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 causes water to be white in a river?

I know it is because of turbulance, causing air to enter the water. But neither air nor water are White, why does the combination of the two make White.
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21 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 ...
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44 views

Can air be considered incompressible as long flow velocities are less than 100 m/s (Ma = 0.3)?

Multiple sources state that steady air flow (in open systems) can be considered incompressible at velocities less than 100 m/s (Ma = 0.3). Example: Deborah A. Kaminski, Michael K. Jensen, ...
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1answer
59 views

Effect of motion of medium on frequency

Will the frequency observed by a stationary observer will remain same if only the medium between the source and observer is moving?(ie. both source and observer are at rest and wind is blowing from ...
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71 views

Amount of Breathable Air in a Depressurized Scuba Tank

The question: How long could a person survive in an airless chamber using only the oxygen released from a 100ft^3 tank containing 32% oxygen? Long version: I'm doing a story on a man who allegedly ...
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10 views

What liquid has the lowest known solubility of O2 at 20°C, 1 atm?

I have recently started a project on hydropneumatic devices, i.e. devices that use hydraulic fluids in conjunction with high pressure gases. In such systems, the most immediate thing you would want ...
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12 views

Excitation of air with the eigen-frequency

I was just wondering (as a layman) what the eigenfrequency of breathable air is? If it exists: what would be the effects of exciting air with its eigenfrequency (w/ regard to humans, matter nearby?)
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2answers
41 views

If an unsealed water bottle has three holes at a different heights, why would the lower hole give out the most water? Is it because of air pressure?

If an unsealed water bottle has three holes at a different heights, why would the lower hole give out the most water? Is it because of air pressure? I am guessing it's because air pressure pushed on ...
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2answers
36 views

Density of air using ideal gas law

I need to find the density of air using (I think) the ideal gas law. I have calculated $V$ of an ideal gas at s.t.p. to be $.0224m^3$. I am asked to find the density of air knowing it's temperature ...
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1answer
25 views

What is the temperature of compress air entering the atmosphere?

Hi to all of you enthusiasts, I have a 1 liter compressed air tank with around 207 bar of air pressure inside. It has been sitting out for a while and I am assuming its temperature has almost reached ...
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1answer
38 views

What amount of force could be created by a person “swimming” in air?

Had a question on a physics test, a person is at rest on a frictionless surface and can not throw anything, can they move? I said yes, by "swimming" against the air and got docked because "it ...
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16 views

power of an engine with wind

I know the power of an engine to overcome air drag is $1/2 c_d ρAv^3$. If the speed of the car $25\ \mathrm{m s}^{-1}$ (relative to the ground) and it travels in opposite direction to a wind at a ...
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29 views

What exactly is Breakdown Voltage of Air?

Most of the online sources say that the breakdown voltage of air is 30kV/cm. I've made a Cockcroft Walton multiplier and I can see the air breaking in between 17-18kV/cm. Only in a discussion at one ...
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3answers
39 views

Wind restistance as function of temperature

Is temperature-dependent wind resistance the reason there's a significant increase in fuel consumption in my Prius car when air temperature drops by 30 degrees K from 300 degrees K? I think I see a ...
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1answer
39 views

Why does the composition of the air does not change with altitude?

Air contains about 78% nitrogen and 21% oxygen independent of altitude (up to 100 km). Why is this? Shouldn't the concentration of nitrogen increase with higher altitudes since nitrogen has a lower ...
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29 views

How can air pollution contribute towards light pollution?

I was just wondering if air pollutants such as soot, could reflect light into the night sky, and thus be a potential source of light pollution. If that's true, can you please suggest any other air ...
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21 views

Calculating optimal heat dissipation/air-flow out-of/into an enclosure - hole size vs number of holes

I am not sure if this is the right place to ask, but I figured it would be a physics question. Essentially I have an enclosure that I will be using to house the components to build a computer. I am ...
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2answers
60 views

Rising glass in xkcd what if

In http://what-if.xkcd.com/6/, Around this time, the glass on the left starts to visibly lift into the air. The air pressure is trying to squeeze the glass and water together. This is the ...
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1answer
69 views

Water vs. Air : Heat Absorption/Capacity

I am not a physicist by any means and not even a current student, but nonetheless I am looking for an answer. Here is what I have gotten so far from university websites and other various resources on ...
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21 views

Affect of temperature and pressure on humidity

If the temperature outside is 0°C and the air is fully saturated, when I heat the air to 21°C without adding any water the relative humidity inside the house would be a very dry 25%. The dewpoint does ...
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1answer
46 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 ...
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1answer
142 views

If my windows are open on a windy day, the curtains sway and the doors slam shut. Why don't I feel this wind?

I am standing indoors, right in front of my open window, as I see my curtains moving back and forth and I can hear my closed doors shaking. I can also hear the wind howling loudly. Why don't I feel ...
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2answers
46 views

Parachute Model

Can you tell me if this model is correct or not? [assuming drag is linearly proportional to the velocity] Considering y-axis vertical and x-axis horizontal,with y positive upwards: 1) ...
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1answer
49 views

Force felt by parachutist when opening the parachute [closed]

When falling down with air resistance, y-axis vertical (positive is up), x-axis is horizontal, we have that: $F_y=-mg-kv=ma_y$, where $k$ is the drag coefficient. Now if the man opens the parachute, ...
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2answers
52 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, ...
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1answer
43 views

Forces in a body falling with air resistance

I would like to know why when a body falls with air resistance, we have that the drag caused by the air is -kv and the acceleration is -mg. What I don't understand is how they both have the same sign ...
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3answers
145 views

Free Fall with Air Resistance

Can somebody help me understanding why when free falling the force on the vertical axis is F= -mg-kv, where k is the constant of air resistance and v the velocity? Suppose the vertical axis is ...
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3answers
71 views

Kitchen physics question I should know.

