Covers the study of (mostly homogeneous) macroscopic systems from a heat/energy/entropy point of view. Maybe combine with [tag:statistical-mechanics].

learn more… | top users | synonyms (1)

0
votes
0answers
29 views

Does a fixed amount of gas have slighty more mass when at a higher temperature?

According to relativity, energy and mass are equivalent. Does this mean that the energy added to a fixed amount of gas when it is heated adds slightly to the mass of the gas? The difference would be ...
2
votes
4answers
104 views

How can there be entropy change in this system?

How can there be an entropy change in this system? Suppose if I have a system consisting of liquid water, $1\, \mathrm{kg}$ at $290\,\mathrm{K}$, I stir it, and do say, $10\, \mathrm{J}$ of work on ...
0
votes
0answers
29 views

Determine the amount of energy used for baking a cake

Let's suppose we have a room of temperature $T_0$ with an oven of volume $V$, both filled with air of density $\rho$ and specific heat $c$. We need to bake a cake in the temperature $T_1$. Thus we ...
26
votes
1answer
2k views

Why do two flames kept side by side merge into a single flame?

I have read about why a candle flame is in the shape of a tear drop in the presence of gravity. The top portion which is sharp is directly above the wick, where the soot particles from the wick rise ...
-1
votes
0answers
19 views

What is the change in PSI of a football with 13.5 at a temperature of 77 degrees F when placed in a 23 degree environment? [duplicate]

The internal pressure of a regulation football is 13-14 lbs/square inch at 77 degrees (Fahrenheit). What pressure will it become when taken out of that 77 degree environment and placed in a 23 degree ...
1
vote
2answers
24 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 ...
3
votes
1answer
49 views

If entropy is a state function, then why is all the talk about reversible vs. irreversible processes?

So I'm preparing for my Thermodynamics undergrad exam, and I just can't wrap my head around the significance of reversibility vs. irreversibility of a process in relation to entropy. I mean if entropy ...
2
votes
1answer
418 views

If a microwave oven disk rotates to warm up food, why doesn't it go up/down/sideways?

This has been in my mind for a while... Well, actually everytime I heat any food with a greater amount of liquid in it: a microwave oven warms up food by inducing polar molecules in the food to ...
0
votes
1answer
41 views

Will an object with a higher temperature lose its heat faster than a cooler, yet warm object

I'm after the math, which I don't understand yet and can't find elsewhere. The variables are: Two identical cups, A and B The same volume of fluid is contained in each cup, test fluid is water. ...
-1
votes
2answers
50 views

If pressure inside a container is lesser than atmospheric pressure, how long can the vessel resist deformation? [closed]

Is the strain caused by stress (due to the pressure difference) is negligible?
1
vote
1answer
15 views

What physical change has taken place in a solid, say ice, half way through a latent heat temperature verses time experiment?

During the classic high school latent heat experiment a solid such as ice is heated from below the melting point until it is a liquid above the melting point. During this experiment the temperature ...
2
votes
2answers
416 views

Is there a highest temperature? [duplicate]

Im new to physics and do not yet know of all of the terms and math. I was wondering about temperature. I read that there is the lowest temperature which is absolute zero where nothing happens, i.e. ...
0
votes
2answers
42 views

Why specific heat at constant pressure is greater than specific heat at constant volume?

I know the relation between specific heat at constant volume and pressure and I also know how to calculate it. Thing is, I don't understand its concept I want to know why at constant pressure, ...
0
votes
1answer
52 views

How can we be sure the Maxwell speed distribution equation is always a rational number?

The Maxwell speed distribution equation is given as $$f(v) = 4\pi \biggl(\frac{m}{2\pi kT}\biggr)^{3/2}\exp\biggl(-\frac{mv^2}{2kT}\biggr)v^2.$$ The left hand side gives the fraction of molecules ...
0
votes
1answer
41 views

Why dU may not equals dW in free expansion?

From a video lecture, it is mentioned that "dU≠dW in Joule's free expansion if the process is irreversible and adiabatic" Mentioned in around 36:00-38:00 in the video: ...
2
votes
2answers
76 views

Resonance in Benzene violating Second Law of Thermodynamics

In chemistry a few months ago we were taught the resonant structure of benzene, that states the double bonds upon the six carbon atoms flicker back and forth between the two possible states it can be ...
0
votes
0answers
35 views

Filling an empty box with ambient air

A rigid box has a volume of $V_1$ and is thermally isolated so that it exchanges no heat with its environment. Initially the box is empty, and the air around it has a pressure of $P_0$ and a ...
0
votes
1answer
77 views

What happens as you approach/cross the Planck temperature?

