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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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11
votes
1answer
1k views

A flying fly inside a sealed box on a scale

suppose there is a scale able to measure weight with an uncertainty of $10^{-9}kg$ . On the scale, an airtight plastic chamber is placed. Initially, a fly of mass $10^{-5}kg$ is sitting at the bottom ...
100
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12answers
23k views

Why is filling a balloon from your mouth much harder initially?

Why is it that when you first fill up a balloon, it's hard to get air through, but after inflating it a bit, it becomes much easier to further inflate the balloon?
32
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4answers
106k views

Why does the air we blow/exhale out from our mouths change from hot to cold depending on the size of the opening we make with our mouth?

Why does the air we blow/exhale out from our mouths change from hot to cold depending on the size of the opening we make with our mouth? It's not just a subtle difference, but significant in my ...
53
votes
6answers
101k views

Why is jumping into water from high altitude fatal?

If I jump from an airplane straight positioned upright into the ocean, why is it the same as jumping straight on the ground? Water is a liquid as opposed to the ground, so I would expect that by ...
27
votes
4answers
35k views

Why is the pressure inside a soap bubble higher than outside?

Apparently, the air inside a soap bubble is under higher pressure than the surrounding air. This is for instance apparent in the sound bubbles make when they burst. Why is the pressure inside the ...
37
votes
5answers
26k views

Why do heavier objects fall faster in air?

We all know that in an idealised world all objects accelerate at the same rate when dropped regardless of their mass. We also know that in reality (or more accurately, in air) a lead feather falls ...
18
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7answers
6k views

Why is air invisible?

I think that something is invisible if it's isolated particles are smaller than the wavelength of visible light. Is this correct? Why is air invisible? What about other gases and fumes which are ...
36
votes
4answers
134k views

On a hot day, when it's cooler outside than in; is it better to put a fan in an open window pointing inwards or outwards?

If it's really hot inside, but cooler outside; what is the best way to place a single fan to try and cool a room down? I always assumed it would be better pointing inwards (and this thread suggests ...
18
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6answers
674 views

Reason for strange “canyons” of dust on the cooling platform

I took apart my cooling platform Something like this : And I found something like this inside : I wonder why around the hollows are the "canyon like" structures. PS: I also drop this platform on ...
23
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5answers
59k views

How does the Eco-Cooler air conditioner really work?

This article describes a device for developing countries which apparently cools the air by 5 °C without electricity. According to its YouTube video, it works by lowering the pressure to drag in the ...
3
votes
2answers
36k views

Calculate flow rate of air through a pressurized hole

I was wondering about this: If there is a pressurized container, like a tank of compressed air at some pressure that is greater than the ambient air pressure, and this tank of air has a hole in it, ...
2
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3answers
17k 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 ...
7
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2answers
2k views

Beryllium Vacuum Sphere Boat/Aircraft [closed]

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 $$ P_1=\frac{2E\cdot\...
41
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10answers
25k views

Why can't we see gases?

I am not sure what causes gas molecules to be invisible.This question may look silly but I really want to know the story behind it.
43
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6answers
6k views

How much air needs to be displaced to generate an audible sound?

I'm reading a book where in one scene a wizard/alchemist teleports a scroll after reading. He folded the parchment carefully and muttered a single cantrip. The note vanished with a small plop of ...
25
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4answers
33k views

If air cannot conduct electricity, how can lightning happen?

If air cannot conduct electricity, how can lightning happen?
22
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2answers
3k views

Why does blowing on a candle put it out but sucking doesn't?

Alternatively, why does the force created by blowing out air feel so much stronger than the force created by sucking in air? Ok, so forget the human factor involved in blowing out candles. Consider a ...
11
votes
2answers
3k views

Inflating a balloon (expansion resistance)

I am doing a quick calculation on how to calculate the pressure needed to inflate a perfectly spherical balloon to a certain volume, however I have difficulties with the fact that the balloon (rubber) ...
9
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2answers
5k views

How did Enrico Fermi calculate the classical Fermi Problem?

From Wikipedia: Fermi was known for his ability to make good approximate calculations with little or no actual data, hence the name. One example is his estimate of the strength of the atomic bomb ...
22
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2answers
19k views

Is there an upper frequency limit to ultrasound?

Wikipedia has this diagram of the acoustic frequency spectrum: Is there an upper limit to the frequencies you can transmit through the air? Are they absorbed more and more at higher frequencies, ...
53
votes
3answers
20k views

Will helium in the tires of a bike make it lighter?

I know that helium balloons float because it is less dense than air. I'm not expecting my bike to float, although that would be pretty cool. I just wanna know if replacing normal air with helium in ...
30
votes
3answers
22k views

If aerographite is lighter than air, why doesn't it float?

Air is 6 times denser than aerographite but looking at pictures or videos presenting the material, I see it resting on tables rather than raising to the ceiling. Also, since the material is made of ...
7
votes
3answers
53k views

Can pockets of air exist underwater?

