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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6k views

Function of air conditioner

What i always thought that air conditioners blow the cool air without knowing that they actually take the warm air from indoor and from outdoor. But whats the point of taking air from indoor and ...
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4k views

Why it is said that Universe is an isolated system?

I have read in many places "Entropy of an isolated systems never decreases" And as a corollary: "As Universe is an isolated system(I) then its entropy is constantly increasing(II)" I) ...
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1answer
12k views

How to calculate heat exchange/deltaT in a moving volume of fluid?

I am building a preheater for a maple syrup evaporator and am going to use the steam generated by the heating process to pre-heat the incoming sap from, say 5 degrees C to (hopefully) something on the ...
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1k views

cm^3/g as a unit of adsorption

I recently saw cm^3/g as a unit for amount adsorbed. Usually, you see either kg adsorbate/kg adsorbent or mole adsorbate/kg adsorbent. Does anyone know the meaning of this unit?
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354 views

What happens to internal energy in high-density materials?

Normal-density materials have internal energy, which is the sum of the average energies associated to each of the degrees of freedom. Degrees of freedom can be described as vibrational, translational, ...
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2k views

Extracting heat energy from a material

Does it violate any physical laws to take a portion of the energy out of a system and use it? Specifically I'm referring to heat. (Kinetic energy). For example, if you have a material which has a lot ...
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3answers
59 views

Is the internal energy of an ideal gas always $\frac{3}{2}nRT$?

Is the internal energy of an ideal gas always $\frac{3}{2}nRT\,?$ I saw in Wikipedia that it is $\alpha nRT\;.$ Is $\alpha$ always equal to $\frac{3}{2}$ for an ideal gas?
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62 views

Is this SISO (single input single output) or MIMO (multiple instead of single) system?

If I transform wave equation for vibrating string Mx′′+Cx′+Kx=b(t) in linear system using $x_1(t)=x(t)$ and $x_2(t)=x_1^{'}(t)$ vibrating string equation becomes $Md_tx_2(t)+Cx_2(t)+Kx_1(t)=b(t)$. ...
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39 views

Force over Area diagram [closed]

In this question a have to draw a F/A diagram in function of p-V (pressure-volume) diagram below. I think in a intuitive way that this graphic of F/A it´s going to be the same graphic because ...
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1answer
32 views

Cold Atom Hot Atom 2: Minerals Attracted to Heat

In electric hot water tanks why do calcium quickly form on the heating elements? I watched some one put in a new element. An hour later it stops working. Just to check he took the element and it had ...
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1answer
43 views

Why do i see more steam coming out from the vessel containing water after i turned off the stove? [duplicate]

It is a little observation i did when i was boiling the water. what i observe is that when i turned off the stove on which the water was boiling i could see more steam coming out from it than the ...
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36 views

Can outgassing produce a significant thrust on a space ship?

There are a variety of materials that outgas in the atmosphere, and I imagine they would do so even more in the vacuum of space. I imagine an object in space would experience a small force as ...
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50 views

If two gasses are in thermal equilbrium, do their molecules have same amount of Kinetic energy?

If two gasses are in thermal equilbrium, do their molecules have same amount of Kinetic energy?
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1answer
32 views

How does conduction happen?

I'd like to ask you how does conduction happen ? I mean, the atoms vibrating more hits the less vibrating atoms and gives energy. But how is that energy transferred ? For atoms to collide they must be ...
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95 views

When a gas is compressed by a piston, where is the heat added to the gas?

Suppose an ideal gas is being compressed by a piston inside a cylinder in an adiabatic compression process. Does the gas closest to the piston heat up first as the gas molecules collide with the ...
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43 views

How could be modelled this heat transfer problem?

