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7

Neutron degenerate matter can undergo a phase transition to a superfluid state. The process is thought to be analogous to Cooper-pairing, but the coupling interaction is of order 1 MeV, so can occur at temperatures below about $10^{9}$ K in neutron star interiors. The neutrons in the deep interior (which dominate the interior 100:1) can form a superfluid; ...


5

Sometimes I feel Wikipedia is a funny place... In the article you quote they provide a calculation from our patent application (see, e.g., http://akhmeteli.org/wp-content/uploads/2011/08/vacuum_balloons_cip.pdf ) proving that a homogeneous shell made of any existing material cannot be both light enough to float in air and strong enough to withstand ...


3

I assume you ask this because you want to know if a fart's mass contribution to body weight can be offset by its lighter-than-air property, if any. According to About.com the typical composition of human flatulence is as follows. I added the molar mass of each component, as the density of a gas determines whether it's heavier or lighter than air: ...


3

The question comes down to buoyancy: is the mass of the flatus inside the body divided by its volume less than or greater than the mass of an equal volume of atmospheric air? To answer this we need to look at the density of atmospheric air, as well as the density of flatus. Let's start with the atmosphere. We usually see the density of air quoted as 1.2 ...


3

At least in the context of ultracold atomic fermions, the answer is no. The creation of a degenerate fermi gas is, unlike a BEC, not a phase transition. One major caveat: if there is an attractive force between the fermions, one can get a BCS-like phase transition to condensation of paired fermions. This is, of course, the case for electrons in metals, as ...


2

This is the pressure-gradient term integrated over all volume, converted to a surface integral and using Gauss' theorem. Note that physicists prefer the differential form of such equations (see also this Wikipedia article), when the corresponding equation becomes $$ \frac{\text{d}\boldsymbol{u}}{\text{d} t} = \frac{\partial\boldsymbol{u}}{\partial t} + ...


1

For now, let's ignore the expansion of the container due to the heating and just focus on the stress in the wall of the pressure vessel. I will also examine the case of a thin-walled, spherical vessel, but the same procedure may be applied for other geometries. Compute Stress State First, you must compute the pressure in the walls. To do this, imagine a ...


1

Water is almost incompressable, unlike air. If you filled the bottle with air, then sent it into the Marianas Trench, then the bottle would crush until the pressure of the air inside matched that of the water outside. At that point, the bottle would be almost (but not quite) flat. If you fill the bottle with water, then the water inside cannot compress, ...


1

Atmospheric pressure has nothing to do with it as you have not created a seal. You just have more surface area and more resistance. Karate chop versus lift is just speed. If you suspended the paper (assuming it would hold its shape) on fulcrum (no surface below) you would have the same effect. Ruler alone and enough seed and you could snap it. In a pure ...


1

A few things happen. One, the paper would bend, but lets pretend it's rigid, what happens when you lift. Your assumption is correct, air moves very fast, reducing but not completely eliminating the difference in air pressure between above and below. Air (molecules) moves at about 1,000 miles per hour. http://www.phy.mtu.edu/~suits/SpeedofSound.html ...


1

Here it is an incomplete answer, but just to think about some issues. An ideal gas is assumed to have particles non-interacting and with no extension (point-like particles). In particular for an ideal gas you discard gravity. While the Stevin's law (the relation $\rho g h$) is a direct consequence of the fact that you have a fluid in a gravitational field.


1

Your answer lies in the ideal gas law: $$PV = nRT$$ where $P$ is pressure, $V$ is volume, $n$ is the amount of substance (usually in moles), $R$ is the "ideal gas" constant, and $T$ is temperature. You can see from the equation that if you're adding substance (i.e. increasing $n$), $V$ must increase proportionally (i.e. the piston must be displaced) to ...


1

There isn't a simple formula for fan noise, but the physics can be worked out from the fundamental equations of fluid mechanics and acoustics. It isn't a simple problem however. The noise created by fans is complex and from several fundamental sources, and its amplitude depends on frequency. Here is an example of a fan noise frequency spectrum for a cooling ...


1

To know the force, you'd know the area. Since Psi is a unit of pressure, you could have almost have no pressure and lift thousands of tons. On the contrary, you could have just a tiny fraction of a millionth of a gram but a very high pressure. Since pressure is defined as force per unit area, $p = \frac{F}{A} \Leftrightarrow pA = F$, the pressure needed to ...


1

The maximum change of pressure caused by a sound wave is its pressure amplitude. This would be the difference between high and low pressure areas in the sound wave. When sound is measured in pascals, however, for the purpose of computing decibels by comparing with other sounds, it's just the high pressure against the measuring surface, to the extent that ...



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