If yes, why don't they fill up with water, and can you breathe the air there? Like, it's not exactly atmosphere there, but an underwater cave with higher ceiling. P.S. Possible that it has a ...
4
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2answers
832 views

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 ...
17
votes
4answers
2k views

Why is exhaling more forceful than inhaling?

By blowing at pencil, a piece of paper, or another object up to fifty centimeters away, I can cause it to move away from me significantly. But I can't move an object toward myself by inhaling sharply ...
6
votes
1answer
2k views

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: Temperature ...
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3answers
3k views

Why does air remain a mixture?

As we all know, air consists of many gases including oxygen and carbon dioxide. I found that carbon dioxide is heavier than O2. Does the volume difference neglect the mass difference? Is it same for ...
4
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8answers
8k views

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 "...
3
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4answers
1k views

Would we be able to hear the sun if space were full of air?

I was wondering if the sun could be audible from earth in an air-filled space scenario. We can ignore all the other disastrous consequences! Thanks!
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2answers
2k views

Fan Speed Formula

Is there any formula for computing fan speed by using air mass,air flux, air density or specific heat? I have computed air mass and air flux, and found the values for air density and specific heat, ...
3
votes
2answers
1k 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 ...
2
votes
1answer
2k 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 ...
2
votes
3answers
8k views

How can sound waves propagate through air?

We know that the sound waves propagate through air, and it can't travel through vacuum. so the thing that help it doing that is the air's molecules pressure. So my question how can that happens? I can'...
2
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3answers
1k 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 ...
1
vote
1answer
1k views

/HVAC/ Air speed and influence on human body

I was wondering about three things: Wind chill effect. Human body perceives surrounding temperature as colder, with increasing air flow: (Image on wikipedia) This is understandable, as thermal ...
1
vote
2answers
549 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
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2answers
797 views

Weighing a flying bird [duplicate]

Let thing of a bird standing still in a box on top of a weighing machine that shows a mass $m_0$. Now, imagine that the bird is flying, still in the same box and the same weighing machine shows a mass ...
-2
votes
4answers
13k views

If hydrogen and helium are lighter than air, why won't liquid hydrogen and liquid helium defy gravity?

Title says it all. If hydrogen and helium are lighter than air, why won't liquid hydrogen and liquid helium defy gravity?
75
votes
1answer
25k views

Why do chimneys have these spiral “wings”?

While walking around I noticed something very peculiar. Many chimneys had spiral "wings", while others didn't. I came up with two possibilities: The wind circles around the chimney upwards which ...
31
votes
5answers
4k views

Why don't things get destroyed by gas molecules flying around?

Gas molecules go at an insane velocity, and though they are miniscule, yet there is a LOT of them. Of course, because of all these molecules hurtling around, there is air pressure; yet if you envision ...
23
votes
6answers
38k views

Why does my door shut faster when the window is open?

I've noticed that if I shut my door when the window is open in a room, the door will tend to shut faster. If I shut the door when the window is closed with a normal force it will not fully close as if ...
34
votes
7answers
8k views

Is it possible to “cook” pasta at room temperature with low enough pressure?

It is known fact, that boiling point of water decreases by decreasing of pressure. So there is a pressure at which water boils at room temperature. Would it be possible to cook e.g. pasta at room ...
30
votes
6answers
30k views

Why does a tire need to be filled with air?

The Mini 4WD's tires aren't full of air, and it can run. Also, the tank doesn't have tires with air. So, the question is: why do real cars on the road need to be filled with air? What is the idea ...
21
votes
4answers
5k views

Why do bubbles make a sound?

I have an understanding of how bubbles work. They encapsulate air (or other fluids) in a membrane caused by surface tension. When they pop, there is often a sound. Sound is a type of energy, kinetic ...
14
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2answers
11k views

When blowing air through a tube, why does it act differently if I press the tube against my mouth, or hold it an inch away?

So I have a tube of wrapping paper. It's at least a couple of feet long and maybe two inches wide. If I press one end of the tube firmly against my mouth and blow, I barely feel warm air come out ...
11
votes
3answers
14k views

Is it possible to make laser beams visible midair without smoke?

My question is: Is it possible to make laser beams viable midair without smoke? I thought it would be a great idea to have a (second) smartphone or pc screen without having a solid screen. The reason ...
1
vote
2answers
44k views

Why do particles in high pressure air always flow to lower pressure?

The title really says it all: Why is this case? A "Feynman type" answer would be really appreciated as I'm more of a layman that a physicist.
9
votes
3answers
33k views

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 ...
8
votes
1answer
51k views

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?
6
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3answers
3k views

The physics behind Balloons lifting objects?

Apologies for the super basic question, but we all have to start somewhere right? Can somebody please explain exactly how you would calculate the number of helium balloons it would take to lift an ...