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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How does gas friction emerge?

The fluid parcel model states that a gas can be modelled as the sum of infinitesimal small parcels. According to this model, the friction of a gas with a solid surface (e.g. the wall of a pipe) ...
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How Pressure Change by Time in Closed Box?

Imagine that you have 1 cubic meter metal box. And there is two holes. Two of them has 20 mm diameter. One of them connected to air-compressor that give constantly pressure inside of cube.Let say 5 ...
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Deriving Ideal Gas law from Hamiltonian Mechanics

I just don't understand the explanation in Wikipedia. Is there a nice & elegant way of arriving at the Ideal Gas Law from Hamilton's Equations?
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Water compressibility and pressure

I am so sorry if I am missing something, but for some reason I am very confused on how water can have pressure but not be compressible. If pressure is created by individual molecules bumping into the ...
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224 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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8 views

Modeling stilts with equations

I'm trying to make a set of stilts 20 ft in the air that someone could wear to run/jog with, but I was advised that I should first start by modeling the system (user + environment + stilts) in the ...
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Boyle's Law-$ PV= nRT.$ What equation should be used to find pressure if n is not constant, like in an elastic system?

When air is added to an elastic system, like a balloon, the volume and pressure change. Would use Boyle's Law- $PV=nRT,$ but n does not remain constant in this situation. Known: $V_1$ is at ...
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Is there a temperature drop at the rotor plane of a wind turbine?

A wind turbine rotor produces power from the torque generated by the rotor blades. This torque arises from forces on blade elements which in turn are the consequence of pressure differences on each ...
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Statistical mechanics - average particle energy, average kinetic energy

I'm looking at derivations for average particle energy giving $E=kT$: http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/bolapp.html And average particle kinetic energy giving $K_E=\dfrac{3}{2}kT$: ...
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Momentum change in collisions (Drude model)

A particle suffers elastic collisions with scattering centres with a probability of collision per unit time $\lambda$. After a collision the particle is in a direction characterized by a solid ...
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Average Rate of Evaporation of Water

Consider a container of volume $V$ and cross sectional area (exposed to another fluid, say air) $SA$. The container is at constant temperature $T$, and contains $N$ molecules of water, where $N$ is ...
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Physical reason why Prandtl number is order unity for gases?

Is there a physical reason behind the fact that for gases the thermal diffusivity is on the same order of magnitude as kinematic viscosity (and as such a Prandtl number of order unity) and if so what ...
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Conceptual problem on Maxwell's velocity distribution law

I already read about Maxwell's velocity distribution law for gas molecule. And the expression for that distribution is following dnc=4πnA^3e^(-bc^2)c^2dc Now if we assume that the molecules have no ...
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1answer
218 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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22 views

probability of striking the circular ring by gas molecules

In kinetic theory we use probabilistic case to derive pressure, no. Of molecules having speed c to c+dc or in such cases.and to derive such equations we introduce a term called "SOLID ANGLE" I come ...
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21 views

Interial Momentium Question

I had a question for my Physics 101 class and was wondering if anyone could share some insights. The question was stated as follows. A pottery wheel of radius 0.5 m and mass 15 kg rotates ...
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Why does the temperature of the gas in a container moving with constant velocity not change?

Systematic changes do not affect thermodynamic equilibrium. What does this mean? And what kind of systematic changes are allowed? The container with gas is stationary till some time then it's ...
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196 views

Why does Triple point exist?

In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium. Is ...
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Is the pressure-gradient force an entropic force?

A gas flows from an area of high pressure to an area of low pressure when there are no other forces preventing it. From a macrosopic perspective you have to infer that an underlying force is ...
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Gas diffusion through a flat plate boundary layer

Set-up Suppose we have a flat plate with a flow of gas parallel to the plate. The flow creates a boundary layer on the surface of the plate. Now, the gas is carrying a reactive species, which is ...
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46 views

Difference between semi-classical Maxwell Boltzmann Statistics and Boson Statistics

Since semi-classical MB assumes the indistinguishability of particles and Boson Einstein statistics similarly treats degenerate states as indistinguishable states. What is their difference when ...
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1answer
32 views

What is the relation of particle velocity, temperature, and reaction activation energy

So, this curiosity has arisen for a fun project I thought I'd tackle, where I'm attempting create a crude simulation of an internal combustion cylinder. I wanted to explore the particle level ...
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Can wind be defined as momentum/mass of air molecules?

In the past I thought a breeze of wind was "made" from a large amount of air molecules going all the same direction in the same speed. But it's not like that, actually this voted answer, this site, ...
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relationship between pressure and thermal conductivity

Using a kinetic model for gases, is it possible to derive a relationship between pressure and thermal conductivity? From what I have read, I thought pressure was independent of thermal conductivity? ...
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Collision: How can I calculate the effect of an object below 1 kg on another heavier object after colliding [closed]

I have a question on collision: 1. A light object (0.75 kg) is travel in velocity V m/s. 2. This object collide into another object which is about 9.5 times of its weight. 3. So, the question is ...
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Van der Waals equation

In the Van der Waals equation, $$\left(p+\frac{a'}{v^2}\right)(v-b')= kT$$ The excluded volume b is not just equal to the volume occupied by the solid, finite-sized particles, but actually four ...
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Diffusion (2 species) versus advection (1 species)

Why do we see diffusion with 2 species but advection with a single species if both cases involve molecules spreading to increase entropy? To take a physical example: Let's say I have a box with two ...
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isothermal compression of water and definition of temperature

During isothermal compression of water vapour (below critical temperature), the pressure increases initially, and then remains constant up to certain point, and then steeply increases with small ...
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How does evaporation affect the temperature of the air?

A wet object or a volume of water will decrease in temperature due to the effect of evaporation. We understand this to be because of the molecular kinetics, where the faster water molecules escape ...
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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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Classical Quantum or Relativistic? [closed]

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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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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72 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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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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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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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
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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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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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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 ...
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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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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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5answers
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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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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
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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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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
59 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
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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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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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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 ...