I have been puzzled the other day by a young boy who asked me about the phenomenon making that, when arriving to the shower, water is cold. Simple, isn't it? I started describing, in simple words, ...
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3answers
46 views

How do you calculate oxygen temperature as atm pressure changes? [closed]

I know that when gases are decompressed the atoms suddenly have a bunch of space and absorb all the heat around them thereby giving the effect that it is cool but how do you calculate this for oxygen ...
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1answer
67 views

Compression vs. Friction - what happens when space objects enter earth's atmosphere

When reading about what happens when cosmic debris enters the earth's atmosphere, some sources say friction, others say compression. For example: On space.com it says: Meteor showers occur when ...
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1answer
31 views

Does a ceiling fan air heat up the air?

I was laying in bed one day, looking at my ceiling fan, when I wondered, "Doesn't the ceiling fan, because it makes wind, cause wind chill, which 'wicks' heat away from me -> making me feel cooler, ...
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1answer
52 views

Physic explanation of some property of heat equation? [closed]

When I compute the heat equation, I found that gross of heat do not change,it is same as our real world.But as I know , the heat equation is found according to the way of heat conduction. Why the ...
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1answer
38 views

Ideal gas law with two types of gases

Suppose a container with volume $V$. If I put 2 different types of monoatomic ideal gas, say type $A$ and type $B$, such that there are $N_1$ particles of gas $A$ and $N_2$ particles of gas $B$, with ...
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2answers
38 views

Hot Object In a Cooler Space [closed]

How would you calculate the heat given by an object that is hotter than its surroundings? I know there's Newton's Cooling Law, but what about any heat given off by radiation? Are these additive ...
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1answer
104 views

Why is it so hard to explain that the Brownian Ratchet doesn't work?

The Brownian Ratchet stood up to a lot of scrutiny before it was finally shown why it would not work as a perpetual motion machine, but it seems weird to me that all of that was necessary. If the ...
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1answer
86 views

Discrete time simulation of gas liquid equilibrium in a tank

I am trying to write a discrete time simulation of liquid/gaseous oxygen in a pressurised cryogenic fuel tank. For now I am assuming that the only external change to the system is the influx of heat ...
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1answer
52 views

How to calculate max temperature craft needs to withstand near the Sun

The Solar Probe Plus fact-sheet states that the craft will approach to the distance of 9 solar radii to the surface of the Sun (Approx 6.26e6 km) and its heat shields must withstand 1644K of heat. I ...
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1answer
51 views

Temperature of system in canonical ensemble

Upon reading Reif's explanations relating to systems exchanging energy and the canonical ensemble (Reif, Fundamentals of statistical and thermal physics, p. 95ff and p. 202ff), I am led to conclude ...
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1answer
26 views

Water's Specific Heat Capacity as an Outlier

Can the specific heat capacity of water being ridiculously high as compared to other substances be explained at a molecular scale?
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1answer
52 views

How is one process reversible and its reverse non-reversible?

My textbook gives this example of a reversible process: A gas in a piston is expanded over a long period of time, sitting on a hot plate that maintains its temperature. As an infinitesimal amount of ...
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1answer
52 views

Heat capacity of solids

In the Einstein/Debye models, the specific heat capacity goes as T^3 at low temperatures and approaches the Dulong-Petit law at higher temperatures. I undestand that some molecular motions (rotation, ...
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1answer
96 views

Confusion about heat capacities at constant volume and constant pressure

Let's take water for an example: the specific heat for water vapor is 1.99. This would mean that the molar specific heat is the molar mass times the specific heat (or $18.0*1.99 = 35.8$). Is 35.8 ...
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56 views

Formation of bonds and heat release

We know when there's formation of bonds during chemical reaction there's heat release to the surrounding due to conservation of energy. But what I am confused about, is the kinetic energy of the ...
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1answer
56 views

How to find the variation in temperature at a certain point inside a body undergoing heat transfer via conduction?

I am trying to find a way with which I can find out the temperature of a certain point inside a body undergoing thermal conduction. I understand that this might not be very simple to calculate since ...
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1answer
45 views

Does venus have plasma in its atmosphere?

Is it hot enough on Venus for thermal collisions to ionize molecules? If not, what temperature would it have to be?
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1answer
136 views

When i tear a paper, can i accidentally create nuclear fission?

