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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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
56 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
59 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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0answers
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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0answers
19 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 example,...
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4answers
573 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
47 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
42 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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0answers
10 views

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
46 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 ...
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35 views

how can VOC filters work given that atmosphere has 1800 ppb methane?

I have an IQAir HealthPro 250 air purifier that has a 2.5 kg activated charcoal volatile organic compound (VOC) filter. According to the manufacturer, the replacement interval is from 12 to 24 months. ...
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38 views

Fluid Dynamics - How does air behave out a window?

I often smoke out a window, and I know that if you're driving a car, the passing air will affect the pressure inside and "suck" out the smoke for instance. But what if you're in a window pane? I have ...
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1answer
23 views

How much does humidity affect air expansion in a heated raft tube?

Whitewater rafts that are subject to the sun while off the water, and cold in the water, are subject to significant changes in pressure. In the water this can mean reduced performance due to lower ...
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1answer
28 views

Compute affect of a shower on density altitude

As a pilot I have a basic understanding of density altitude, how temperature affects the effective air pressure: I noticed recently that I have difficulty breathing when I take a shower in Santa ...
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3answers
161 views

Air flow speed and penetration abilities

As I understand, two fans with the same diameter and with the same rotor speed(usually measured in RPM) can have different air pressure(usually measured in mmH2O) and air speed(usually measured in CFM)...
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7answers
2k views

How to keep a helium balloon between 1 to 5 meters above ground? (without it being tied)

I understand that helium balloons rise because their density is less than air, so they can rise up to a point where the air surrounding it has the same weight as the balloon. I was thinking to fill it ...
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0answers
64 views

Bottle cap burst phenomenon [closed]

There is a trick you can do with a simple plastic water bottle: After putting the cap on as tight as you can, you twist the body of the bottle a few times so that it compresses the air in the bottle. ...
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0answers
52 views

Lining up fans in a row

Im new to this website, and not extremely educated in the world of physics. I have a very basic (mostly high school, some college) understanding of physics. That being said, I work for the fire ...
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88 views

Air flow through a tube

During a discussion, a friend explained to me that the volume of air flowing through a tube could be increased up to the point where the air reached supersonic velocity. Presumably the pressure ...
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0answers
23 views

Can I induce draft in my chimney by heating the end of the pipe?

If I were to heat air surrounding the end of chimney cap outside could I create a difference in air pressure such that I could prevent backdraft?
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2answers
150 views

About the real reason why paper doesn't fall in HALF-FILLED inverted cup [duplicate]

I just happen to see a show about air pressure host by Brian Cox. As the link:http://imgur.com/EsRadFi shows, he flipped a half-filled water cup upside down then the paper on cup doesn't drop: It ...
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3answers
89 views

How does inhalation work?

In school, we learn that during inhalation, the diaphragm expands, causing air to get sucked into our lungs. You can feel this suction by putting your hand over your mouth while inhaling. Why is that?...
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1answer
23 views

Air Bearing pressure vs area [closed]

I'm interested in hovering 100 lbs. I'm interested in knowing what pressure of air and what surface area is needed and how they relate to each other.
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0answers
14 views

Generation of negative ions in air [duplicate]

What is the main physical mechanism behind the generation of negative ions in air by a high negative voltage electrode ?
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1answer
327 views

Pressure Calculation - Compressed Air Volume [closed]

I am trying to calculate the change in pressure in a closed pressure vessel that is being compressed. For the sake of simplicity we can consider this to be a syringe with a closed end that is being ...
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2answers
58 views

Why does rolling down opposite windows create a breeze?

If, while driving, I roll down both of the front windows an inch or two, it mainly creates some turbulence around the window. By symmetry we shouldn't really expect anything different. However, if I ...
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2answers
181 views

At what wind speed does wind chill's conductive cooling exactly cancel out the compressive heating of the air?

At relatively slow wind speeds such as 15mph, wind chill drains heat from an object as it flows past, and this conductive cooling effect seems to increase as the wind speed increases. However, at very ...
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1answer
51 views

What laws of physics apply when a flow of air is divided?

The question is rather simple, but I'm not sure if there is a simple answer to it. Let`s say I've got a flow of air (5 bar, 25 l/min) running through a 6mm hose. Then this flow hits a branch dividing ...
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2answers
87 views

Temperature rise in Thermosphere

Generally speaking, temperature decreases as altitude increases from the sea level. But at the ozone layer it increases because ozone absorbs UV radiation. Temperature increases again in Thermosphere. ...
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0answers
51 views

How long does it take for an Oxygen to diffuse around Earth?

