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13

The low-entropy initial state of the universe is an open problem without a satisfactory answer. Your question is the first time I've heard the suggestion that the initial state should have been a crystal; you remind me that the quark-gluon plasma, which was the state of the universe while it was too hot for nucleons to be stable, has been shown to be a ...


11

Now I am left wondering why does the heat become lost as if travels slightly. It is not lost. It is spread more out. If you stand so close to the heat source that you are hit by, say 1/10 of it's radiation (1/10 of all photons sent out hit you), then when standing further away you are maybe only hit by 1/100. The heat radiation sent from the source ...


8

the two paradigmatic cases that illustrate these two possibilities is a gas, for the first, and a crystal for the second. Paradigms and examples are well and good, but be careful not to assume they are the only possibilities. In particular, black holes have entropy -- a lot of entropy. In fact they saturate the Beckenstein Bound. The entropy of a black ...


6

I suspect this will be closed as "opinion based". I don't believe there is a canonical answer. Usually microscopic scale relates to phenomena that occur on a level much smaller than the system under consideration (atoms in a crystal when you are thinking about the crystal, for example). There is an analogy with micro- and macro-economics. Micro-economics ...


5

This is such a complicated question! The worst part is that as heat leaves the chimney, it draws air from the room with it - air that needs to be replaced from outside. This actually makes fires quite good as ventilation systems. Whether a fire heats a building depends in very large part on the degree to which cool air can flow past parts heated by the ...


4

What I will state is speculative and based on the statistical mechanics derivation of entropy, and just the way I view it and do not consider that there exists a problem. After all thermodynamic theory emerges from the underlying statistical level of atomic and molecular interactions. where p_i is the probabability of microstate i. Setting aside quantum ...


4

The black hole initially lost the gravitational energy that was needed to create the pair. The pair-creation model is a bad description of Hawking radiation, which for macroscopic black holes is really photons. The second particle that gets created above the event horizon doesn't have nearly enough energy to escape. It does, however, produce photons above ...


3

No, you cannot prove that mathematical law. All you can say is that your experiments are consistent with your premise. I recommend you take the time to read some introductory books on physics, statistics, and the scientific method (which is to say, don't just take my word that my initial statement is valid).


3

In fact it's quite the opposite : cold places in a room are due to contact with the cold outside : door, window, bad isolation ... So putting heater here make you also heat the outside, and waste some money. The reason to do so is that the point of a heater is to make cold places hot : as you said you want an uniform temperature.


3

The heat simply disperses and the further away from the heat source you get the more space the heat has to disperse into


3

This is an excellent question, but not readily answered, as discussed in Floris's Answer. Here is a stab at how to get an estimate of efficiency. It is the method which I believe is reasonably accurate: the actual values will need to be refined by experimental measurement: I am not too confident of the actual numbers that fall out owing to the ...


3

The heat radiates away from the source equally in every direction (until it hits something). Imagine the sun. It is roughly spherical and radiates energy (some as heat) in all directions. The energy is radiated in a sphere. As the energy travels away from the source (the sun) the sphere expands but the amount of energy remains the same. When the sphere is ...


3

Joule's law, and thermodynamics in general, is a model of the classical world. Here, classical should be interpreted as non-quantum-mechanical. Thermodynamics is the study of large collections of particles and their collective behavior. No microscopic model is assumed, and one tries to extract as many (non-trivial) features as possible based on purely ...


2

That's a very hard question to answer with the appropriate level of detail! Very broadly speaking in an ideal metal all atoms are forming a perfectly regular crystal lattice. Conduction band electrons can move freely around these atoms, which makes it easy to pass a current trough the metal. In a (theoretical) metal with perfect crystal lattice the ...


2

Actually, there is a reversible process that will allow you to end up with a larger temperature, and this does not violate the second law. To see this, you can couple your system to Carnot engine, which will extract and "store" work until both the reservoir and the case are at the same temperature. Now use the stored energy to heat the case. Actually your ...


2

The answer is, it depends on the type of fireplace you have. An ordinary brick chimney consisting of a fireplace directly venting up and to the outside has a very low efficiency. The draft generated by the fire pulls warm air from the house, and most of the heat travels directly up. There are various types of fireplaces which specifically attempt to ...


