Tagged Questions
1
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1answer
71 views
Does brown but transparent swimming pool water heat significantly faster than western style highly chlorinated pools?
Eastern European swimming pools are often brown tinted water. i was told it was the color of the chemical to keep the pools clean, but who knows. These pools did not smell unsanitary and may have even ...
0
votes
0answers
14 views
What is the effect of an increase in pressure on latent heat of vaporization?
What is latent heat of vaporization ($L_v$) in the first place? Wikipedia seems to indicate that it is the energy used in overcoming intermolecular interactions, without taking into account at all any ...
1
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0answers
48 views
Calculate how hot PLA will become
I am trying to attach the shaft of a brass heating tip to a PLA component. My problem is that the tip will have to reach a temperature of about 200°C and the PLA can only handle a temperature of about ...
-1
votes
1answer
44 views
Heisenberg's uncertainty and $0 K$ temperature
when a body is subjected to $0 K$ temperature, it becomes rigid. hence if we see in terms of quantum the lattice vibration decreases, resulting in no change in the direction of the Random velocity, ...
0
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0answers
30 views
Negative temperature [duplicate]
How can we prove that if a negative-temperature system is in contact with a positive-temperature system, then the heat flow from the first to the second (and finally, the temperature of the second ...
1
vote
3answers
131 views
Integrating factor $1/T$ in 2nd Law of Thermodynamics
How would you prove that $1/T$ is the most suitable integrating factor to transform $\delta Q$ to an exact differential in the second law of thermodynamics:
$$dS = \frac{\delta Q}{T}$$
Where $dS$ is ...
0
votes
2answers
89 views
How temperature gradient is a vector?
Everyone knows Temperature gradient is a vector quantity having direction from cold to hot.My confusion: why is temperature gradient vector if its direction is always fixed (as in the case of ...
1
vote
2answers
28 views
Heating and Recooling of an Object
Consider a piece of metal of length $L$ and linear thermal expansion coefficient $\alpha$. We eat the metal $\Delta T$ degrees, causing the metal to increase to length
$$ L' = L + L \alpha \Delta T$$
...
16
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6answers
1k views
Why isn't temperature measured in Joules?
If we set the Boltzmann constant to $1$, then entropy would just be $\ln \Omega$, temperature would be measured in $\text{joules}$ ($\,\text{J}\,$), and average kinetic energy would be an integer ...
1
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1answer
56 views
How long does it take a warm object to cool in air?
This is a work-related question. A warm steel torus of a given diameter & thickness is left in a room held at a controlled temperature, how long does it take to reach equilibrium? Assume the air ...
1
vote
0answers
43 views
How to solve state parameters using these givens for an ideal gas?
In a thermodynamic turbine using air as an ideal gas, given that you have a known inlet temperature value $T_i$, a known exit pressure value $P_e$, a known inlet and exit velocity $V_i$ and $V_e$, a ...
2
votes
2answers
133 views
Why the temperature is getting lower when the universe is expanding
As we know, if an ideal gas expands in vacuum, as its energy is unchanged, the temperature remains the same. An ideal gas's energy does not depend on volume. In general, the energy is $kT$ times the ...
4
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1answer
97 views
Does the Kelvin have a rigorous definition?
From Wikipedia:
The kelvin is defined as the fraction 1⁄273.16 of the thermodynamic temperature of the triple point of water.
That presupposes that we can take a fraction of temperature.
Now, ...
3
votes
2answers
136 views
What's the basic difference between heat and temperature?
Temperature is usually seen as a calibrated representation of heat but what about latent heat?
Eg. Ice and water have different amounts of heat at 0 degree c.
3
votes
2answers
173 views
Ideal gas concentration under temperature gradient
I'm trying to calculate the concentration of an ideal gas in an adiabatic container as a function of position where the top and bottom plates of the container are fixed at temperatures $T_1$ and ...
2
votes
1answer
103 views
Does electric potential have a temperature?
When I took my first thermo class a tucked away chapter introduced Exergy in terms of electrical energy, meaning that the amount of electrical energy you could get from something is functionally its ...
3
votes
2answers
135 views
With ideal gases, varying quantity of moles, and having a constant volume how do temperature and pressure behave?
