Questions tagged [air]

Earth's atmosphere is a layer of gases that surround it, permitting life and protecting life by absorbing ultraviolet solar radiation, warming the surface by retaining the heat and mitigating the temperature difference between day and night.

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What makes air exist as a physical yet almost homogeneous mixture with no difference in concentration across regions?

You would think air being a physical mixture there would be changes in N2:O2 molar ratio across regions. But we all breathe more or less same composition of air, right? How come?
daraj's user avatar
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2 answers
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When the air can be regard as incompressible and how to get this conclusion?

The air density changes negligibly when the air velocity $<0.3$ Sound velocity, so in this case it can be regarded as incompressible, How to get to this conclusion?
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What kind of vacuum would you achieve if you used a compressor in reverse rated at 8 $\rm bar$? (centrifugal, piston or axial if it matters) [closed]

If you used for example a centrifugal compressor that compresses air from an intake of 1bar to 8bar in reverse, what would be the vacuum achieved in mbars? Can a compressor even work with an ...
Andi Iacob's user avatar
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How do I extrapolate a value of oxygen particles per million from vacuum pressure Pa/torr

If I have a box of 40 $\text{cm}^3$, with ambient pressure and oxygen, how could I extrapolate and bring down the oxygen level to say 500 ppm from an equation such as $1.33 \times 10^{-4}$ Pa ($1 \...
Andi Iacob's user avatar
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1 answer
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Within close proximity, how much does the atmosphere influence light and thus what we see?

Not sure if this is the best place to ask. Apologies if not. (Assume this is under generally average conditions) Say you have an object that is 1 metre in front of you. When you see that object, how ...
ACrypticFish's user avatar
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The suction and thrust of an aircraft engine

Does only the air sucked in (not the air that is ejected at the back of the engine) by an airliner engine (turbofan engine) causes a thrust forward or in other words pull the engine forward? and why ? ...
Sebastyen Laroche's user avatar
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1 answer
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Is atmospheric pressure on an object in vertical plane equal to that of horizontal plane? [duplicate]

Suppose there is a cubic object placed at a surface level. Will the atmospheric pressure exerted on the upper surface of it be equal to that of the pressure exerted on its sides? As far as I know ...
MSKB's user avatar
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Filling the empty bottle with hot air

If I were to fill the empty empty bottle with hot air, how can it be done? If I leave the bottle out in the sunny weather, will the bottle fill with hot air? When I am filling the empty bottle with ...
Kıvanç Cantimur's user avatar
2 votes
3 answers
771 views

What makes longitudinal waves work?

I am quite confused by what makes a wavefront that is part of the compression (line A) turn back towards the rarefaction area. Lets say that the sound is propagating left to right in the image: What ...
Dimitri's user avatar
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Does it follow that hot air is always replaced by cold air? [closed]

A cylinder contains a powder made up two substances - spherical grains of metal and spherical grains of plastic. In between the grains are voids, so that the cylinder is made up of 75% powder grains ...
EddieP's user avatar
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Can you make $\rm H_2O$ out of the air with tools anyone has? [closed]

I was just wondering if you could make $\rm H_2O$ out of the air with tools that everyone has?
Jayden Rochford's user avatar
16 votes
4 answers
8k views

Why do raindrops look like sticks?

I always thought that raindrops look like this emoji 💧. But today, I shot it in slow-mo (see on YouTube), and they look more like sticks. Was it some light effect of my camera, or do they really look ...
Ilya Gazman's user avatar
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UV-absorption capability of air

I am looking for an absorption chart for UV light with a wavelength of around 250 nm in air (ambient, no specific preparation). How much of a beam of this light would be absorbed per meter of path ...
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2 answers
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If you decreased the mass of a planet, but kept the mass of the atmosphere the same, would the air density decrease?

So, I know that atmospheric pressure is a result of both the atmospheric mass and the force of gravity acting on it. If you were to decrease a planet's gravity, but keep the atmospheric mass the same, ...
Elhammo's user avatar
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Snorkeling vs diving with a breathing cylinder

If diving with 5m snorkeling pipe our lungs would collapse due to 0.5 atm difference, right? If diving with a cylinder that has air with atmospheric pressure (the pressure our lungs can use), we can ...
Lukasz Skowron's user avatar
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1 answer
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Is it possible make a train moving with less atmospheric friction if a pressurized air shield is applied at its frontal part?

Like the magnetic field blocks radiation particles approaching Earth could a pressurized air pipe at the frontal part of a train block atmosphere that constantly slows down that train? The pipe should ...
jbradvi9's user avatar
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Dust Estimation technique

I'm comparing different coating agents for ammonium sulfate fertilizer granules, coating agent is an additive to limit the dust emission, so I have a new coating agent that is lower cost and more ...
R4Mii's user avatar
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114 votes
4 answers
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Why do clouds have well-defined boundaries?

