# Tag Info

11

The relative humidity of air is pressure dependent. Your method of popping your ears involves increasing the pressure of the air in your mouth. And if you sufficiently compress a volume of air that has a high relative humidity, you can increase the air's relative humidity beyond it's saturation limit, which causes the water vapor in the air to start to ...

10

Very interesting observation. I think what you are observing when your mouth is away from the tube is MORE than just the air you exhale - because the air in the vicinity of your breath is being "dragged along" by something called "entrainment". This is the principle behind an ingenious fan, called the Dyson Air Multiplier: A detailed explanation of how it ...

4

The front of the train compresses air which can blow you away, while at the back of the train air rushes back in after the train has displaced it. This backdraft is especially troublesome in closed areas such as subways, where a train exits a small tunnel near a platform and the displaced air rushes back into the vacated tunnel. Next time you see a big truck ...

4

No, there is no contribution to the pressure from the gravitational attraction between the particles. To see this you need to appreciate that the pressure is an ensemble property, and look at the stress-energy tensor for a single point particle. This is: $$T^{\alpha\beta}({\bf x},t) = \gamma m v^\alpha v^\beta \delta\left( x - x_p(t) \right)$$ where $v$ ...

3

Any kind of "funnel" - an area where tall buildings create an obstacle to the free flow of air - acts as an amplifier to wind. That is, even a little bit of air moving from point A to point B will notice the "obstacle" that is a pair of buildings; it will build up pressure in front of the buildings and result in a faster flow of air through the passage. An ...

3

This phenomenon has been well-researched. If the underground pipe is almost full with rapidly-flowing water the waves in the pipe will cause the pipe to be completely filled in some places. The waves are irregular and the air in between the wave crests gets compressed - when it passes the manhole access the air is vented. 1000Pa is actually a very small ...

2

First and foremost, a primer over what "buoyancy" is is needed. Pressure decreases with altitude. The atmospheric pressure at the top of the balloon is a tiny bit less than the atmospheric pressure at the bottom of the balloon. This pressure difference results in a tiny net upward force on the balloon. The balloon rises if this tiny net upward force exceeds ...

2

As mentioned in the other answer, additional air is being entrained. This principle can be used to produce considerable flows and considerable pressure differences. Examples In a steam locomotive, the exhaust steam from the cylinders is directed to a nozzle that points upwards towards the exit of the funnel. This draws the smoke through the boiler and ...

2

I think there is a difference between the amount of pressure exerted on a flat surface by the fluid in a wind tunnel versus the amount of pressure that makes down your ear canal to your ear drum. The wind in a wind tunnel is not directly incident on your ear drum. I imagine if one could directly apply a 15 m/s flow onto the ear drum, it would hurt. ...

2

When the cap bursts off the bottle the air inside it will expand rapidly and adiabatically, so its temperature will fall. If there is enough water vapour in the air inside the bottle, and if the temperature reduction takes the temperature below the dew point, the water vapour will condense giving the fine mist that you see. In this case it looks to me (it's ...

2

The rotation is part of the key to the storm itself. Primarily the pressure and temperature differences are what causes these systems to take the shape and forms that they do. Once a tropical depression starts to form you can already see rotation in the moisture around the low pressure zone, even through it typically looks nothing like a hurricane. Not ...

2

Yes you are right. The 10kg piston acts as a force over the area of the piston, increasing the pressure and decreasing the volume of the gas inside. When the set up is tilted, the force no longer acts on the gas, but sideways, so the pressure equalizes.

2

The jumping manhole lid caused by the Bernoulli`s principle sounds quite reasonable at the first glance. However, I have seen a few storms in my life, but no jumping manhole covers that I can recall. Also, I noticed, that in the video the jumping does not match the wind gusts (observe that small tree). In the absence of trolling sewer workers, the lid ...

1

One could probably measure the light pressure of a photon gas on a pair of parallel mirrors. Experimentally that's on the order of 1e20+ particles in a relatively small setup with two dielectric mirrors and a laser. The resulting force should be around 1e-7N, which is easily measurable. Would you accept that as an implementation, or are you looking for an ...

1

Usually it's not quite true that there is no regulator - typically these types of cylinders have a pressure reduction valve that doesn't look like much. There's nothing to "regulate" but they reduce the pressure from 100+ bar to something that makes sense for filling balloons. A similar thing is used in scuba diving: the "primary regulator" takes the ...

1

For aviation purposes, standard atmosphere is considered to be dry air at mean sea level, at 15 degrees C (59F). It is true that pressure decreases with increasing altitude, and temperature usually does, but not always. It is not a simple relationship, because it depends on humidity, heat transfer from above and below, vertical circulation, horizontal ...

1

Why can't we measure the pressure at 1000 m for different temperatures? Meteorologists certainly can do that, and in fact do do that, all the time. They use weather balloons, sounding rockets, and all other kinds of instrumentation to measure conditions in the atmosphere. The resulting picture is rather complex. Conditions vary with place, the seasons, ...

1

I can only assume that 25 cm of vacuum refers to a vacuum which is at 25 cmHg of pressure. I do think going down to 25 cmHg would mean ~33,330 Pa; that's within the range of a low vacuum.

1

There's static pressure (P) and dynamic pressure ($\frac{1}{2} \rho v^2$). A pitot tube placed in the center section of your drawing will measure the stagnation pressure, which is the sum of the two terms. Physically, the dynamic pressure will be larger at the narrow section, and the static pressure will be smaller there. The sum will be constant ...

1

Like any object moving through a fluid, a high-speed train distorts the air as it moves through it. Broadly speaking, there are three main regions of flow structure around a high-speed train: the upstream distortion, boundary layer and wake. These can be collectively referred to as the slipstream. The effects of the slipstream on a static observer (e.g. a ...

1

Well this happens mainly due to two factors- The pressure difference inside the drain and outside. there is high pressure inside the drain which is balanced by lifting the lid. The excessive increase in water level in the drain. These two factors result in the water gushing out after the air from the air gaps come out. This may also happen due to ...

1

I know that air pressure and temperature are inversely proportional. You should not know that. This is the source of your misunderstanding. The ideal gas law, $PV=nRT$, can be rewritten as $P=\frac R m \rho T$, where $m$ is the average mass of a molecule in the gas and $\rho$ is the density of the gas. The first term on the right is a constant for a ...

1

All first order phase transitions have a change of volume. With different pressures you need to consider the sign of the work $P\Delta V$ that needs to occur during the phase change. If $\Delta V$ is positive, the phase change will occur at a higher temperature for higher pressure. If negative, the phase change will occur at a lower temperature. (Note ...

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