I'm trying to build a simulation of gases so I ended-up trying to use law of ideal gases ($PV = nRT$).
In my scenario:
volume is constant ($V=1\rm{m}^3$);
a known quantity of moles are being added ...
3
votes
1answer
128 views
Why aren't two systems in thermal equilibrium the same as one system?
I am reading Molecular Driving Forces, 2nd ed., by Dill & Bromberg.
On page 53, example 3.9, we consider why energy exchanges between two systems from the point of view of the 2nd law.
We ...
2
votes
3answers
298 views
Less than absolute zero possible? [duplicate]
Possible Duplicate:
Temperature below absolute zero?
According to this article
http://www.sciencemag.org/content/339/6115/52 (preprint: http://arxiv.org/abs/1211.0545)
it is. What do you ...
8
votes
3answers
260 views
Could temperature have been defined as $-\partial S/\partial U$?
When coming up with a definition of temperature, it's typical to start with an empirical definition that a system with a hotter temperature tends to lose heat to a system with a colder temperature. ...
3
votes
1answer
115 views
How can gas from compressed air can “take” heat from surrounding environment?
I have recently been reading about why a can of compressed air gets cold when the air it contains is discharged. From what I understand the change from a liquid to a gas requires energy and therefore ...
5
votes
2answers
368 views
Temperature below absolute zero?
I saw this Nature article today, which cites e.g. arXiv:1211.0545.
And it makes no sense to me. The temperature of a collection of particles is the average kinetic energy of those particles. Kinetic ...
0
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1answer
216 views
How much energy Maxwell's demon will earn?
Suppose we have one mole of one-atom ideal gas at temperature $T$.
Suppose Maxwell's daemon has separated molecules into two sections, one with speed below mean and another with speed above mean.
...
1
vote
1answer
247 views
Liquid with freezing point above 0 Celsius that could be use at ice rinks
Please help me with an answer to my dilemma:
Is there a liquid that could be used to fill an ice rink (non-explosive, non-poisonous, etc), and have the freezing point above 0 Celsius?
3
votes
2answers
287 views
How to interpret Stefan-Boltzmann's law?
The Stefan-Boltzmann equation states $e=\sigma T^4$, but how do we interpret this?
Is this completely wrong: A body of size $s^2$ generates the radiation/temperature $T^4$ for a given size and a ...
4
votes
2answers
203 views
Is the proper interpretation of temperature missing in this book?
In Randall T. Knight’s textbook “Physics for Scientists and Engineers” in the first chapter on thermodynamics (Ch. 16: A Macroscopic Description of Matter) one of the first conceptual questions is ...
3
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2answers
229 views
What is temperature?
Recently I read an interesting article about negative temperature. I was puzzled because I thought before that temperature has definite meaning in thermodynamics: it tells about how fast atoms jiggle. ...
5
votes
1answer
101 views
Which came first, movement or heat?
According to my measly understanding of the universe, when particles hit one another, some of their kinetic energy is transformed into heat. But when we heat particles (for instance, putting a bucket ...
4
votes
4answers
212 views
Why can $\beta$ not be linearly proportional to $T$, that is $\beta = constant \times T$?
$\beta$ in statistical mechanics is equal to $\frac{1}{k_BT}$ in in thermodynamics, but I do not understand why $\beta\propto T^{-1}$ instead of, say, $\beta\propto T$?
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3answers
160 views
Temperature and density
As temperature rise the density become lower,When temperature goes down, density is higher but in higher temperature the body become bigger so why density become lower?
4
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4answers
4k views
The difference between heat and temperature
So as I understand it, heat energy of an object is the SUM of all the kinetic
energies of the molecules of the object (upto constant factor).
The temperature on the other hand is the AVERAGE of the ...
4
votes
3answers
128 views
Temperature of a gas (assumptions about the particle speeds)
Temperature is related to average of particles kinetic energy.
I would like to ask about a singular state of a particle system of a little time interval.
The question is:
If all particles were ...
5
votes
2answers
94 views
Why is the gas halo of the Milky Way so hot?
I have read on the webpage of NASA that there is a massive hot gas halo around our galaxy. Its temperature is between 100,000 and 1 million Kelvins or more. I do not understand why is it so hot. The ...
