Kinetic theory is part of statistical physics. DO NOT USE THIS TAG for macroscopic kinematics. In this case, use the tag [tag:kinematics] instead.

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Classical Quantum or Relativistic?

An ensemble contains free electrons at 10^3 electrons per m^3 at 10^7 K. What can this ensemble be treated as: a Classical Quantum or Relativistic gas or in some overlapping domain?
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+50

Why do some substances undergo sublimation while others do not?

This question is indeed lengthy...but please go through the question at least. From the study of kinetic theory I know that for intuitive answers we can associate the states (liquid, solid,gas) with ...
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0answers
9 views

What is the velocity of a given ion in aqeous solution?

I have seen many calculations of the velocity of X element in air at a given temperature. It has a nice closed equation: v(O2) = √ (3kT/m) However I am unsure where to look for the velocity of ions ...
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3answers
57 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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3answers
2k views

Why do moving particles emit thermal radiation?

While answering another question about heat in an atom, the discussion in the comments led to the question of how heat is related to thermal radiation picked up by infrared cameras. The answer is that ...
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1answer
191 views

Flow rate of gas down a pipe at low pressures

I'm trying to understand an 'approximate derivation' of the flow rate of gas down a pipe at low pressure from my book (an example problem). It uses the result that the flux of a gas is given by ...
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1answer
34 views

Dependence of average speed of molecules of gaseous mixture

We know that the average speed of gases in a single gas chamber is given by $\sqrt{8RT/\pi M}$ where R is universal gas constant,T is temperature,M is molar mass of gas. But what if we mix two gases ...
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1answer
48 views

Kinetic theory of physics [closed]

$$E = (3/2) kT$$ For average kinetic energy of a molecule gas.The constant $k$ does not depend on the type of molecule. Can this result be true for both hydrogen and chlorine?
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1answer
37 views

Derivation of the diffusion coefficient?

The diffusion coefficient relates the particle flux $J$ to the gradient in the number density (of the 'labelled' particles) $\frac{\partial \bar n}{\partial z}$ such that; $$J=-D \frac{\partial \bar ...
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2answers
162 views

What is the correct relativistic distribution function?

General Statement and Questions I am trying to figure out the proper way to model a velocity/momentum distribution function that is correct in the relativistic limit. I would like to determine/know ...
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1answer
32 views

How does potential energy relate to kinetic energy on a rollercoaster?

This is appearantly how the potential and kinetic energy are in the different positions of the rollercoaster, if I am not mistaking. However I don't understand why the total energy is energy and ...
6
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2answers
137 views

Why does warm water sink?

It is well known that water at 4C is denser than water at 0C. This is the usual explanation for why a body of water freezes from the surface (also it's because ice is even less dense, but that's ...
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0answers
40 views

Mean free path in 2d?

Let us say we have a collection of $n$ stationary balls per square meter each of diameter $d$ and we roll an identical ball between them. Then what is the free mean path of this ball? My ...
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2answers
414 views

Momentum change in collisions (Drude model)

A particle suffers elastic collisions with scattering centers with a probability of collision per unit time $\lambda$. After a collision the particle is in a direction caracterized by a solid angle ...
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5answers
91 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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1answer
22 views

In kinetic theory when can we ignore forces?

Let us say I have a body of gas for which there is an external force $F$ (which could be say gravity) acting on the particles. What conditions should $F$ satisfy before I can assume that the effect of ...
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1answer
25 views

Dilemma on work done by gas in isothermal contraction

Consider an ideal gas inside a cylinder undergoing reversible isothermal contraction. Now if we consider the forces acting on the gas inside the cylinder the force acting is $P_{ext}\cdot A$, however ...
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3answers
650 views

Derivation of viscosity using basic kinetic theory?

This question has been asked in part before in the question Kinetic theory derivation of viscosity of a gas although the given accepted answer does not give the required detail for the part of the ...
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1answer
53 views

Why take RMS velocity?

Why do we consider RMS speed of gases in various calculations? For example, I have to find the time for two successive collisions to occur for a hydrogen molecule.I get the answer if i calculate using ...
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1answer
38 views

Liquid phase is a highly compressed gaseous phase

$\mathbf{Q:}$ While teaching "Real Gases", my professor remarked last day that "Liquid phase is a highly compressed gaseous phase." But he did not explain the reason behind it and left it as food for ...
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0answers
24 views

Comparing relative velocities and kinetic energy

If object one is moving $0\frac{m}{s}$ relative to the Earth and object two is moving $1\frac{m}{s}$ and they both have $1kg$ of mass, then object one has no kinetic translational energy (relative to ...
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4answers
209 views

Why the round trip instead collision time?

From Newton's second law, the $\Delta t$ is defined as the collision time, but why in this case, it can be assumed to be the value of time between successive collisions on 1 wall? If I have an ...
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0answers
11 views

Diffusion coefficent for a mixtures gases?

In the Pauli Lectures on physics volume 3 it is stated that for gas mixtures the diffusion coefficient is given by: $$D=a'' \frac{1}{n} (n_1 \bar u_1 l_1 + n_2 \bar u_2 l_2)$$ Where $n=n_1+n_2$. How ...
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1answer
695 views

Kinetic theory derivation of viscosity of a gas

Encountering a lot of issues trying to understand this. The basic idea of the derivation I'm using is as follows (the image here may help): I'm going to write $\langle u_x\rangle$ as the general ...
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3answers
327 views

Liouville's Theorem and Boltzmann equation for plasma

The Boltzmann equation for a plasma can be thought of as coming from a continuity equation in the 6 dimensional phase space of the plasma with coordinates $\left\{x,y,z,v_x,v_y,v_z \right\}$. So ...
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0answers
29 views

Boltzman equation for a collisionless medium?

