Questions tagged [ideal-gas]

A gas that behaves as randomly moving, non-interacting molecules. This allows a simplified equation of state.

179 questions with no upvoted or accepted answers
Filter by
Sorted by
Tagged with
5
votes
1answer
127 views

Stagnant Air Deep Inside Vintage Mines

This is really a question more about mining ventilation than true "physics." I occasionally explore a southwest desert mine, but am aware of the hazards - typically passing over half a dozen vintage ...
4
votes
0answers
91 views

Ideal gas equation vs Kinetic theory equation

From the ideal gas equation: $PV = NkT$, since Pressure times Volume = Energy, my understanding is that the total (internal) energy of $N$ molecules of a gas $= NkT$. However from the kinetic theory ...
3
votes
0answers
84 views

Question about a hand-waving estimation done by Landau

I was reading the book written by Landau on statistical mechanics (Statistical Physics I 3rd Ed). In §1 there is a footnote that Landau wants to illustrate how accurate a statistical average can be ...
3
votes
0answers
481 views

Effusion Flux according to Kinetic Theory

We know from Kinetic Theory that, for a dilute monoatomic gas, particle average velocity perpendicular to a wall of the container is given by: $$ \begin{align} \langle v \rangle _s &= \frac{\...
3
votes
2answers
332 views

How do we find force to derive $pV=Nmv^2$?

Since momentum is not changing in time t , but instantaneously in very small time at wall B. Why do we write $F=\frac{2mv}{t}$? Where $t$ is (twice the distance AB)/ velocity. Why don't we take the ...
3
votes
0answers
138 views

Is it possible to have a line rather than a point where the three states of a substance can exist?

Most of us are familiar with state diagrams that define which of the three states a substance will take given the pressure and temperature. And that some substances, such as water for example, exhibit ...
3
votes
0answers
68 views

Can I always assume that a vapour pressure over a liquid is ideal?

Can I assume that the vapour of a subject over its liquid is ideal-ish? I'm thinking that if the vapour pressure is low the subject in question wont interact with itself, but it doesn't necessarily ...
3
votes
0answers
177 views

error propagation and collision in ideal gas

When dealing with gas, a statistical approach is needed because For N particles, you have to solve 6N equations which cant be done analytically. To know our time step for numerical solving, you can ...
2
votes
1answer
34 views

Deformation of a sphere

I am currently building a computational model for a simulation of a rover landing on the surface of mars. As part of the assignment I need to model airbags being used to cushion the fall. (Assuming ...
2
votes
0answers
16 views

Evaporation of a gravitationally-bound spherical cloud of a warm ideal gas in a vacuum

It seems that for any gravitationally bound system with a very large number of atoms/particles, there will always be some particles that manage to achieve escape speed and ultimately leave the cloud. ...
2
votes
0answers
52 views

Confused about summing over the velocity squared term

Consider a cubical box, L on each side. The box contains N molecules of ideal gas, each of mass m. All collisions are elastic. The force exerted by one molecule when it collides with a wall of ...
2
votes
0answers
46 views

Boltzmann transport equation for granular gases

I am researching about granular gases and their collisions, and have come across this Boltzmann transport equation: $$\frac { \partial f ( v ) } { \partial t } = \iint d u _ { 1 } d u _ { 2 } f \left( ...
2
votes
3answers
2k views

Ideal gas and moveable pistons

Suppose there is an ideal, monatomic gas contained in a cylinder with a moveable piston and you bring that system (system = gas only) through some process. If that process changes the volume (or ...
2
votes
0answers
120 views

Weird and unintuitive results from thermodynamics/hydrostatics for an isothermal atmosphere and possible explanation(?)

It is known from hydrostatics that for a fluid in equilibrium in a gravitational field, $$\frac{dP}{dz} = -ρg$$ Let us from now on suppose the atmosphere is isothermal and has temperature $T$. We ...
2
votes
1answer
158 views

Confusion while deriving kinetic-molecular theory of gases

How many of the molecules will collide within a given area A of the wall normal to the x-direction in some fixed time interval Δt ? On average half the molecules have a positive x-...
2
votes
0answers
213 views

Feynman Lectures I 40: Is the homogeneity of the Maxwell-Boltzmann distribution a result of, or a pre-requisite for its derivation?

I refer to hand-waving a lot in this post. That is not to say that it was in appropriate. Feynman pretty much said at the outset that his treatment of thermal physics was going to be less than ...
2
votes
0answers
227 views

How was the ideal gas equation derived?

