# 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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### Does pressure decrease on the skin of an object at extreme speeds?

A few things before I start: Air molecules move at a set speed given the temperature is the same. Pressure is how much force these molecules exert on a surface. Here is a sketch I drew (excuse the ...
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### Why don't liquid aerosols rapidly vanish by evaporation?

Liquid aerosols are known to be relatively stable. However, given their immense surface area and tiny volume, we would expect them to rapidly vanish by evaporation. Why are liquid aerosols ...
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### Pressure of column of air and pressure of cinder block - what makes the pressure to apply from below in the former and not in the latter? [duplicate]

Pressure is force per unit of area. I understand that the pressure at the ground is the force the column of air (above a surface of one square meter) exerts on that surface of one square meter. To be ...
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### Will the pressure on the high-pressure side of a moving object in air be mirrored by an equal but opposite pressure on the low-pressure side?

Say you have an atmosphere of room temperature, sea level, 0% humidity air. Then, imagine you have a steel cube moving through the air with one of the six faces directly into the wind. If it’s moving ...
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### Does air filling a vacuum produce a force?

Imagine you have a vacuum chamber set at a complete vacuum, and there is a valve to let air in. If you open this valve, the air molecules will start moving into this empty area, eventually filling it. ...
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1 vote
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### Brilliant's question on air pressure

I have always thought that as temperature increases the pressure does as well in an ideal gas, of course I know the air in the atmosphere isn't exactly an ideal gas but I would've thought that the ...
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### What is the pitch or air flow constant of a whistle?

I am making a whistle capable of making any sound and/or frequency based on a specific air flow, but despite my personal goal, What is the pitch or air flow constant of a whistle? I mean to express, ...
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### Best direction of air flow in peltier based air dehumidifier?

I'm currently designing a peltier element based air dehumidifier and need to decide which direction of air flow trough the device makes more sense. The possibilities are either directing the intake ...
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### Why don't disturbances/wind move at the speed of sound in air?

Why don't sound waves move at the same speed as air that has a pressure differential? Imagine you have a box that is filled with air. One half high pressure air, the other half low pressure. They are ...
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### Calculate number of air particles going through a hole in high vacuum at molecular flow

I have a vacuum chamber, connected to a vacuum pump with a pipe of diameter 50mm and need to create a high (0.0001mBar) vacuum. I need to calculate the total suction time, and since I was not in the ...
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### Is air resistance truly linear in surface area?

Air resistance is generally said to be linear in the surface area of the moving object. Out of pure curiosity, I am wondering to what degree this is an approximation, i.e., when this assumption begins ...
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### If air was the same density as water, but still a gas, could you swim in it?

I'm not talking about normal physics here, as it would be extremely hard to get such a situation to arise, this is more a hypothetical question. If air was the same density as water, while still ...
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### Variation of fan air temperature with angle

On a very hot summer's day, I was on my porch using an electric fan and I noticed that the air it blew had different temperatures. As you move away from the center and towards the outer border, I ...
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### Does compressing air increase the average speed of the air molecules?

If you have a cubic foot of air and compress it, will the speed of the molecules stay the same or increase? I know that the air will heat up the surrounding objects because the molecules are in a more ...
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### What would happen if a human completely disappeared?

How strong effect would roughly human sized and shaped vacuum spontaneously appearing at sea level have? This event is completely fictional. This is related to: What would happen if a piece of matter, ...
1 vote
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### Hot dust contribution to whirlwinds forming

My father observed an event with a whirlwind and had an aha moment on its forming. What he saw was a weak wind blowing over a sun heated patch of dust, and when the dust rose up, all of suddenly a ...
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### How does energy become sound?

From my understanding energy and matter are interchangeable ($E=mc^2$). Also, motion requires energy, but energy does not require motion. Now, for my question, as an example, I will use the chain of ...
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### Balloon volume as it rises in constant atmospheric density

I've been considering an hypotetical situation and it's making me a bit confused. If anyone could give me any insight, I would really appreciate it! It is as follows: Let's pretend atmospheric ...
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### How does the rate at which we enter air at lower pressure affect whether air bubbles will get stuck in our blood?