According to IFLScience, above the Planck Temperature (absolute hot) conventional physics break down. My question is what happens as you approach this temperature, and, if it is possible, what ...
0
votes
1answer
32 views

Amount of heat required to raise the temperature of a balloon which requires no energy for expansion?

Two moles of ideal helium gas are in a rubber balloon at $30^°C$. The balloon is fully expandable and can be assumed to require no energy in its expansion. The temperature of the gas in the balloon ...
0
votes
1answer
47 views

Is the pressure uniquely determined by the energy density?

I've been trying to figure out how many state functions one needs to fully specify a thermodynamic system. For example, suppose we are given the energy as a function of temperature and volume, i.e. U ...
2
votes
1answer
47 views

Finding the expression for the time it takes for a water tank to be half empty

The problem is to find an expression for the time it takes for a cylindrical water tank is half empty. I am given that the water tank has a diameter of $D_0$ and a hight $H$. The water outlet is ...
0
votes
0answers
57 views

If time somehow went backwards would this violate one of the laws of thermodynamics?

If time somehow went backwards and all the physical events that had occurred in a sequence , would some of the events occurring 'backwards' or in the reverse order violate the principle of entropy or ...
2
votes
1answer
48 views

Effect of breeze on a very hot day [duplicate]

If air temperature is well above body temperature eg air temp of 50C then would a wind make the apparent temperature higher or lower. Clearly the wind would help take away heat due to increasing ...
1
vote
0answers
35 views

mathematical Physics + fluid mechanics, thermodynamics + mass transfer? beginner [closed]

I am completely new to the world of physics and am interested in learning the aforementioned topics. I have previously studied biochemistry, but am fascinated by physics and am interested in ...
1
vote
2answers
39 views

Heating suprecritical water in a closed water tank

How does the pressure of water in a closed tank evolve in the following setting: - closed tank of 2 liters (filled up with water) - water initially at 25°C and pressurized to 3 bars The water is now ...
1
vote
0answers
45 views

Is vortex tube reversible? [closed]

If you inject cold and hot air in outlets of a vortex tube, do you obtain a greater pressure at inlet?
1
vote
0answers
26 views

One question about critical exponents for first order transition free energy [closed]

I've got a problem to calculate critical exponents for theory given by Landau free action: $$ \tag 1 L = L_{0} - \frac{1}{2}(\nabla m)^{2} + atm^{2} + dm^{3} + bm^{4} - hm, $$ where $$ -\infty < ...
0
votes
1answer
56 views

Which laws of physics does this problem break?

One of the problems from the Google Code Jam programming competition, round 2 2015, goes like this: A kiddie pool is a big container in which you can put water, so that small children can play ...
0
votes
2answers
57 views

Definition of an irreversible process

I'm a little bit confused as to why quasi-static process cannot lose energy to friction in order to be reversible. This is how I'm thinking: Suppose you have a container of gas with a piston, and on ...
5
votes
3answers
445 views

How hot can metal get in sunlight? [closed]

I will make some 5mm blackened steel letters for a building. Now, in the sunlight in summer, how hot can they get? EDIT: i want to place some LEDs on the back of the letters. now the question is if ...
0
votes
1answer
42 views

Shape of metal to be heated in consumer microvave oven? [closed]

I tried to use a common 900 W microwave oven melt some alloy with low melting point (138 deg C, eutectic bismut/tin). The metal did not heat up, neither did the metal container, which makes me think ...
1
vote
0answers
24 views

Is it impossible to find the exact analytic form of the molar volume of liquid and gas in phase transition from the van der Waal equations?

I want to find the molar volume $v_g , v_l$ of gas and liquid respectively in the coexistence curve of phase diagram with given temperature when ideal van der Waal gas $$ P = ...
1
vote
1answer
62 views

Why does the temperature of a gas inside a moving container not increase with velocity?

