# Questions tagged [kinetic-theory]

Kinetic theory is part of statistical physics. DO NOT USE this tag for macroscopic kinematics; use the [kinematics] tag instead.

573 questions
Filter by
Sorted by
Tagged with
13 views

### Defining “rate” as absolute difference

My understanding of rate a quantity relates to how that quantity changes with time. In this paper I am reviewing, they defined "bearing rate" of any two ...
59 views

### How can we take pressure of ideal gas be equal to pressure of atmosphere if container is open

I can better put my doubt in form of problem: The temperature of a gas placed in an open container is raised from $27^o$ C to $227^o$ C. The percent of the original amount of the gas expelled from the ...
31 views

### Doubts related to some assumption of kinetic theory

I have doubts related to the kinetic theory of gases which are mostly conceptual which I cannot find in my textbooks. How assumptions the molecules to be perfectly rigid and spherical be good since ...
53 views

### Why collisions with other molecules not taken in account here?

I have few doubts related to this derivation why collisions with other molecules not taken into account since they could also influence the time it takes for one molecule to collide with the wall how ...
12 views

### Volume correction of Van der Waal's equation

A simple derivation of the ideal gas law by assuming all gas molecules to be perfect spheres is as follows: Considering some area of the wall of a container A, the pressure exerted by all molecules ...
26 views

### Why we take time between consecutive collisions on the same wall in derivation of pressure exerted by ideal gas on container by one molecule?

My doubt is why we take time between two consecutive collision $2L/v_{x}$ on the same wall if distance between two parallel face of wall is $L$ instead of the time molecule takes to hit the wall and ...
24 views

### Is there a way to solve this question using instantaneous center method? [closed]

This question is about instantaneous center method of finding velocities. I saw this question on a exam paper, but i think the question may be wrong because i couldn't find a way to get IC(1,3) Or ...
26 views

### Doubt about why to consider partial pressures in calculating vapour pressure [closed]

I am confused as to why the partial pressure is considered while calculating whether a liquid will evaporate in atmosphere or not. But doesn't the reasoning given of molecules colliding also consider ...
30 views

### Confusion with degrees of freedom [closed]

I am facing a lot of confusion regarding the degrees of freedom of various molecules. I want to know some facts with certainty. I will talk about what I have read, please correct me if I am wrong. I ...
40 views

### Distribution of molecular speeds (kinetic theory of gases)

What is the physical significance of the $N(v)$? I know that the product $N(v)\ dv$ gives the number of molecules in a given speed range of $v$ to $v+dv$ but is there any meaning of $N(v)$ itself? ...
85 views

### What is the theoretical justification for the Law of Equipartition of Energy?

What is the theoretical justification for the Law of Equipartition of Energy? Why are equal energies distributed in each degree of freedom even though sometimes they are completely different (like ...
42 views

### Divergence theorem & Kinetic model of plasmas

In one section in my plasma physics notes (see below) on the Vlasov equation, 6D phase space & the kinetic model for plasma, I can't quite understand how (via Gauss's divergence theorem) this ...
242 views

### Is it possible for two gases to have different internal energy but equal pressure and temperature?

Apparent contradiction between specific heat ( i.e internal energy, in this case) and average kinetic energy (i.e temp). For ex- if i take two gases [He] and [Xe] then xenon have more specific heat ...
54 views

### Good reference for undergraduate introduction to the Master equation and Fokker-Planck equations

So I have a background in statistics and differential equations, but not much physics at all. But I am working on a project relating to stochastic differential equations and Markov processes. I was ...
45 views

### How many Degrees of Freedom do Linear Triatomic Gas Molecules Have and Why?

I read this in one of my textbooks that stated Linear Triatomic Gas Molecules like CO2, HCN, CS2 in which all the atoms are linear, the total number of degrees of freedom are Nf = NT + NR + NV where ...
33 views

### Thermodynamic function describing an ensemble [closed]

Consider an ensemble of thermodynamic systems each of which is characterized by the same number of particles, pressure and temperature. The thermodynamic function describing the ensemble is (a) ...
40 views

### Boltzmann equation: how to estimate the relaxation time?

I am looking for qualitative/general explanations or references. A famous approximation of the full integro-differential Boltzmann equation is the so-called "relaxation time approximation", ...
40 views

### Kinetic average energy of $N$ particles [closed]

Really quick doubt: we know that $\overline{E_c}=\frac32 kT$ where $k=1.38\cdot 10^{-23}\frac{J}{K\cdot particles}$ but particles isn't really a unit, I know, but imagine they ask me about $N$ ...
32 views

### Deriving Bernoulli's equation with the kinetic gas theory: Missing 1/2 factor

Inspired by Eugene Khutoryansky video about Bernoullis law (https://www.youtube.com/watch?v=TcMgkU3pFBY), I decided to put the thoughts and ideas from her video into mathematical terms. My derivation ...
69 views

58 views

### For a gas in an open vessel, should the volume of gas be the volume of whole universe?

In the ideal gas equation $PV=nRT$, $V$ is defined as free space available to the gas. In an open vessel in which temperature is maintained constant, shouldn't the volume $V$ of the gas be the volume ...
17 views

### How do we explain No change in Entropy in an Adiabatic Quasi-Static Expansion from the perspective of Boltzman's Idea of Entropy?

