Questions tagged [gas]

This tag is for questions relating to "gas", one of the four fundamental states of matter (the others being solid, liquid, and plasma). Gases follow certain laws known as the gas laws. These laws tell us about the behavior of gases i.e., the values and relations of temperature, pressure and volume etc.

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55
votes
3answers
14k views

Why doesn't hydrogen gas exist in Earth's atmosphere?

The root mean square velocity of hydrogen gas at room temperature is: Gas constant: $R=8.31\ \mathrm{J\ K^{-1}\ mol^{-1}}$ Molar mass of hydrogen gas: $M=2.02\times10^{-3}\ \mathrm{kg/mol}$ $$\begin{...
49
votes
6answers
12k views

Why do gases have weight?

I know that a gas is made of atoms or molecules moving freely in space. When these particles hit the walls of where they're kept in they cause something called pressure. But these particles never ...
6
votes
2answers
2k views

Microscopic interpretation of pressure in liquids

Pressure can be explained at microscopic level for a gas with kinetic theory of gases. From that the pressure $p$ is linked to the velocity of molecules (and it is caused by the high amount of ...
13
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4answers
4k views

Why are coke bottles that much fizzier if you shake them?

We've all been there: you drop your bottle of soda at some point and when you try to open it, it bursts into foam. My question is, then: why does shaking a carbonated drink make the dissolved gas ...
60
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18answers
5k views

If liquid and gas are both chaotic states of matter, what's the difference between them on the molecular level?

I'm a laywoman in physics and recently found myself pondering about the matter reflected in the title of this post. To make my question more precise from the mathematical standpoint, let's suppose ...
3
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2answers
486 views

What determines the dominant pressure-flow relationship for a gas across a flow restriction?

If one measures the pressure drop across any gas flow restriction you can generally fit the relationship to $$\Delta P = K_2Q^2+K_1Q$$ where $\Delta P$ is the pressure drop and $Q$ is the volumetric ...
0
votes
1answer
142 views

Compressible gas dynamics in the context of astrophysics

I am looking for a resource that specializes and gives an emphasis on the dynamics of compressible fluids (gas dynamics) preferably in more than one dimensions, but one dimensional is also good, and ...
12
votes
2answers
6k views

How quickly do farts spread?

Basically I started thinking this question in regard to farts. I thought to myself, say Alice and Bob are in a room. If Alice farts, how long would it take for Bob to pick up on the smell? After a bit ...
5
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2answers
4k views

Why do helium balloons rise and fall?

I understand why a regular party balloon filled with helium falls over time due to leakage of the helium. However I've also noticed that recently filled helium balloons put outside rise and fall. At ...
2
votes
2answers
240 views

Why is cold air drier than warm air?

I know this has been asked before but i could not understand the replies. If someone has a simpler answer please do so. My simple Geog lesson just said that warm air molecules are further apart ...
0
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1answer
872 views

Change of temperature of gas in cylinder

Assume we have a cylinder of given volume filled with gas of given temperature and pressure. The cylinder is enclosed from the top by a piston of provided mass. Now, we place a small mass on the ...
1
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2answers
664 views

How fitting is the sound wave (transverse wave) propagation model? (for the layman)

Air is a gas, then how is sound wave propagation possible? I mean, gas particles have a tendency to travel in a straight line, so how does a sound wave occur via compression and rarefaction? Most ...
0
votes
1answer
765 views

What is the speed of air molecule?

Given the minimal temperature measured in the Earth's atmosphere is not $0\space K$, air molecules are moving. I see no reason for air molecule to move all at the same speed. The question is ...
43
votes
1answer
6k views

Why doesn't soda go flat immediately after opening?

So, soda is under pressure and has gas dissolved in it. But, when you open it, the gas is still dissolved in it. But, if we wait a few hours, the gas has escaped into the atmosphere. What factors ...
55
votes
12answers
11k views

Why does hot air rise in a column instead of cold air pressing down?

Ok, this looks like a dumb question or even near trolling, but I really don't understand it. When air is heated over an oven plate, it rises. Obviously, I can check by blowing some smoke in. The ...
6
votes
8answers
3k views

If the probability of a gas molecule to have any velocity is zero then how can the molecule have any velocity at all?