In the derivation of the Boltzmann equation (link to Wikipedia) for a collisionless gas it is assumed that: $$f(\vec r+\frac{\vec p}{m} \Delta t, \vec P + \vec F \Delta t, t + \delta t)=f(\vec r, ...
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1answer
36 views

Do liquids creep from cold to hot like gases?

Consider the U-tube water experiment below with the left red block at 10C and the right red block at 90C. I think the right level will become about 3% higher than the left level simply because hotter ...
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1answer
42 views

What is a good software for Ideal Gas simulation?

I am looking for a software that simulates the microscopic behavior of an ideal gas, something like this: http://www.youtube.com/watch?v=tEFHkcx2cz0 (unfortunately this program is not openly ...
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3answers
61 views

If Gravity acts on the particles in the gas, why don't they accumulate on the lower surface and fall down?

A quantity of gas is enclosed in a metal cylinder fitted with a piston. There are very many gas molecules.The cylinder walls are thermally conducting. Now, the question...
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0answers
102 views

Le Sage's Theory of Gravitation, is “drag” the only reason why this theory fails? [closed]

Le Sage's Theory of Gravitation was originally proposed allready 1690 by Nicolas Fatio, and has ever since been studied by remarkable scientists; Leonhard Eluer once remarked that it was "infinitely ...
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0answers
45 views

Is there a theoretical maximum speed for wind?

What we call wind is actually molecules moving into an area of lower particle density due to their thermal motion. A lower particle density offers less collisions (resistance), so more molecules move ...
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5answers
2k views

0 Kelvin body moving

As many books say: Temperature is (proportional, almost, etc...) average kinetic energy of particles. My question is this. "Suppose there is a body somewhere in empty space which moves at ...
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0answers
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Confusion about radioactivity

The following question is from General Problems on Physics by I.E Irodov 6.220. Find the decay constant and the mean lifetime of $^{55}\operatorname{Co}$ radionuclide if its activity is known to ...
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0answers
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How much do we know about the characteristic time for electron-ion recombination for a dense plasma?

As mentioned, how much do we know about the characteristic time for electron-ion recombination for a dense (noble gas) plasma (i.e. density of electrons at $\approx 10^{21} \textrm{cm}^{-3}$) at ...
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1answer
56 views

Zero Energy State of a Mechanical System? [closed]

Would a mechanical system in a particular frame (when I say mechanical I mean pulleys, elastic strings, etc.) that has no potential energy (loaded springs, pulled back elastic, hanging weights, etc.) ...
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2answers
96 views

Derivation of ideal gas law

I looked up on the ideal gas law which our high school textbook derives with the empirical Combined Gas Law. However, the textbook did give a good explanation for this equation $$pV = ...
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0answers
68 views

Diamonds are not forever?

It is frequently stated that although graphite is the more stable allotrope of carbon at STP, the activation energy of the diamond-to-graphite transformation is so high that our diamonds will never ...
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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
38 views

alternative derivation of Einstein relation

Is there a derivation of the Einstein–Smoluchowski relation without the assumption of the Boltzmann distribution? Every time I see a derivation, it always assumes the Boltzmann distribution, such as ...
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0answers
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If I want to sample rate constants of chemical reactions, what the distribution will be appropriate? [closed]

For example, I have a (chemical) reaction systems, I want to sample the parameter space. What will be the best and validated distribution for sampling? And why? Thanks!
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2answers
98 views

Specific heat capacity and temperature, 0 K?

I've found similar threads like this, but with no clear answer. I understand that the specific heat capacity of a substance increases with temperature, because the vibrational nodes and rotational ...
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0answers
36 views

Equation of Motion from Vlasov Equation

From the Vlasov equation $$\frac{\partial f}{\partial t} + \vec{v} \cdot \nabla f + \vec{a} \cdot \frac{\partial f}{\partial \vec{p}} = 0$$ we can obtain the momentum transport equation by ...
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1answer
53 views

Can Kinetic Theory obtain fluids behavior?

My understanding is that it can't. But when presenting it here I received comments that contradict this. So, as suggested, I am asking the question to be able to receive concrete approaches on this ...
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0answers
267 views

Simple: What do these ballistic impact numbers represent?

I bought physics for game programmers, found here, today to study ballistic impact, but I'm confused as to where a few numbers are coming from. I'm basically looking to understand what the values ...
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1answer
942 views

Finding the approximate distance between molecules in a gas

I have a problem to understand why the below derivation can be used to find the distance between molecules: This example is an approximation. We are supposed to find the average distance between the ...
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0answers
36 views

Gaussian acceleration of magnetic/nonmagnetic balls

https://youtu.be/CoHGGZfERE0?t=19s In this video, 19 seconds in, a nonmagnetic ball (henceforth just called a ball) is launched slowly at a static magnetic ball butted up against another static ball. ...
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0answers
49 views

Integral over a surface in kinetic theory [closed]

I am working with some kinetic theory. I have the distribution function $\Psi (\vec{r},\vec{p},t)$, Where $\vec{r}$ is the radius vector, $\vec{p}$ is the unit vector of orientation, and $t$ is the ...
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3answers
127 views

Why is there no change in speed of a charged particle in a uniform perpendicular magnetic field? [duplicate]

When the initial velocity is perpendicular to the magnetic field, the force acting on the charged particle F = qvBsin(theta) ...
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1answer
32 views

How are smoke cells an example of Brownian motion?

I don't get how smoke cells are an example of Brownian motion.
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1answer
120 views

How to explain the Venturi effect with Kinetic Theory?

From a macroscopic perspective a fluid flowing through a pipe gets accelerated when the pipe's cross section gets narrower. According to $F= ma$ a force must be present to do this. This force is ...