I understand from the formula of Clausius idea of Entropy that the change in entropy in an adiabatic quasi-static process is zero. I do not understand, how we can explain the same idea from the ...
105 views

### What is the kinetic energy of one molecule of a polyatomic gas?

According to Kinetic theory, the kinetic energy of one molecule of gas is 3/2kT. Is this true for diatomic and polyatomic gases as well? I've read that a diatomic gas has 5 degrees of freedom (3 ...
28 views

### A question on mean free path of gases in a container [closed]

Two identical containers kept at the same temperature carry the same gas with different molecular mean free paths l1 and l2. the gas from the first container is completely transferred in to the ...
71 views

### Why do we use RMS speed rather than just taking the average of absolute value of the speeds?

I get that negative values to cancel positive values, and that is the reason why we don't do a direct average. So why don't we just use the absolute value mean of the speed? If I have one gas particle ...
26 views

### Does the Maxwell Boltzmann velocity distribution deal with the velocity of centre of mass

Very basic question here. Does the Maxwell Boltzmann velocity distribution deal with the speed of the centre of masses of multiatomic( like Nitrogen ,oxygen) species or with the exact speeds of atoms?...
168 views

### Why is the temperature of a gas proportional to the average kinetic energy of its particles?

I'm studying the kinetic theory of gases I managed to derive that pressure is inversely proportional to volume and directly proportional to the average kinetic energy of the gas particles. Similarly, ...
28 views

### How does one physically achieve a constant state variable process in thermodynamics?

Recently, I was studying about the various different paths which we can go through in thermodynamics, and, I wish to ask how exactly we can achieve a process such as a constant temperature or ...
38 views

### What happens to Atom KE when it's supressed by other forces?

Assume fallowing situation: Atom 1 travels in direction of Atom 2 with velocity (kinetic energy) vy. As Atom 1 gets closer to Atom 2, the Atom 2 repealing forces have more impact on Atom 1. At some ...
48 views

### Atom kinetic energy transfer

So according to physics laws, energy can't be created or destroyed but transformed from one form to another. But what happens when an atom flows with certain velocity and is stopped by other atom's ...
69 views

### Why do atoms move?

According to Kinetic theory of matter: "All matter is made up of atoms and molecules that are constantly moving". But why? What is the deep explanation for the movement (translate, rotation ...
107 views

### Maxwell-Boltzmann distribution in conductors?

In the kinetic theory of gases, the Maxwell-Boltzmann distribution is commonly used to describe the velocity distribution of gas molecules. My question is to what extent (if at all) can such a ...
172 views

### Looking for an alternate derivation of collision frequency of ideal gas molecules with the container walls

I've learnt how to calculate the collision frequency of ideal gas molecules with the walls of container using Maxwell Boltzmann distribution given as $$f=\frac{1}{4} n\langle v\rangle$$ However I was ...
45 views

### Why $dE + dW = C_pdT$?

$dE$ is Internal Energy $dW$ is Work Done $C_p =$ Specific heat at Constant Pressure In Mayer's Reaction, They have given the relation $dE + dW = C_p.dT$ But I don't know how they have Derived this ...
34 views

### Why does thermal conductivity decrease from solids to gases?

I am learning in my heat transfer class that the thermal conductivity decreases from solids to liquids to gases i.e. $$K_{solid} > K_{liquid}>K_{gas}$$ The reason cited is that (based on my ...
81 views

### Interpretation of kinetic energy and temperature in thermodynamics

Consider the question above. Till now I have interpreted kinetic energy as a consequence of temperature in thermodynamics, i.e., the kinetic energy of a gas is directly proportional to its temperature....
25 views

### Looking for a way to derive the velocity distribution along x axis given the distribution for a general velocity

Without recourse to statistical mechanics my book derives the well known Maxwell Boltzmann velocity distribution which is: dN(v)=N\left(\frac{m}{2 \pi k T}\right)^{3 / 2} e^{-m v^{2} / 2 k T} 4 \pi ...
63 views

### Kinetic Equation of Gas: Why is $T$ not the time of impact?

so i just learnt about about the derivation of Kinetic Gas Equation! In that derivation, and i have a question which i am trying to find the answer for but i can't find it anywhere on the internet! In ...
Question is simple: I was asked to find the average speed of oxygen gas molecules at $T = 300^o K$. I thought the answer was simple too, as simple as plugging in the equation for $v_{avg}$ which is ...