# Tagged Questions

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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### How air humidity affects how much time is needed for heating the air?

In cold weathers it is suggested to put a humidifier since the air gets too dry. I wonder how the humidity affects how much time is needed to get the air at a temperature of 20 Celsius degrees? I mean ...
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### Direction of rotation of a celing fan

From Constellation Energy Quick energy efficiency tip: To stay cool and manage your energy at the same time, use ceiling fans to create a “wind chill” in rooms you are using. The wind chill ...
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### Why do balloons deflate?

Title says it all. Every balloon that I have got, from parties, etc, all slowly deflated for no reason at all. Why is that?
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### A book sits on a table. What is the net force of air pressure?

An elementary problem asks, A book is at rest on a table top. In what direction is the net force of air pressure on the book? Is this a meaningful question, and if so, what's the answer? If ...
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### How can you calculate air resistances at different speeds?

I've read that at 50mph air resistance to an average car is the equivalent of driving through water and at 80mph it's the equivalent of driving through oil. I can't find any references online to ...
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### How to relate speed of sound with relative humidity?

I am exploring the idea of measuring the humidity of a space using sound waves, however I am having trouble finding a mathematical relationship between the speed of sound and the humidity level. ...
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### What is the difference between a puff of air and a sound wave regarding creation and propagation?

While watching a Schlieren video of a hand clapping, I noted a very distinct difference between a sound wave and a puff of air, which were both created by a hand clapping. What is the difference ...
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### wind vs air resistance

I'm wondering which offers more resistance: pulling an object at some speed through air, or holding the object steady against wind at the same speed. I think initially people would think same ...
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### Why don't different air masses mix immediately?

In meteorology, the atmosphere is considered to be divided into air masses, regions of relatively uniform temperature and humidity with fronts on their borders. But why doesn't the air from different ...
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### How would a huge ball of air look in space from outside and from inside?

If you replaced the Earth (except the atmosphere) with air and kept the pressure linear to the center (of the now non-existing Earth) while ignoring the effects this would have on gravity and leaving ...
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### What is the roaring in a roaring fire?

I was just starting a barbecue fire by blowing on the smouldering coals when I realised I had no idea what the sound was actually caused by. I can make the sound by blowing at almost any flame I can ...
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### Physics behind the flow of gas coming out of a balloon

I'm working with stratospheric balloons (latex ones) and I want to put a valve on it so it can float for a longer time. I'm trying to define which valve I should use, which demands I estimate the flow ...
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### Why can I see my breath after I pop my ears?

I have this weird but reproducible thing that I can see my breath for less than a second even in hot/humid weather. The key to do that is to pop my ears - I have to do that often, it's like I'm on a ...
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### atmospheric phenomenon? What causes condensation trails to converge?

This air plane just caught my eye. Two contrails apparently are flowing backward, slightly off-centered and then ultimately converge, giving the overall shape of a very narrow rhomboid parallelogram, ...
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### At what g is terminal velocity not terminal?

How weak would gravity need to be in order for a human to reliably survive the terminal velocity of falling through air? (Context: watching scifi on a space station with a variety of artificial ...
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### Will an air-filled tire normally gravitate toward being nitrogen-filled just by refilling with air?

A big argument by the nitrogen-in-the-tire crowd is that: Nitrogen atoms are bigger and thus less likely to escape the tire, bringing stability to your tire pressure. If Earth's atmosphere is ...
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### What principles does an air glider use?

I just saw this video which was kind of nifty. What principles govern this? Is it simply that 700 lbs of air pressure are exerted from that little 1 HP blower? What would you have to take into ...
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### Can extra-solar gamma rays reach the Earth's surface?

Can gamma rays of high enough energy entering our planet's atmosphere reach the surface (50% probability)? Or, in other words, is there a window for extremely high-energy gamma rays like for the ...
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### Is the wind's force on a stationary object proportional to $v^2$?

I am on a boat docked at Cape Charles, VA, about 30 or 40 miles from the center of Hurricane Irene. This understandably got me thinking about the force of wind on the boat. Since air friction is ...
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### How fast would an object have to move to create a vacuum behind it?

When an object moves, I assume that the air above it, instead of remaining at the same general height, is pulled downward as it is passed in order to fill the low-pressure area behind the object where ...
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### Sum total distance of electrons on a spherical surface

What is the sum total distance between every possible pair of point charges when there are n point charges on a spherical surface? All point charges can only and are located on the infinitesimal ...
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### The visibility of air

For pilots of gliders or sailplanes, the 'thermal' is the most important phenomena of the air. A thermal is classically described as an upward flow of air caused by ground level heating of air that ...
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### What's the name for taking pictures of air flow in a normal room?

