Tagged Questions

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

52 views

46 views

If a flywheel is spinning at say 1,000 rpm, would an input of 500 rpm would actually slow it down? [closed]

When a flywheel is stationery, an input of 500 rpm would translate to less than 500 rpm in the flywheel considering entropy, but what happens if the flywheel is already running at 1000 rpm, wouldn't ...
61 views

What VOLUME does exactly the $V$ term in ideal gas equation represent?

According to kinetic theory of gases 'the actual volume occupied by the gas molecules are negligible in comparison to the volume of the container.' I believe that this assumption is significant ...
95 views

Relation between master, Fokker-Planck, Langevin, Kramers-Moyal and Boltzmann equations

I'm looking for the relation between four important equations which we study in stochastic processes in physics. These equations include Master, Fokker-Planck, Langevin, Kramers-Moyal and Boltzmann. ...
69 views

How much faster are airmolecules going when the temperature raise from 15 to 25 degrees C?

As far as I know the temperature of the air depends on how fast the airmolecules are moving. But what is the increase of speed (in km/h) of those air molecules?
82 views

Maxwell velocity distribution, in 1D or otherwise

I learned from my textbook that Maxwell's velocity distribution gives: $$v_{rms} =\sqrt{\frac{3kT}{m}}$$ $$v_{avg} = \sqrt{\frac{8kT}{\pi m}}$$ Presumably this is for a three dimensions. This confuses ...
38 views

Why only $x$-component of gas particle changes when it strikes with wall perpendicular to $x$-axis elastically?

In my book ''Ncert Class 12" It is written We begin by considering the collision of one molecule with one of the walls of the container, oriented with a unit normal vector pointing out of the ...
23 views

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) ...
69 views

How does pressure change over time in an open box?

Imagine that you have a 1 cubic meter metal box with two 20 mm diameter holes. One of them is connected to an air-compressor that constantly pressurizes the inside of cube. Let's say 5 atm. The other ...
70 views

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?
85 views

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 ...
9 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 ...
20 views

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 ...
32 views

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 $K_E=\dfrac{3}{2}kT$: ...
34 views

When a liquid solidifies why does internal energy fall? [closed]

Is it because the potential energy falls or is it because the kinetic energy falls .
16 views

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 ...
37 views

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 ...
53 views

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 ...
35 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 ...
24 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 ...
38 views

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 given ...
67 views

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 ...
106 views

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 ...
38 views

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 ...
60 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 ...
38 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 ...
63 views

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, ...
248 views

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? ...
14 views

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 ...
328 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 the ...
59 views

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 ...
37 views

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 ...
71 views

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 ...
30 views

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?
28 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 ...
78 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?
366 views

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 ...
37 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 ...
$$E = (3/2) kT$$ 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?
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 n}...