We drill into the ground and find a huge pocket of oxygen. How long does it take for that oxygen to diffuse around Earth? I'd like to know for the first oxygen molecule how long it takes to effect the ...
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1answer
122 views

Air friction at supersonic velocities

I know that if an object moves in the air, it can experience two types of drag, laminar and turbulent. For instance, I have a meteor of ideal spherical shape falling from edge of space, say, 100 km up ...
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0answers
116 views

How to calculate maximum wind speed in a funnel (Venturi Effect)?

It must be in an open area, so nothing forces the wind, just himself. Lets assume that the wind is blowing only one direction. I assume that at some point the speed will stop increasing and it will ...
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5answers
4k views

What does air “feel” like to a flying mosquito in terms of viscosity?

If I go for a walk at, say 4 km/hour, unless there is a breeze blowing, I probably won't notice the air around me at all. If I go for a swim though, I will immediately notice the viscosity of the ...
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1answer
104 views

Compressed air cans vs regular compressed air

I have recently learned that when spraying a can of compressed air (the ones you buy in the store) it is very cold and will freeze things especially if you hold it upside down. I know that these air ...
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0answers
29 views

How does air neutralize charged objects? [duplicate]

How exactly does air neutralize charged objects? For example, at what rate does air neutralize a copper sphere of radius R and net charge Q? I assume that the rate may vary depending on the surface ...
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134 views

Using AC with the windows open - will the house cool off quicker?

The other night, a few of my friends and I got into a cool (although some would argue it was heated) argument about the efficiency of cooling a house with air conditioning. I wanted to leave the ...
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0answers
21 views

Temperature and air flow - are they related?

If I open a window, does the air "changes" (e.g. the $O_2$ concentration) in the room more quickly if there was a temperature difference between inside and outside?
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1answer
42 views

Why toilet paper is softer in moist air? [duplicate]

After a hot shower,the air from the bathroom is full of water steam,right? How does the air affect the texture of the toilet paper?I mean,the toilet paper it seems to be softer,but why? Can someone ...
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1answer
233 views

Would opening a car door at high speed change the path of the car? [closed]

If I were to open a standard, four door, four wheel, car on the highway, would the door swing open and possibly tear off? Would the drag that it creates 'reroute' the car (turn it to the direction of ...
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2answers
189 views

What is the air pressure in a bubble of air trapped in an upturned beaker?

If I trap some air in an upturned beaker like this: What will be the air pressure inside the beaker? If I introduce say 10cm3 at atmospheric pressure via a pipe, I guess it will take up a smaller ...
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3answers
2k views

How do suction cups work?

My roommate and I are having trouble agreeing on how suction cups work. Presumably, the ambient air pressure is the only thing which keeps the suction cup attached to the object. When lifting an ...
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1answer
205 views

Air Thermal Conductivity vs Humidity

If air of a certain temperature blows through a car radiator (or a computer case), what effect will air humidity (non-condensing) have on cooling rate?
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1answer
124 views

How relative humidity affects the thawing speed?

I observed that ice cream melts much faster (without much sunlight exposure) when the air is more humid at the same temperature. Eg compare 30C RH 80% vs RH 30% for a typical summer in Hong Kong vs ...
3
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4answers
442 views

Is a turbine the same thing as a motor?

Is a turbine the same thing as a motor? We know that water, wind and nuclear power plants rotate a turbine so is this turbine like a motor? I think we can generate electricity by rotating a motor too. ...
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1answer
107 views

Velocity change of air down a cone?

Does the velocity of fluids(specifically gasses) change when traveling down a cone from the wide opening to the narrow opening? If so, is there an equation used to calculate the acceleration or ...
4
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2answers
558 views

Why does the vortex form in the von Karman Vortex Street?

Why does the vortex form in the von Karman Vortex Street? So far I have this for the reasoning: 'It occurs when a fluid flows around a cylindrical object. The pressure on a fluid particle rises to ...
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0answers
48 views

Visible wavelengths of air fluorescence data - needed for school demo laser telephone design

I'm seeking information about fluorescence in visible wavelengths (390-700nm) of any of the main constituents of air ( $ N_2, O_2, CO_2, H_2O, CO, etc. $) that can be excited with a (hopefully low-...
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0answers
38 views

What is the critical diameter ratio of a cone shaped reducer before air overflows

Let's assume we have a cone shaped cylindrical reducer with $D_1$ inlet and $D_2$ outlet diameter (funnel). Air flows through it with velocity $v_1$ at inlet and $v_2$ at outlet. With the velocity ...
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2answers
173 views

Atmospheric pressure on a flat object

Consider a 10 inch by 10 inch sheet of paper lying flat on the ground. If atmospheric pressure is 15 pounds per square inch (sea level), then there is 1500 pounds of force acting downwards on the ...
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1answer
38 views

If you compress air to a large enough pressure do new molecules form that have a large activation energy?

If you compress air to a large enough pressure do new molecules form that have a large activation energy?