Why do cumulus clouds have well defined boundaries? In other words, what are the physical mechanisms that hold a cloud together, as an entity separate from other clouds, that prevent it from spreading,...
Roger V.'s user avatar
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Equation for Velocity of air and Pressure difference

Whenever there is a pressure difference, air will flow from the high pressure (area/point) to low pressure (area/point). I am looking for the equation that relates the velocity of air to the pressure ...
Alex's user avatar
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2 votes
3 answers
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Could a glass cup containing a vacuum rise into the air?

https://what-if.xkcd.com/6/ has been mentioned here before, but I'm questioning whether or not the glass cup with the bottom half as a vacuum would rise at all. To start with, a vacuum exerts no force....
Rob Watts's user avatar
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Optimisation of pop pop boat?

This beautiful video of Steve Mould explains the working of a pop pop boat using a glass boat. Now he explains that the pop pop boat doesn't move because of ejecting water in one direction like a ...
Srinivas N Rao's user avatar
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How, if, does the inside air of a football influence it's motion?

And before me lies a football. Say it's filled with pressurized air. If I kick it, how will the inside air be influenced? Will the kick induce soundwaves? Can the ball give a sound? Will it influence ...
MatterGauge's user avatar
1 vote
0 answers
24 views

Why doesn't an air valve move automatically when placed on a zero friction surface?

Air pressure is actually a force experienced by the surface of the container when air molecules hit it in high speeds. An air valve opens and allows air to move in one direction and blocks the the ...
Srinivas N Rao's user avatar
1 vote
1 answer
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How to harvest water passivley?

I have been reading recently about methods to collect moisture from the air passively and turn it into water. However, is there any attempt currently for small-scale water harvesting? Methods I have ...
Anwer Ak's user avatar
1 vote
1 answer
89 views

What is the theoretical range of temperature the air must be in order to reflect/refract light (for a volumetric display)?

Well, the only question I found in this website about volumetric displays on air was this one, but it specifically suggests making air denser in order to make it work, but my question is specifically ...
Fulano's user avatar
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0 answers
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Why does Hoberman sphere open when thrown up? [closed]

Please try and explain this to a dummy :) I haven’t had any university level physics education, at least yet. I was messing around with a mega sphere (Hoberman sphere toy) at a family dinner when I ...
Silber's user avatar
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1 vote
1 answer
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Equilibrium of air volume in and out of an inflated bag

I want to use a small squirrel cage fan to blow air into (and inflate) a closed bag. The bag will also have a number of small holes in it to release air at various points across the bag. But, I want ...
ellipsed's user avatar
2 votes
1 answer
163 views

How to Model the Forces within Inflatable Tube Man

I have a CPP setup for a cloth simulation. Currently it takes in forces for wind simulation and gravity and these forces act on individual "point masses". I'm trying to figure out how to ...
Melanie's user avatar
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1 answer
173 views

Hole in Bernoulli's theorem when trying to blow ball into bottle

According to Bernoulli's theorem while blowing a paper ball inside the bottle (as shown in this short video), the speed of the air at the mouth of bottle is higher and hence creates low pressure ...
Dhanesh Khurana's user avatar
1 vote
1 answer
54 views

How does air cool as it nears the poles?

I understand air is heated by the equator causing it to rise towards the poles. But why does air cool and sink after nearing the poles. Shouldn't the air still possess heat, after being heated by the ...
Howard Stark's user avatar
1 vote
1 answer
123 views

Warm air syphon to cool down greenhouse

I'm thinking about a very energy efficient way of controlling temperature inside a greenhouse when it's too hot. The goal is to use the syphon effect in order to draw hot air from the top of the ...
enapupe's user avatar
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0 votes
1 answer
48 views

How does (air) pressure balance under constraints?

I'm playing around with building a very basic simulation of (air) pressure in a grid environment. The idea is that I have this 2d (or 3d) grid of cells. Each cell has a certain atmosphere. Between the ...
kwiesmueller's user avatar
2 votes
1 answer
260 views

Do forests create wind?