How did people come up with the formula: $$PV = nRT = k_BT \qquad$$? I see two possible ways: 1.) We did some measurements and defined $$kB:=\frac{PV}{T},$$ remarking that $\frac{PV}{T}$ is ...
2
votes
0answers
2k views

Limitations of the ideal gas law: When does it fail?

Motivation I ask this question precisely because I am looking for a fundamental, quantitative explanation of the limitations of the ideal gas law and when it should not be used. Note, I have found ...
2
votes
0answers
39 views

Ratio of Stagnation to Normal Flow Properties in Incompressible Flows

I know in compressible flows the ratio of stagnation to normal flow variables is a function of the Mach number and usually the specific heat ratio. Does this ratio mean anything for incompressible ...
2
votes
3answers
72 views

When deriving pressure, why do we take rebound time to be travelling time?

The derivation of the ideal gas law runs along the following lines. Imagining a container filled with some particles, by definition: $P = F/A$ $F = dp/dt$ $F_{avg} = \Delta P/ \Delta t$ If we ...
2
votes
0answers
69 views

How is convection possible in fluids, in the absence of a contact surface for any buoyant force?

I don't understand why liquids and gases are acted upon by a buoyant force. In a solid immersed on some fluid medium, the pressure pressure difference caused by gravity exerts a force on the surface ...
2
votes
1answer
833 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 $\...
2
votes
0answers
429 views

Simple gas in cylinder modeling

I want to do a simple (physically plausible but not physically accurate) simulation of a gas in a cylinder as it works on or is worked on by a piston. Wikipedia gives a good example of an adiabatic ...
2
votes
0answers
148 views

Recombination time for ionized atoms in a low pressure gas?

I am looking into some new physics and had the following question come up: You have a neutral gas of let's say, CO atoms at 1 nanoTorr. An electron(s) comes passing through the gas ionizing only 1% ...
2
votes
0answers
282 views

Centrifugal Compressor Flow Rate

For a centrifugal compressor, as found in most turbochargers on internal combustion engines, is there a noticeable change in flow rate versus a naturally aspirated flow rate? In other words, does the ...
1
vote
0answers
21 views

Entropy of mixing canonical ensemble

I am solving a problem that analyzes a classical ideal monoatomic gas. After determining the partition function, free energy and entropy, it asks me to analyze the variation of entropy if I had a wall ...
1
vote
0answers
18 views

What is the single particle translational partition function for a single gas atom in unknown volume?

In the standard expression for the ideal gas translational partition function, we have a V for the volume. How do we compute this partition function for a gas when the volume is unknown, like the ...
1
vote
1answer
33 views

What is contribution of Rotational Kinetic energy in temperature of gas according to kinetic theory of gasses?

We know that, for one molecule of ideal gas, $U = \text{Kinetic energy} = \frac{f}{2}RT$ where $f$ is the number of degrees of freedom, $R$ is the gas constant and $T$ is the absolute temperature. So ...
1
vote
0answers
20 views

Duration of adiabatic expansion

I have a problem in which an adiabatic expansion occurs in a vertical piston and ideal gas system. There is a piston that is being held down, and then when it is released, the gas expands in such way ...
1
vote
0answers
28 views

Does hero's engine have an upper limit for the rotational speed under ideal conditions?

This is a simple hero's engine. The source of the gas and the rotating part is seperated by a frictionless bearing. So only the upper part rotates. My question is this: Given ideal conditions ( no ...
1
vote
0answers
34 views

Why Pascal's law is applicable for ideal gases?

Pascal's law is about incompressible fluids. But ideal gases are compressible. Still, Pascal's law is applicable to ideal gases as far as I know (might be wrong). Why is it applicable for ideal gases?
1
vote
0answers
19 views

Raoult's Law and Boiling Point Elevation

Raoult's Law states that vapor pressure decreases when a non-volatile solute is present. Boiling point is when vapor pressure = ambient pressure. Since vapor pressure is less, shouldn't the energy ...
1
vote
1answer
20 views

How does a piezoelectric oscillating cantilever fan operate in different gases?