I don't know anything about physics so this may sound dumb. I punctured a hole on the top of a condensed milk can to drizzle on my snow cone, but when I tried to poor it it barely came out. I randomly ...
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2answers
132 views

If I Blow smoke out my window, will any come inside my room?

My girlfriend and I have got into a lively debate about whether or not my flatmates can smell the smoke I blow out my window. Can you help us? Here is the scenario. The smoker, places himself ...
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2answers
68 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 ...
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1answer
64 views

Is it easier or harder to move moist air with a fan?

From what I understand, the molecular weight of water is lower than the molecular weight of nitrogen and oxygen. So, shouldn't it be easier for a fan to move moist air than dry air of the same ...
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1answer
22 views

Does moving air suck in air from left and right of its path? [closed]

When air is made to move (e.g. by a fan) it has a lower pressure than when it is still. Essentially, this moving air should become a low pressure zone relative to the static air around it and the ...
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1answer
37 views

How do buoyancy control devices (BCD) work?

I get that having more air decreases density and increases buoyancy. However, we can take the diver-BCD-oxygen-tank to be a single system. How can the pumping of air from the tank into a vest around ...
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2answers
120 views

volume of the air bubble in the water

How does the depth affect the volume (the radius) of an air bubble in the water, if the temperature and density of the water are constant. Is there any relation combining this? Can I say that ...
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0answers
36 views

How to restict air flow without reducing pressure

I have a large volume of lightly pressurized air say 10000 cubic feet at 1 psi above atmospheric pressure. I want to move it to another area through a duct which is 20 in by 20 in. Airflow will be ...
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1answer
61 views

Is liquid “air” (nitrogen, oxygen, aragon mixture) flammable?

I was wondering if liquid "air" (nitrogen, oxygen, and argon mixture) was flammable. Imagine you have a container. This container contains liquid air. The air is in liquid form, and is in direct ...
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43 views

Objects and forces: air resistance

A force always works between two objects. When we are talking about air resistance acting on a skydiver for example, would air be considered the second objects besides the skydiver?
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47 views

Can 1km diameter ball of water preserve it's integrity before hitting the ground falling from 10km altitude?

I still argue with my friend over some big ball of water (1km in diameter) that is being instantly created 10km over the surface of the earth in perfect sphere form. I stated, that as it hit the Earth ...
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2answers
60 views

How does the pressure inside car tyre change once the car is lifted/ put back on the ground? [duplicate]

Imagine a car on a jack; how does the pressure change once the car is lifted (all wheels in air - not touching the ground). I'd be interested in knowing whether the pressure will increase or decrease ...
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2answers
241 views

Are raindrops actually “shaped like tears” when they fall?

Raindrops are always pictured like this, people imagine they have this shape when they fall, but is this true? Doesn't this shape create too much drag? What shape do they really have? It would also be ...
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60 views

When does $PV = const$ stop being true?

My problem is the following: a 15-liters cylinder contains air compressed at 370 bar. How many liter will flow out of the cylinder once uncompressed at 1 bar? I thought that I could use $PV = const$ ...
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1answer
51 views

What is the effect of constant wind on a hot air balloon?

If a hot air balloon is being carried by a continuous wind current in a particular direction, in which direction will the flags on its basket wave?
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1answer
51 views

Is single tree shadow locally affecting air temperature?

In other words, is the air temperature under a single tree different from a couple meters away, in a hot day and under the sun? There are several effects potentially interacting: Tree transpiration ...
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26 views

Why does individual N2 molecule rise when heated?

I get that hot air is less dense so it rises due to floatation and all, but what happens to one individual diatomic Nitrogen that it increases it's distance from ground? And why is it that the air is ...
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18 views

Simulating pneumatic tools/devices?

I need to simulate an air compressor/pneumatic system for a train simulator. How do I find the pressure of an air tank after lots of things have used small portions of the compressed air? For ...
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4answers
509 views

Why does moving air have low pressure?

According to Wikipedia lift in an aircraft is due to an area of low pressure formed above the wings of an aircraft due to the fast moving air there. So why exactly is an area of low pressure created ...
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1answer
46 views

Creating airflow in a mini greenhouse [closed]

How do I create the best airflow for a mini victorian style greenhouse, that has a total volume of 80148.75 cm3? I leave the lid on top, which is a triangular prism in structure, open about 2.54 cm. I ...
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2answers
40 views

Atmospheric pressure

What is the significance of atmospheric pressure being referenced as 100 kPa ? Does that really mean 10000 kg/m$^2$ acting upon us ? If we are measuring only collision force on the surface and not ...
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Does forcing air through ever expanding pockets cool it? [closed]

If 30c air is pulled apart then forced back together repeatedly under extraction would this result in a cooling of the air as the energy is lost through a process of constant change?. What kind of ...
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1answer
41 views

can odorous VOCs be removed by an ionizing air purifier? [closed]

I am considering replacing my IQAir HealthPro 250 air purifier by an Electrolux EAP300. According to the marketers, the EAP300 has PlasmaWave(TM) technology that supposedly removes odours from the air ...