When we, for example, scuba dive, we will breathe air at higher pressure, hence the amount of dissolved gas in our blood will be higher (Henry's law) (right?). Now when we come back to normal pressure,...
1 vote
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### Is it possible to calculate weight with air pressure?

i was wondering if it was possible to calculate a mass of object on top a bag filled in with air as compared to a bag of air filled up with nothing on top of it assuming the air pressure going into ...
1 vote
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### For hot air at 150 °C have a density of 0.61 kg / m³, how to calculate the density for 160 °C? [closed]

I am working on a project draft and in an existing device, hot air up to 160 °C is generated for drying processes. I have found old documents where densities of air are reported at three different ...
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### Can I get burned with warm air?

If temperature is the "average" result of measuring a mix of hot and cold air particles, then I can be in a room of some warm temperature but being hit with both extremely hot particles and ...
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### Formula for air density given temperature, pressure, humidity

What is a good formula for air density (kg/m^3) given temperature (°C), pressure (hPa), and relative humidity? I tried implementing the formulas from here as follows: ...
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### How to determine air flow required? [closed]

I am making a sound dampening box for a vacuum pump. It’s loud almost 96dB. I have an ultra quiet fan to vent heat out of the box. I want to calculate how to make a couple small inlet holes while ...
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### Why does the density decrease equal the speed gain at Mach 1?

In this answer, it says : "At small Mach numbers, changes in speed cause negligible changes in density, but as Mach approaches unity, both are of similar magnitude. With Ma>>1 , changes in ...
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### Does air gap between enclosed chamber and manometer influence the manometer reading?

We have an enclosed chamber filled with water. From the top of the chamber there is a metallic tube connecting the chamber to a monometer. We increase the pressure of the water inside the chamber buy ...
1 vote
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### Is there a way of changing air refractivity?

Is there any kind of way/equipment that can change the air refractive index? For example, a mirage is hot air refracting light in a certain way, making it look like water. The best I could think of ...
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### How to maximise air flow in a pipe?

I have a pump provinging a constant airflow through a pipe with a diameter of 3 milimeters. The pipe will then Go trhough a larger pipe with a diameter of 11 milimeters. I have the possibility to ...
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### Funneling air into a small opening, calculating time of speed differential

Assume I have a funnel that fits a rectangle air vent of 1" x 4" with an opening for a circular tube of 0.5" diameter. After connecting a 0.5" diameter x 2 ft tube to the funnel, ...
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### Does food stay hotter if you keep air in the bag?

If I am taking takeout home in a plastic bag, is it better to remove all air from the bag when sealing it so no heat is lost to the surrounding air or keep air in the bag acting effectively like ...
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### How carbon water filter can build air pressure inside (before installation)? [closed]

Today I got a new refrigerator carbon water filter. Before installing, out of curiosity, I dripped a bit water into the filter’s outlet to see if water could flow in and out. Obviously it did… Then, ...
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### Will hot object near ceiling vent create more draft? [closed]

As in the picture, we have a room with vents at the bottom to let cold air in and at the top to let hot air out. Normally the air flow is limited by the temperature gradient (correct me if I'm wrong). ...
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### What does a dynamic-pressure loss coefficient of more than 1 mean (for eg air going through bend)?