A piezoelectric oscillating cantilever is a structure composed of a piezoelectric material with a flexible blade attached to it. While alternating voltage is applied over the material, it starts ...
1
vote
1answer
38 views

Confused with a simple ideal gas model

For an ideal gas of two-component ($A+B$) mixture at a temperature $T$, which expression is correct? $$p_T=p_A+p_B \tag{1}$$ or $$\rho_T=\rho_A+\rho_B, \tag{2}$$ where $p_T$ and $\rho_T$ are the total ...
1
vote
0answers
16 views

Chamber with semi permeable membrane

Consider two cases in a chamber in which gases are filled on both sides of a partition which acts a semi permeable membrane : 1.Hydrogen is filled on one side of the partition and it can move through ...
1
vote
0answers
89 views

Is the entropy change due to particle insertion/deletion the same as increasing/decreasing the volume (or pressure) for an ideal gas?

Background: Consider a pure monatomic ideal gas within a closed system undergoing a reversible, isothermal compression/expansion. The fundamental thermodynamic relation is $$d U = T d S - P d V + \mu ...
1
vote
2answers
70 views

What does the work term mean when analyzing a ideal gas and spring system?

This problem has been bugging me for a long time now. It states that given an insulated cylinder which contains a spring and an ideal gas, you must calculate the work required to compress the gas, ...
1
vote
1answer
58 views

Negative value of $dq/dT$ in a polytropic process

Consider a reversible polytropic process :$$PV^x=K$$ where $K$ is a constant. We can easily derive , By differentiating this and using the gas laws, that for such a process: $$PdV=\frac {(nRdT)}{(1-x)}...
1
vote
1answer
45 views

When the volume of a container of gases is decreased, does the Root mean square speed increase or decrease?

I'm a High School student learning the kinetic theory of gases, and this is something I'm a bit confused about. So say there's a container covered with a piston. When you lower the piston and ...
1
vote
1answer
57 views

Two versions of Diffusion coefficient

I found two versions of the Diffusion coefficient, first: $$D=\frac{\pi \lambda }{8}\overline{c}$$ Where $ \overline{c}$ ist the particles mean thermal velocity and $\lambda$ the particles mean free ...
1
vote
1answer
114 views

Can a gas molecule theoretically have zero velocity?

According to Maxwell's speed distribution law gas molecule can have speed which lies between zero to infinity. But in the graph of the distribution curve it seems to touch zero velocity. So can a gas ...
1
vote
3answers
57 views

Relation between volume of a room and temperature inside

I don't know whether it is based on some people's assumptions or it is a fact that the smaller the room, the hotter it is (say, during summer), considering the heat is only supplied from outside the ...
1
vote
1answer
31 views

Weight exerted on scale by balloon filled with ideal gas

I want to compute the weight of a spherical balloon (with radius $r$) in vacuum filled with ideal gas. The balloon is laying on a scale. Using the barometric formula $$ P(h)=P(h_0) e^{-\alpha(h-h_0)},$...
1
vote
1answer
71 views

How much power is needed to keep ideal gas in a fix volume?

I was playing with the idea of entropy and an interesting thought came out. Imagine a physical cube with side $a$. Inside the cube is $N$ particles of an ideal gas at a temperature $T$. One particle ...
1
vote
1answer
200 views

II law of thermodynamics & polytropic process

The polytropic process is defined as such that $pV^m=A$, where $A$ is a constant. Generally, the change in entropy is $$\Delta S=nR \ln \frac{V}{V_0}+nC_V\ln \frac{T}{T_0}.$$ Using $pV=nRT$ and $pV^m=...
1
vote
0answers
22 views

Is there a word for the availability of a gas, normalized for pressure?

As a bit of background of what I'm getting at, consider that for the purposes of humans breathing and getting oxygen into their blood, 20% oxygen at 1 atm is equivalent to 100% oxygen at .2 atm. ...
1
vote
0answers
48 views

Is it possible to calculate pressure without a barometer?

For an experiment, I need to pump air into a rocket with varying volumes of water, and thus air. However, I want to keep the pressure the same. Given the amount of air a bicycle pump can pump, the ...
1
vote
1answer
651 views

Pressure in a 2D Ideal Gas simulation

I am currently creating a 2D ideal gas simulator whereby the user can determine three of the four variables (P, V, n, T) and the gas would adjust accordingly. I was wondering how I could calculate ...
1
vote
0answers
44 views

How do I calculate the pressure on the walls of my MD simulation?

So I've built a simulation in vpython where I have multiple hard balls that collide with each other and with the walls of the cube I've placed them in. I then replaced the values for their radius and ...
1
vote
0answers
162 views

Entropy density (entropy per particle)

How I can get this definition for an ideal gas: $s=C v \ln (Pρ^{−\gamma})+ \text{constant} $ ? In this answer it is mentioned that there is a connection with the Sackur-Tetrode relation of the ...