I know it's a stupid question... but when I tear a paper i may coincidentally split it and create nuclear fission. When i tried experimenting, by tearing the paper for HELLKNOWS how many times, I ...
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1answer
79 views

Why does a cloud form around ice cream?

Everyone have probably seen the phenomenon as one opens a cool ice cream from its pack, a white cloud begins to flow around the ice cream surface, and it constantly spreads out until the ice cream ...
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1answer
145 views

Why is Cv used in the adiabatic expansion of Carnot Cycle to calculate internal energy

When I took this class years ago, I simply accepted it as fact. However, now that I'm teaching it, the following bugs me....a lot. Why do they use Cv to describe the change of internal energy during ...
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3answers
116 views

If heat can't be transformed into other forms of entropy, why do hot things radiate electromagnetic waves?

The laws of entropy says entropy can only increase. On the other hand, if I take a hot object, it will naturally convert its heat into EM radiation. How is this possible? Does EM radiation count as ...
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1answer
81 views

Reversible cycle approximated by Carnot cycles

My textbook, W.E. Gettys, F.J. Keller, M.J. Skove, Physics 1, gives the definition of a reversible transformation as a transformation that can be inverted by effectuating only infinitesimal changes in ...
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2answers
136 views

Paradox of potential energy of gas molecule

We know that when water is heated at its boiling point, it will become vapors. Then because there is no change in temperature, the heat supplied will be transferred to the potential energy of the ...
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2answers
70 views

What is the perfect Ice Cube? [closed]

I have a freezer with -25°C temperature and Soda with +30°C. What is the ice-cube-sized material I can put in the freezer that can bring my glas of soda to the lowest temperature? Are e.g. saltwater ...
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1answer
98 views

canonical ensemble that is quantum mechanical and continuous?

I do not understand what the following statements from Wikipedia mean For a canonical ensemble that is quantum mechanical and continuous, the canonical partition function is defined as $$ Z = ...
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4answers
153 views

Really how does the entropy of the universe increase?

Universe means the system along with its surroundings. I have always got this statement while studying the second law; be it a thermodynamics book(Sears, Salinger) , physical cihemistry book(Atkins, ...
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2answers
59 views

Finding the Enthalpy of an Ideal Gas given internal energy

I am trying to find a formula for tying things up. Given an ideal gas like helium or nitrogen gas (diatomic) how can I find its enthalpy simply given internal energy? I remember it was once taught in ...
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1answer
99 views

Preventing Heat Escape

Is is possible to completely prevent heat from escaping from a closed container? Here is a diagram of vacuum flask, which tries to implement the design - Vacuum Flask prevents heat from escaping ...
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2answers
77 views

Is possible to synthesize diamond at relatively lower pressures (6 to 7 GPa vs 12 GPa)?

Pure binderless nanopolycrystalline diamond can be produced from graphite when the graphite is treated with more than 12 GPa pressure and at least 2100°C temperature . If we treated graphite or ...
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1answer
52 views

Tap water in the cold glass

It is fairly long time I was in school and I was particularly bad at thermodynamics. This is an question I was trying to comprehend. I have 500ml of tap water @ 20°C. I pour it into heavy glass ...
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2answers
37 views

Deriving the partition function in MaxEnt

I'm trying to understand this paper on Maximum Entropy by Jaynes, and am stuck on something which should be rather simple. We're attempting to maximize the entropy $-\sum_i p_i \ln(p_i)$ subject to ...
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1answer
95 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 ...
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70 views

Charles Law inverse for cooling?

Is the inverse of Charles law also true? If I double the volume, the temperature will be halved? In the fire service we ventilate a structure by opening up the ceiling to the attic. If the volume of ...
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2answers
1k views

How long does it take for water to boil when subjected to intense heat?

I have a rather odd question that may just boil (sorry) down to a fairly simple problem I can't solve. The scenario is this: A person is testing the intensity of a super-focused beam of sunlight in a ...