A rectangular (simplified) container with rigid surfaces, has a certain mass of ideal gas within it, and it accelerates in free space, undergoing rectilinear motion. There are no dissipative ...
1
vote
1answer
49 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 ...
0
votes
2answers
53 views

Which materials absorb heat?

Which are the materials that absorb heat? and can i somehow convert that absorbed heat into a different form of energy? I am looking into trying to absorb the wasted heat dissipated by laptops,severs ...
1
vote
1answer
11 views

does the internal energy and enthalpy of the GAS changes in a free expansion process?

when a balloon kept in an evacuated room is punctured and the ideal gas in the balloon goes on to fill the entire room,does the gas perform any work in this expansion, and is there in any change in ...
1
vote
1answer
44 views

Seeking Reference on Transport of Momentum by Diffusion of Mass

I'm looking at continuum mechanics from the perspective of De Groot and Mazur's "Non-Equilibrium Thermodynamics" - the first reference that I've come across that seems to do a good job of bringing ...
0
votes
1answer
41 views

Can gas return back into a sparkling beverage on cooldown?

We all know that if a sparkling beverage (let's say, CocaCola) spends some time outside of the fridge and gets warm, the gas comes out of the liquid, rises the inner pressure and makes the bottle ...
1
vote
0answers
10 views

Increased pressure of Liquid Pitch and Limestone (Bitumen/Asphalt) @ approximately 300 degrees Fahrenheit

If liquid pitch and limestone (20/80 mostly limestone) is pumped (appx. 5 gpm) out of a nozzle that restricts the flow compared to the flow that would be achieved straight out of the pump ( no ...
1
vote
1answer
64 views

Electromagnetic cooling

Heat means stored kinetic energy in matter. Microwave owens and induction heaters works on increasing kinetic energy on matter. Is it possible to make inverse of this heaters like cooler. Can we ...
0
votes
0answers
29 views

What do physicists mean with “classical critical behaviour”?

What do physicists mean with "classical critical behaviour"? As far as I am concerned it should be "power law behaviour" of some quantity close to the critical point but I ask here to be sure.
0
votes
0answers
29 views

Specific heat capacity for constant volume and constant pressure

I have seen in some exercises that the specific heat capacity for constant volume, $c_{vo}$ and the specific heat capacity for constant pressure, $c_{po}$ , where the $o$ indicates that we are ...
2
votes
3answers
58 views

Different materials have different temperatures?

Why do two materials, under the same weather, have different temperatures? I have a small clue about it. For example, iron and wood supposed under the sun's radiation, and if we touch both of them, ...
0
votes
0answers
27 views

Work done by a gas in an expansion [duplicate]

1) Consider a gas expanding quasistatically and reversibly from $V_1$ to $V_2$ at constant temperature. I want to calculate the work done. So by convention work done by a system is a negative quantity ...
0
votes
0answers
12 views

What is the heated added and changes in internal energy? thermodynamics

A piston + cylinder initially contains 2 x 10-3 m3 of helium gas at the pressure of 1.01 x 105 Pa and with a temperature of 60'C. The gas is heated allowed to expand at a constant pressure until its ...
2
votes
2answers
58 views

what is the temperature (and pressure) of the oxygen inside an oxygen bottle?

In the hospital or in a lab, one can see the huge oxygen bottles. A question is, what is the temperature of the oxygen inside the bottle? And what is the pressure inside? We know the critical ...
1
vote
0answers
28 views

Find the time needed to warm the water to a temperature [closed]

An electrical resistence has a power of 1 kW. It is put inside a container that has 10 liters water. The water is in temperature 20C with pressure 1 atm. Find the time to warm the water to the ...
1
vote
1answer
41 views

Find the velocity of the escape of the bullet

A gun has a muzzle 0.8 meters long and with a diameter of 0.006 m. A bullet with mass 0.002 kg is initially 0.01 m away from the end of the muzzle. As a result of a gunshot, the pressure of the gas ...
1
vote
0answers
38 views

Specific heat at constant volume

Me and my friend came across this derivation is some lecture notes of our thermal physics module. We have been trying to calculate the partial differential of the internal energy but cannot get the ...
0
votes
2answers
52 views

derivation qm canonical ensemble

In classical mechanics the canonical ensemble can be derived from the microcanonical ensemble of two systems in weak interaction. Is a similar thing possible in quantum mechanics? Is there any good ...