The probability for a gas molecule to have any velocity $v$ is $0$ since there are infinite possibilities for the velocity for the gas molecule to have. If that's so then how come the gas molecule has ...
8
votes
7answers
1k views

What is the counter-force to suction force?

I've been thinking about air pressure and vacuums recently and a (for me at least) interesting question came to mind: If there is an area with lower pressure than the surrounding air, the air ...
7
votes
2answers
342 views

Could the cosmic fluid be better described as a kind of van der Waals gas, or a kind of foam, instead of a dust gas?

In cosmology, it is usually assumed that the cosmological fluid made of galaxies could be described as a gas of "particles" without any pressure (the dust gas), of density $\rho_{\text{matter}} \...
15
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3answers
4k views

What does “rarely” mean in NASA's statement: “technically referred to as an exosphere because it’s so thin, its atoms rarely collide.”?

The following statement is from this article: The behavior of a dense atmosphere is driven by collisions between its atoms and molecules. However, the moon's atmosphere is technically referred to as ...
9
votes
2answers
620 views

How is there still gas in the atmosphere?

The speed of molecules in the atmosphere vary, and can exceed the escape velocity of the earth, $11\:\mathrm{km\:s^{-1}}$ If this happens, and has been happening for millions of years, how hasn't all ...
6
votes
1answer
27k views

Why is the excluded volume 4 times the volume of the gas molecule in van der Waal's Volume Correction Of Ideal Gas Equation? [closed]

Why there is a factor of 4 in van der Waal's Volume Correction?
4
votes
1answer
782 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 ...
12
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1answer
1k views

Why are sound waves longitudinal even though they are mechanical energy?

Waves on a string, ripples on a pond are transverse waves generated by mechanical energy and in the simplest form oscillations. Sound also is a form of energy and basically oscillations. What makes ...
2
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1answer
1k views

Gas permeation through solid metal?

If I make a box from aluminum (0.5 mm thickness) and put air in it (about 2 bar or 3 bar), would the box lose the air over time (10 years period) or not? Assuming the temperature will change ...
2
votes
1answer
272 views

Why doesn't reversible adiabatic expansion generate heat?

In analogy to a compressed gas allowed to reversibly expand and do work, I've been thinking about the behavior of a compressed spring that is very slowly and incrementally relieved of its pressure. ...
5
votes
1answer
627 views

When do ideal gases stop behaving like ideal gases?

Sometimes I don't know which method I should use to calculate the volume of the gas in a system, I'm not sure if I should use the table values for the specific volume, or if I should calculate by ...
2
votes
0answers
117 views

Why In Thermosphere is He and O divided as measured? [closed]

If we look Thermosphere a bit closer. we found out that Helium and Oxygen is divided peculiarily. This picture below shows the Earth looked below the south pole. So the orbiting direction is shown in ...
2
votes
1answer
44 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 ...
1
vote
0answers
219 views

How long does it take for a balloon to deflate?

Since gas flows from an area of high pressure to low pressure, upon opening an aperture on say a balloon one would expect the contents to diffuse out until both the inside and outside reach a pressure ...
1
vote
3answers
3k views

When I open a window to air out the room, how does the smell disperse?

Let's say I'm in a room with some kind of noxious stink, possibly of flatulent nature. The quickest way to right the world that comes to mind is to open a window. When I open a window, how do the ...
1
vote
1answer
567 views

Ventilation shafts in the Great Pyramid [closed]

In the Great Pyramid of Giza, there are four channels, apparently going all the way from inner chambers to the exterior of the pyramid. Archaeologists have speculated that these are ventilation shafts ...
0
votes
1answer
4k views

Outlet temperature of gas through a pipe

I have a pipe, Mica, 2 meters in length. Inner Diameter 8mm, and Outer Diameter 10mm. Thermal conductivity of the pipe is 0.528 $\mathrm{\frac{W}{m^\circ C}}$. I have a gas inlet temperature of 1100°...
0
votes
1answer
87 views

Ideal gas reversible cycle

So I got this cycle on a quiz. As of my understanding, in the transformation 1-2 there is also received heat and given heat ( sorry if that's not the english exprimation, not my first language). Now I ...