Air flow (eg in a duct) has a dynamic pressure, and when the air flow goes through e.g. a 90°-bend the bend has a dynamic-loss-coefficient. The dynamic-loss-coefficient is used to calculate the total-...
1 vote
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### Does air pressure change at the same rate on high elevation land as in the sky? [closed]

Is air pressure the same in a place like Denver, which is a mile (1.6 km) above sea level, as the same elevation above actual sea level? Same question for 2 miles high, as in any number of mountain ...
1 vote
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### Formula of cooling power of compressed air [closed]

For my blog on Trompe air compressors I am looking into uses that people could have with these compressors if they build one themselves (for big versions see this Ragged Chute Trompe). One of the uses ...
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### Why does blowing air on wet bodies dry it? [duplicate]

Suppose I blow dry a region with some water on it. Would it dry it faster than otherwise? If yes, why? I can give one qualitative reason against it, since the blow dryer is blowing room temperature ...
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### Does a planet's "equatorial bulge" induce any kind of motions or currents in the atmosphere?

Rotating planets, like the Earth, are not perfect spheres but are instead oblates. This affects both the crust and the atmosphere, creating a bulge in the equator 1. I was wondering if there are ...
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### How much deviation from ideal gas does the air in a 'Room' show?

First of all, I'm only concerned about air in a Room (room in our houses). Also, lets take room temperature to be $27^{\circ}$ C specifically. My first question is, how much different is this gas (air ...
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### What path will air take to leave the space station?

Hi everyone, lets say we have a circle shaped space station and there was an accident where we got a hole (hole A on the picture) on a station and now most of the station is vacuum except for one ...
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### Does EM wave lose energy in air?

Light is EM wave. As it travels through vacuum, it does not lose energy but I am wondering if it travels in air, just imagine light in your home. Before it reaches your eye, it has to travel through ...
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### Would an adhesive surface have more air resistance?

Imagine spreading double-sticky tape all over the surface of a car or a plane. Would there more significantly more aerodynamic drag as a result of the adhesive 'sticking' to air molecules and slowing ...
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### What part of my oven should be hottest, top or bottom? [closed]

My oven has the heating element in the bottom. So the bottom shelf is more directly exposed to it, and should be the hottest shelf. But hot air rises, so the top shelf should have the hottest air, and ...
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### What is the physical reason for why hot air holds more water vapour, and how does this relate to saturation vapour pressure?

It is said that hot air holds more water vapour. I guess this means that the saturation vapour pressure of water in air increases with temperature. Is this correct? How can one derive this result? ...
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### Airflow between two rooms (one hot, one cold) [closed]

Scenario — It is night time and somewhat cold outside. Room 1 (Bedroom): The window is slightly creaked open. I have a space heater going on continually heating room 1. One door is closed to the ...
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### Lift and drag forces in parachuting

EDIT: guys, I am not a physicist and it is not my study field, So even if you see my question is silly to be answered, I hope you can give me a clue. I hope you are doing well. I have some questions, ...
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### How can I mathematically model the entrainment of air through a window?

The Problem Suppose I have an open window with an area $A$, and a uniform wind source (a fan) pointing towards the window, positioned at a distance $s$ away from the window. At the exit of the fan, ...
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### Is the sound from a chimney fire the same as the sound caused by a fire inside a fireplace?

For a while now I've been researching the causes of why a fireplace fire makes a roaring sound, and from what I've read, it mostly has to do with the way air rises, creating a vacuum underneath, ...
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### Does the earth exert centrifugal force on us in air? [closed]

Whether the centrifugal force exerted by earth due to rotation be felt or even applied to us if we were in air ? The landmass rotates with earth so it is exerted on us radially outwards , but that isn'...
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### Why does blowing a whistle in someone's ear damage it more than blowing directly in their ear? Won't the whistle reduce overall energy?

If I blow really hard from a whistle near someone's ear, it'll hurt a lot. But if I blow directly at a person's ear, it won't hurt nearly as much. But shouldn't the whistle (or any other obstruction) ...
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### Is there any physical explanation for negative extinction coefficient, $k(E)$, over a spectral range of energies?
Measured data for $n(E)$ of air were fitted to equations for $n(E)$ and $k(E)$. The measured data for n(E) spanned 0.734 to 6.702 eV. To obtain fits to the equations for n(E) and k(E) in the absence ...