# Tag Info

4

It is actually very easy to consider this. We don't need any models. we are blessed with a sizable rock at exactly 1 AU from the Sun, a rock with no trace of any atmosphere at all: Moon (Source: Wikimedia Commons) Temperatures on the moon vary from 70K to 390K. Average temperatures, depending on location, vary from 130K at the poles to 220K at the ...

3

For electric "resistive" heat, you have a point. Energy in equals energy out, so it shouldn't matter if you're heating your house with a 1000 Watt heater or ten 100Watt light bulbs: both should produce the same result. In practice, you have to worry about getting the heat where you want it. If the warm air all floats up into a layer on the ceiling, you'll ...

3

I will first elaborate what wind-gusts are not, for mental clarification: Thermodynamics as you may have encountered it in a physics course, is a static theory, as opposed to dynamic theories. More specificly that what is taught at university is usually equilibrium thermodynamics - You calculate the equilibrium state of a system where it will end up, but ...

2

This is a difficult question for many reasons. One reason is likely because most of the introductory thermodynamics textbook problems that we are familiar with from childhood do not involve gravity. To illustrate this difficulty with gravity consider, for example, this snippet from an article in the New York Times Review of Books by physicist/mathematician ...

2

It's an example of adiabatic expansion. If you have a container full of gas and you expand the container, the gas cools. Entropy is preserved. Adiabatic processes preserve entropy. Any decrease in entropy due to lowered energy, and correspondingly fewer possible velocities for the particles, is offset by an increase in entropy due to the expanding volume, ...

2

I thnk the answer to this lies in 'Chaos Theory', which can also be described as non-linear dynamics. To give an example of a simple linear system - if you want to travel from the West Coast of the USA to the East Coast of the USA by car travelling at an average speed of 60 miles per hour for 12 hours driving a day you can make a prediction of how long the ...

2

Even without quantum mechanics, the third law of thermodynamics only holds if there is a single lowest-energy state. For example, if there are two degenerate lowest-energy states, then the entropy is $k_B \log2$.

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Simple black body radiation theory (adapted from http://www.atmos.washington.edu/2002Q4/211/notes_greenhouse.html): The earth receives a certain amount of heat per unit area from the sun - this amount is about 1370 W/m$^2$ for parts of the earth facing the sun when there is no atmosphere. But the earth presents a "disk" with area $\pi R^2$ to the sun, when ...

1

If we consider temperature to be due to translational motion of the molecules and we assume the system has reached equilibrium, then the velocity distribution of the molecules is given by the Maxwell distribution: $$f(v) = \sqrt{\left(\frac{m}{2\pi k T}\right)^3} 4 \pi v^2 \exp\left(\frac{m v^2}{2 k T}\right)$$ which will give you the velocity ...

1

Intuitively, For a gas,if you apply heat to the container of gas the kinetic energies of the molecules or atoms increase,means heat added is used in increasing the kinetic energies of the molecules. As we know ,temperature of a gas depends on how fast the molecules of gas moving or vibrating ,so on heating temperature of the gas increases. Now these ...

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I think the wrong step was the assumption that entropy increases, where in fact maintaining the temperature would require a an outflow of heat, which means the entropy of the gas is decreasing. To see how this relates to your formula, notice that this decrease in entropy would also increase the enthalpy by the same amount, however enthalpy will also ...

1

Oil boils at a higher temperature than water which means that when water is poured into boiling oil it is heated to, and past, the boiling point very quickly. Oil is also less dense than water meaning that the water will sink to the bottom of the pot. Water at the bottom of the pot being heated very rapidly forms a gas at the bottom of the pot underneath ...

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Let me show you that there is no contradiction by pointing out e.g. that for ordinary expansion periods (that is away from first order phase transitions, decouplings...) the total entropy is actually constant in time while the universe is getting bigger and cooler. Or, going back in time, the universe is getting hotter while S is kept constant. How is this ...

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A negative solution like that is essentially just a sideresult from the mathematical method. You could consider your physical model as just a piece of a more general mathematical model. Solving the problem on the mathematical model then gives you all solutions; but only the solutions lying within the physical part of this model are actually solving the ...

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