2

The simple answer is the inverse square law which states that the intensity (power per unit area) of a heat source drops off with $1/r^2$ where $r$ is the distance (assuming a point source). Looking at your camp fire: imagine people standing side by side around the fire. Each gets a share of the heat. When they make the circle wider, more people can get ...


2

Physics is not mathematics. Physical laws are not axioms. A physical theory is not the derivation of all possible hypotheses from a set of axioms. Please repeat this like a mantra a hundred times a day for the next three weeks. Instead a physical theory is patterned as a set of naive ontological assumptions about the approximate usefulness of a set of ...


2

In short, ice-cream is a solid, but it is filled with air bubbles. All this air that was incorporated in the ice-cream as it froze (through various industrial processes) means that the dairy product doesn't freeze as a solid, but rather a foamy delicious treat. There are many websites explaining what it actually is, and how it is made, such as this one. ...


2

Roughly speaking solid matter is on a lattice form, A three-dimensional lattice filled with two molecules A and B, here shown as black and white spheres. The molecules fit like LEGO , the forces tying them together are mainly the spill over electric field forces , attractive and repulsive forming the patterns of the lattice. In a single crystal one ...


2

The type of blankets is not defined, different can mean many things. If one makes two classes, more insulating ones and less insulating ones the answer of Photonicboom applies. The more insulating one next to the skin will give a comfort value sooner than the less insulating one because the body will have to heat up a smaller amount of matter (air and ...


2

In a still air environment, the previous answers are correct and sufficient. In an environment with unheated air moving over you, however, the answer greatly depends on what blankets you have, exactly. Humans lose a lot of body heat to evaporation of sweat, so the amount of air passing across you makes a big difference in how warm you stay. Let's play a ...


1

Whilst I'm not sure that I disagree with what has already been written, I think that there is another variable - the temperature of the ground. I do a lot of cold weather camping, and it doesn't matter how thick your sleeping bag is, if you are not properly insulated from the ground with a thick sleeping mat, you get cold. Presumably this is because heat ...


1

Work is force acting over a distance. That means there can only be work done on the gas if the piston moves, i.e. if the gas changes volume. In that case, $W = \int F \text{d} x = \int P\, \text{d}V$, where P is the pressure difference between the inside and outside of the calorimeter. Note, however, that in your example the gas is doing work on the ...


1

According to p. 303-304 of the book Gravity from the Ground up by physicist Bernard Schutz, viewable on google books here, it's because in terms of the pair-production explanation for Hawking radiation, one member of the pair actually has negative energy and thus causes the black hole to lose mass (negative mass/energy falling into a black hole can also ...


1

Let's break up the process into two steps, which necessarily must happen in sequence--the first step is one in which the reservoir heats the body up from a temperature of 273 K to its own temperature of 363 K, and the second step is one in which the reservoir heats the body from 363 K to 373 K. The first step involves a positive entropy change, so it can ...


1

On the long run both scenarios will be equally as comfortable. However, when you initially cover yourself, you would want to cover urself with the thicker blanket first, so that you restrict the movement of air as much as you can, and thus warm up a few seconds faster. This is key because your body will warm up the air directly above your skin and the thick ...


1

Thermal expansion from an atomistic perspective: The energetic potential between two atoms can be approximated by two exponential functions, one for the attractive force between the atoms, one for the repulsive force. The superposition of these two force fields has a minimum at a certain distance. Examples for such empirical potentials are Stillinger-Weber, ...


1

I’m not sure I fully understand the question but I’ll try. The “curious one” says that if the initial condition is picked at random then it should be a state of thermal equilibrium (maximum entropy) since the overwhelming majority of states look equilibrium-like. Now there has to be something wrong with that in the cosmological context. States of thermal ...


1

I can help you with turbine part of your question. Turbines are employed to derive work in a power cycle. The choice of working fluid doesn't solely depend on turbine alone, you have to consider whole power cycle. For example in Rankine cycle (power cycle employed in Power Plants), water is widely used due to its thermodynamic properties(like high specific ...



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