4
votes
1answer
129 views
Ideal gas and diatomic gas with same temperature
If a box of ideal gas and another box of diatomic gas are in thermal equilibrium,
does it mean that the average translational energy of ideal gas particle (A) is the same as that of diatomic gas ...
1
vote
1answer
243 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 ...
1
vote
0answers
96 views
“This is not a perpetual motion machine, because reservoir temperatures are changing.” Is it a valid argument?
I've already faced this situation several times: given a statement (in area of thermodynamics) I used it to provide an example of some perpetual motion machine (of first or second kind). Therefore, I ...
2
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2answers
681 views
Does negative temperature in Carnot cycle yield a counterexample of the second law of thermodynamics?
By Carnot Theorem, the efficiency of Carnot cycle is$$\eta=1-\frac{T_C}{T_H}$$
where $T_C$,$T_H$ are the absolute temperature of the cold reservoir and hot reservoir respectively. Since $T_C > 0$, ...
3
votes
3answers
741 views
How can I determine density of a gas only given temperature?
I have a homework problem where exhaust is traveling through an exhaust system (assumed to be air for simplicity) from and engine and then released into the atmosphere. The exhaust is at a temperature ...
2
votes
3answers
136 views
Heat Equation Equalities
While studying the heat equation, I ran into a few equalities that I cannot understand.
For example, Fourier's law of heat conduction claims that
$$\varphi(x,t)=-K_0\frac{\partial u}{\partial x},$$
...
0
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1answer
169 views
Dependance of temperature on color of metals
I asked this question because I supposedly did last year, Stanfor Klein which belongs to the Solar Energy Laboratory of the University of Wisconsin says that "the color of a car does not affect its ...
4
votes
3answers
436 views
Is temperature an extensive property, like density?
I was thinking about it some time ago, and now that I've discovered this site I would like to ask it here because I couldn't work it out then.
I know that the higher temperature the air in my room ...
5
votes
6answers
761 views
Is it theoretically possible to reach 0 kelvin?
I'm having a discussion with someone.
I said that it is -even theoretically- impossible to reach 0K, because that would imply that all molecules in the substance would stand perfectly still.
He said ...
1
vote
1answer
103 views
Temperature and latent heat
Building a bronze stature we make a mold and pour in the liquid bronze when the bronze hardens we remove the mold.
The mold is made of 3 Kg of steel and the statue has a mas of 1 Kg. The specific ...
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vote
2answers
138 views
Using CO2 to air condition a room
I'm trying to determine how much dry ice or liquid nitrogen I would need to cool 3300 cubic feet, about 90,000 liters of air, from about 100F (37.78C or 310K) to about 90F (26.67C or 299.81K). I'm ...
3
votes
3answers
331 views
Proof of existence of lowest temperature $0 K$
Im mathematics there is a concept of infinity meaning that whenever you pick a number and say that it is the smallest/Largest there is a way to further reduce/increase that number by ...
4
votes
1answer
491 views
The speed of sound is proportional to the square root of absolute temperature. What happens at extremely high temperatures?
The speed cannot increase unboundedly of course, so what happens?
1
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1answer
210 views
Thermodynamics, bullet fired into ice
I'm beginning to study basic thermodynamics and I want to solve this exercise:
It fires a lead bullet from $3g$ to $30^oC$ with a speed of $240\frac{m}{s}$ to a block of ice at $0^0C$. How much ice ...
1
vote
1answer
139 views
Calculating temperature of water in the freezer
Assuming water volume ($V$), initial water temperature ($T_0$) and environment temperature ($T_e$) are known, what is the easiest way to calculate temperature of water in given time ($T$)?
For the ...
0
votes
1answer
150 views
Mixing Water at Different Temperature
If I have cup of water at room temperature (say, $25^\circ$C). What would be the resultant temperature if I pour another cup of same amount of water at $100^\circ$C to it? Is it simply ...
0
votes
2answers
349 views
What is the physical or mathematical meaning of the Gibbs-Duhem equation?
The Gibbs-Duhem equation states
$$0~=~SdT-VdP+\sum(N_i d\mu_i),$$
where $\mu$ is the chemical potential. Does it have any mathematical (about intensive parameters) or physical meaning?
