanowires,” Nano Letters, vol. 15, pp. 2773-2779, 2015.


1

From a biochemical point of view, heat detection is achieved by proteins at the surface of nerve cells. They basically just trigger a nerve signal above a given temperature. So they DO detect temperature and not a "heat flux". It may seem surprising that nerve cells react so quickly but the increase/decrease in temperature does not need to go all through the ...



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