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.
22
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5answers
4k 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 ...
18
votes
4answers
1k views
Why can you “suck in” cooked spaghetti?
We all know that there is no "sucking", only pushing. So how are cooked spaghetti pushed into your mouth? The air pressure applies orthogonal on the spaghetti surface. Where does the component ...
13
votes
4answers
681 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 ...
11
votes
4answers
6k 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 ...
11
votes
2answers
449 views
What is the terminal velocity for a mobile phone
You may have seen the story of the iPhone which was dropped from perhaps 13,500 feet by a skydiver - it survived.
This made me wonder how to work out the terminal velocity for something like that. ...
10
votes
6answers
1k 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 ...
8
votes
5answers
2k views
If I take a bottle of air into space, and open it, where does it go?
It seems to me that space doesn't have any/much air, and if my bottle is full of air, when I open it, where does the air go?
8
votes
2answers
1k 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, ...
7
votes
4answers
516 views
Why does an airplane have more lift near the ground?
I've noticed that an airplane appears to have more lift when it's almost touching the ground then it has 100 feet or more in the air. What causes this to occur?
6
votes
5answers
2k views
Does it take significantly more fuel to fly a heavier airplane?
I was reading in the papers how some-airline-or-the-other increased their prices for extra luggage, citing increased fuel costs.
Now I'm a bit skeptical. Using the (wrong) Bernoulli-effect ...
5
votes
3answers
258 views
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 ...
5
votes
3answers
906 views
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 ...
5
votes
1answer
434 views
Paper plane between two fans - is this possible?
The setup: two fans facing each other, distance around 1m. Both are turned on. In between them, place a simple paper plane and according to this video, it will fly.
...
5
votes
1answer
184 views
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 ...
5
votes
1answer
466 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 ...
5
votes
3answers
834 views
Including air resistance, what is the escape velocity from Earth?
Including air resistance, what is the escape velocity from the surface of the earth for a free-flying trajectile?
4
votes
3answers
225 views
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, ...
4
votes
5answers
743 views
Is it possible for wind to break the sound barrier?
I understand that in nature wind would never get high enough, but I am just curious as to whether physics would allow this to occur or not.
4
votes
5answers
635 views
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 ...
4
votes
2answers
116 views
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 ...
4
votes
1answer
112 views
Why do wind power plants have just 3 blades? [duplicate]
Why do wind power plants have just 3 blades? It seems that adding more blades would increase the area that interacts with the wind and gather more energy.
(Image from Wikipedia.)
4
votes
1answer
132 views
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 ...
4
votes
2answers
244 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 ...
4
votes
1answer
267 views
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 ...
4
votes
2answers
2k views
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 ...
4
votes
2answers
124 views
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 ...
4
votes
1answer
173 views
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 ...
4
votes
0answers
147 views
Why is it hard to breathe when cycling against the wind?
Sometimes when I bicycle against hard wind, I find it difficult to breathe. Others I have discussed it with have also noticed this effect.
A possible related phenomenon that I heard from an ...
3
votes
2answers
3k 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 ...
3
votes
3answers
122 views
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 ...
3
votes
2answers
564 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 ...
3
votes
2answers
217 views
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 ...
3
votes
2answers
530 views
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 ...
3
votes
2answers
118 views
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.
...
3
votes
2answers
645 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 ...
3
votes
1answer
105 views
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 ...
3
votes
1answer
1k views
What does the wind speed have to be to blow away a person?
With the approaching hurricane, I am curious about what would happen if I go outside, in particular whether the wind gusts might be fast enough to blow me away. How fast would the wind have to be to ...
3
votes
3answers
271 views
Does launching a rocket in lower density air require more or less fuel?
Given two environments that are identical, except for air density (e.g. Cape Canaveral, but at Mount Everest's height), would launching a rocket require more or less fuel at the lower air density?
3
votes
1answer
79 views
Influence of air resistance in space
Consider the following situation:
You are locked inside a cylindric container allowing you to move around freely without being in contact with any of the items or surfaces aboard. The container is ...
3
votes
3answers
368 views
How would you move without gravity?
I'm wondering how would you move without gravity? You would still have air pressure at 1Atm.
Would you "swim" in the air or would you have do something else?
3
votes
1answer
244 views
What kind of curve would describe the rate of air coming out of a balloon?
If one graphed the volume per time of air being expelled from a common elastic balloon out of a hole of constant size relative to the balloon's surface area, would the curve of the graph be ...
3
votes
1answer
202 views
Local Mach number for an airfoil
I would like to know how to calculate the local Mach number on the upper surface of an airfoil given the ambient temperature, the local velocity on the airfoil surface, the freestream velocity, and ...
3
votes
1answer
175 views
Fluid Dynamics: Bernoulli Air Tunnel
I have the following question as part of a lab intro to explain the more complicated stuff I'l actually have to submit in the lab. I put all the questions here just to show my thought pattern/what ...
3
votes
2answers
283 views
Alcohol inside a container
Let's imagine a plastic container completely closed. We put alcohol inside it filling it at half. Now we make a hole to introduce 2 little Conductor one near the other so that they don't let the air ...
3
votes
0answers
35 views
How long would it take for a container in vacuum to leak half of its air?
Let's say I know the size of the container, size of the hole the air leaks through, pressure the air is under and temperature of the air if that helps anything. Is it possible to calculate this only ...
3
votes
3answers
260 views
Ozone Hole in the South Pole
Perhaps this should be a chemistry question, but it seems to have physics attributes. There's a perennial ozone "hole" around the south pole created by destruction from Cl based chemicals like CFCs. ...
2
votes
2answers
148 views
Why is a hole in a ball?
I wanted to know why there is a hole in the ball (basketball, volleyball, handball) to fill the ball with air. Why can't the ball come with filled in air and fully sealed so that there is no loss of ...
2
votes
3answers
260 views
Why does air remain a mixture?
As we all know, air consists of many gases including oxygen and carbon dioxyde. I found that Carbon dioxyde is heavier then O2. Does the volume difference neglect the mass difference? Is it same for ...
2
votes
1answer
2k views
Sound - what happens with the particles when a wave passes
I'm having some problems in understanding the principles of sound propagation. The wave propagates though air (for example) exerts compression, which is followed by rarefaction. I think I got than ...
2
votes
2answers
503 views
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 ...