Forests evapotranspire more water vapor into air than surrounding areas, have more clouds, and are usually cooler (because of evaporative cooling). How does this affect the air pressure of forests? ...
mudpuppy's user avatar
3 votes
2 answers
2k views

Why doesn't pressure affect the speed of sound in air? [duplicate]

I keep getting the answer "because density increases when pressure increases" but that doesn't really make sense to me since in denser materials - like water - sound travels faster. And if ...
Schrodinger's user avatar
0 votes
1 answer
41 views

How come air masses displace air when it moves rather than mixing with it? [duplicate]

It seems if you had one mass or air moving towards another air mass, that the molecules within that first air mass would be able to penetrate into the second air mass because the distance between air ...
mudpuppy's user avatar
0 votes
1 answer
189 views

Can Stoke's Law of Viscous Force be applied to freely faaling body?

As air is a viscous fluid can we apply Stokes Law to freely falling bodies. By doing this we can see that the velocity of a freely falling body doesn't increase with time but it stops increasing after ...
Satya Raj Shivareddypeta's user avatar
0 votes
2 answers
115 views

Why not a heat pump with only the outdoor air?

I was wondering why we can not use only the outside air for a heat pump? Taking the outside air, pass it through a compressor to increase pressure and temperature. Then the hot air flow heats the area,...
Jejouze's user avatar
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0 answers
33 views

Bird drink feeder -- How to make water come out automatically and stop coming out from a bottle? [duplicate]

I am watching a video about a DIY bird water feeder. https://www.youtube.com/watch?v=q6EitavSRNg In the video, three holes were punched from the plastic bottle in a triangular pattern, and then the ...
GreenPenguin's user avatar
4 votes
1 answer
202 views

Why is ozone $\rm O_3$ in the Earth's upper atmosphere?

If you look at the density table, you will see that ozone has the highest density among other gases, so why is it in the upper layer of the atmosphere, in the picture I schematically drew how the ...
Fakt309's user avatar
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0 votes
1 answer
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Room ventilation during summer

I can never get this right =) I have a main living room with air con running in summer. But CO2 levels build up. Now its evening and I want to vent the room but without the room getting too hot again (...
Sergey Fox's user avatar
1 vote
0 answers
137 views

Can you remove air bubbles from oil by heating it just like you do with water? Does oil even have dissolved air?

I have a flat bottle filled half with water and top half with oil. It has a impeller connected with motor which slowly swirls oil and water to create beautiful lava lamp like effect. However after ...
Aamer Jalal's user avatar
0 votes
2 answers
55 views

Thermal power station powered by temperature difference between high and low altitude air

Would it be feasible to build a system where warm air from sea level is pumped to the top of a mountain to power a thermal power station? With a lapse rate of ~ 1°C / 100 m there should be plenty of ...
adius's user avatar
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0 answers
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Equation to find the velocity of gas

Air travels from a hot place to a cold place. Is there an equation that shows the relation between velocity of gas (specifically air) and difference of temperature between two points?
Alex's user avatar
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1 vote
3 answers
6k views

Does indoor odor smell travel up or down?

Does odor smell, let's say it's from caulk off-gasing, travel upward or downward in the air? Are all odor smell lighter than air?
user1187968's user avatar
1 vote
2 answers
110 views

Would lotion pumps work in a vacuum?

I'm just trying to understand how a lotion pump works. I watched this video and it's explained that it's due to the difference in air pressure. https://www.youtube.com/watch?v=EJVL5zXIPLA&...
Mac_79's user avatar
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1 vote
0 answers
20 views

Ventilation - Push system into Pull system, what can happen [closed]

this is my first question so please go easy on me. I have a system where it pulls air out of a sealed box at ~500l/min (this sealed box has a requested pressure of 10Pa, in case it is relevant). The ...
Rick's user avatar
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3 votes
2 answers
261 views

At what speed would a wind affect a bullet? [closed]

Firing a gun loaded with the fastest bullet (.220 Swift 1,422m/s or any bullet that is super fast and excellent aero dynamics) in a close range (2cm) from the tip of an air blower. What would be the ...
Hither Joe's user avatar
20 votes
4 answers
9k views

Does the amount of oxygen in air, actually get lower as you go to higher altitudes?

I have heard that there is less oxygen as you go higher (that's what my teacher told me). A reason that supports that is, as you go to higher altitudes, it becomes more and more difficult to breathe. ...
Ishaan Manish's user avatar
16 votes
3 answers
2k views

How does a virus fall down in static air?

If we drop a virus from a height, in static air, will it fall to the ground like a lead ball, a balloon, or like a virus? How will it fall to the bottom? Like a Brownian particle? It will not float ...
MatterGauge's user avatar
2 votes
2 answers
76 views

Could super-heated gas allow for Dirigibles/Zeppelins/Balloons to go higher than 60 km of altitude?

Well, I don't know much about physics in general, so I hope I don't make too many misconceptions. So, from what I could read in this Wikipedia article, the balloon named "BU60-1" achieved ...
Fulano's user avatar
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