There is a way to photograph air in a room. It makes convection, breathing and movement visible. The result looks a bit like a soap bubble. This is some kind of optical effect. No special gases or ...
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### 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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### Make air reflect light

Is there any way in which air can be made to reflect light? By making air denser or by any other way? The task is to project images in air...
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### Can facial surgical mask effectively filter particles of smoke pollution?

Singapore is having an episode of its regular hazy season because of smoke from forest fires. Some people have been using surgical masks like the the one shown at the bottom of this post, presumably ...
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### Dyson Air Blade as a propulsion system?

I've read from many sources that Dyson Air Multipliers are more efficient and quieter than normal fans. Now, with the proof of concept, is it possible to use its principles as a propulsion system for, ...
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### Does a fly get brought up to speed with a bus?

Consider a scenario where a bus is moving at a constant speed and a fly enters through a window,the fly is also flying at a constant speed. Since the bus is not in contact with the fly and neither is ...
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### Why would colder air disperse condensation on a car windshield?

The outside temperature was somewhere between the hot and cold that blows on the inside through the car's vents. I know the condensate is on my side because I can reach forward and write on it with my ...
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### What happens to the air in a water bottle when it falls?

(ignoring the air resistance that causes the bottle to take positions in mid air. Let's say it is dropped in a vacuum with earth's gravity accelerating it downwards) I just cannot catch what happens ...
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### 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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### 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 ...
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### Graph of Electrical Resistivity of Air vs Air Pressure

I've search many place ( Google, forums etc ) but can't seem to find anything that explains the Relationship between: Electrical Resistivity of Air vs Air Pressure Constant Variable: ...
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### Can i use coils with compressed air to make a superconductor?

What im saying is inside pipes i am going to use compressing so that that in the places with low pressure they cool the superconducotor. is this possible? Can i use this concept to make ...
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### Air flow coming out of a fan feels much stronger than air flow coming in. Why? [duplicate]

Possible Duplicate: Why is exhaling more forceful than inhaling? If I put my hand behind my computer's system block, I can feel a very strong flux of air coming out, as it is being pushed ...
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### 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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### 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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### How does a hollow-point bullet move smoothly through the air, presenting a 'cup-shaped' nose instead of an actual sharp-point to the fluid?

Hollow-point rounds move smoothly through the air when presenting a 'hollow cup-shape' instead of a traditional 'sharp point' to the fluid air. Does this mean the air trapped, and at some assumed ...
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### Does measuring the air temperature near a 21 lane asphalt highway impact measurements?

The official temperature in Sydney is measured at the Sydney Observatory. This is located near the city side of the Sydney Harbour Bridge - which is a major highway. My question is Does ...
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### Why the breath sometimes warm and sometimes cold? (2 different explanations!)

If you blow air against your hand with your mouth open, you feel warm breath. If you do with with your lips closed except for a small opening, you feel cold breath. One explanation from here says ...
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### What air pressure is needed on mars, to have fluid water?

The atmospheric pressure on the Martian surface averages 600 pascals (0.087 psi), about 0.6% of Earth's mean sea level pressure. There is a lot of frozen ice on mars, but it can't melt, because of ...
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### Why $e$ in the formula for air density?

I am reading a book that says that the density of air is approximately $D = 1.25 e^{(-0.0001h)}$, where h is the height in meters. Why is Euler's number $e$ used here? Was a differential equation ...
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### What is the difference between air pressure and atmospheric pressure?

I know that air pressure and temperature are inversely proportional. Now I saw in a book that "Atmospheric pressure decreases as we go higher and higher." But at greater heights the temperature ...
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### Are there convective movements similar to those in clouds everywhere in the atmosphere?

I heard there were powerful convective movements in clouds which were responsible for increasing the size of water droplets or ice crystals. My question is: do the same movements appear outside of ...
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### Paradox while Cooling & Heating in Air? [duplicate]

I was thinking about how asteroids get "burned" up in the upper atmosphere as they approach the earth surface due to the atmosphere of earth heating the asteroids immensely as a result of air ...
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### Beryllium Vacuum Sphere Boat/Aircraft

Is it possible to make a solid rigid evacuated "balloon" out of Beryllium or other elements or alloys? The critical buckling pressure at which an evacuated sphere is given as  ...
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### How is a vacuum formed and measured by this pneumatics attachment?

Please excuse me if this question is misplaced and also for my narrow understanding of physics. Firstly, I'm asking simply because the robot I've now been set to work with uses an air pneumatics ...
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### Why would air try to escape from under a pot?

I put a wet Calphalon pot down flat on a wet synthetic countertop. None of the surfaces or liquids was hot. Bubbles started appearing a second or two later from under the rim of the pot in one area. ...