# 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
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 ...
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 ...
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 ...
481 views

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 ...
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 ...
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-...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
833 views

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. ...
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 ...
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 ...
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 ...