Density is defined as the mass per unit volume of a substance.

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Separation by density

How can i separate water vapour from a mixture of gases given that water vapour has a lower density than the gases? I am doing an experiment on separating water vapour from exhaust gases. I have not ...
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321 views

Does tunneling transmission probability depend on the density of states or velocity?

In some quantum text books [1], the tunneling transmission formula depends only on the density of states of 2 regions (DOS) involved in tunneling. ($T(E) = C \times DOS_1(E) \times DOS_2(E)$, where C ...
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47 views

Suffocation in a granular medium

I read of a recent accident in Alberta in which three girls fell into an open bed truck carrying canola seeds and suffocated. In that situation would it have been possible to keep breathing by using ...
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178 views

Physical Significance of the Planck Density

The Planck density is the Planck mass devided by the Planck volume, approximately 1093 g/cm3. Does this quantity have any known physical relevance? The Planck mass is believed to be the smallest ...
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25 views

Compute affect of a shower on density altitude

As a pilot I have a basic understanding of density altitude, how temperature affects the effective air pressure: I noticed recently that I have difficulty breathing when I take a shower in Santa ...
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1answer
29 views

Reference values for viscosity and density in incompressible NSE

I come from a pure mathematics background, so I have very limited physics knowledge. I'm currently working out the non-dimensional form for the Navier-Stokes equations and have some questions. Where ...
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1answer
67 views

What is the highest density to be measured?

In the abstract of the recent article named "Transport properties and equation of state for HCNO mixtures in and beyond the warm dense matter regime" we can read that authors measured a density of ...
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50 views

Density depletion for Fermions

In my recent advanced statistical physics class, I read about the density depletion of Fermions, which are "defending" a given volume around them against other Fermions, while the exchange hole ...
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1answer
21 views

How are homogeneity or heterogeneity of materials decided?

How is the homogeneity or heterogeneity of materials decided? What kind of measurement or assessment exists for inferring when e.g. the density of the material of an object is uniform across the ...
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What special significance does the eigendecomposition of a mixed density operator hold over other pure state decompositions?

It is known that in general, a mixed state can have multiple pure state decompositions. However, it has a unique eigendecomposition in the absence of degenerate eigenvalues. What is the special ...
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304 views

Packing Fraction vs. Packing Density

Hello: I am confused if Packing fraction and packing density mean the same thing. I have been led to believe they are different. I would like help in sorting the confusion. Thanks. Also is packing ...
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420 views

How to calculate flux density in a toroidal CT that has an electrical line pass through the center?

I have seen the Biot–Savart equation, but I don't know how to apply it. Does the conductor length need to be considered finite and equal to the core length, or will the calculation be for a conductor ...
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177 views

Density of states and fermi energy

I am trying to find the fermi energy and density of states. From the equation: K_F^3=3*(pi)^2*n and n=NAvagadrosdensity/m what is the big N here?
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Is there a material with non-monotone density dependence on pressure?

Is there a material with such non-linear effects (including chemical reactions, phase transitions etc ...) so that there would be range where pressure increase would yield density decrease? What ...
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Charge distribution and potential in a 1-dimensional quasistatic system

Suppose you have an 1-dimensional system with a charge distribution $\rho(x)$ (not given) moving with an speed $v(x)$ (not given), calculate the potential $\phi(x)$ and the charge distribution ...
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In the αβγ cosmology paper, how do the authors assume the integral of density over time in the early universe?

In the famous Alpher-Bethe-Gamow paper, the authors say: "it is necessary to assume the integral of $\sigma_n dt$ during the building-up period is equal to $5 \times 10^4 \frac{\text{g ...
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How did Lord Rayleigh find the volume fraction of argon to air?

In order to isolate for pure nitrogen, Lord Rayleigh and his colleagues took some air and removed oxygen, carbon dioxide, and water vapour, leaving behind what he believed to be pure nitrogen. In ...
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Modelling gravitational potential of a galaxy

I am interested in modelling the gravitational potential of a disc-shaped galaxy with radius $R$, i.e. solving the 2D Poisson equation numerically by Gauss-Seidel relaxation: $$\nabla^2 \phi = 4\pi G ...
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What are the physical limitations on energy density for a useful, safe battery, and are we anywhere near them?

Energy storage seems to be a fairly major bottle neck in technological development at the moment, especially for important things like clean-energy powered transport, but also for consumer goods. Are ...
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Are densities only good approximations?

In a number of situations, continuous densities (e.g. for mass, electric charge, etc.) are used in calculations. However, for example, as far as I know, matter is not continuous. Also, for example, ...
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68 views

Mass, density and gravity for 2D SPH

Having previously only worked with 3D sph, the 2d case is confusing me. The concept of mass and density as well as gravity is not easily converted, as I see it. As an example in 3D I take 1000 ...
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52 views

Energy density question

I have looked for these formulas everywhere but cant seem to find them... What is the formula for the energy density of the electric current ,and the energy density of the mechanical wave?
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What is the difference between antiferromagnetism and spin density wave?

It seems that antiferromagnetism can be treated as a special case of spin density wave with wavelength equals to twice of the unit cell. Is that so?
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Distribution of refractive index of water when applied pressure wave

I was wondering when applying pressure wave, ultrasonic sound waves, under water, how I would be able to measure the distribution of the refractive index.
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Determine the particle velocity of a pressure wave

I am using constant density wave propagators to model seismic waves in the subsurface. What I want with these acoustic waves is to estimate the energy of them at a certain grid point at a given time. ...
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Nucleon-nucleon collision density

Can someone help me derive expression for nucleon-nucleon collision density as a function of transverse plane coordinates (ultra-relativistic heavy ion collisions) using Wood-Saxon nuclear densities( ...
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Why does individual N2 molecule rise when heated?

I get that hot air is less dense so it rises due to floatation and all, but what happens to one individual diatomic Nitrogen that it increases it's distance from ground? And why is it that the air is ...
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How can I estimate the density of non-ideal vapor mixtures

I am trying to estimate the density of a non-ideal gas mixture and can't seem to find any resources for how to go about this. For some gas pairs like ammonia-water there are empirical correlations ...
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107 views

How do we measure mass distribution in an object?

Given an object I want to know the mass distribution among different section. What are the inexpensive methods to know this ?
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74 views

How much water is needed for Saturn to float in?

Saturn floats because it's density is less than that of water. Just how much water would be needed? Assume a cuboid tank holding it. And when we actually put saturn in that water, how far in the ...
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75 views

Why is the matrix representation in the same basis not same for a density operator?

I have a $\rho : V \to V$ density operator of a $n$ dimensional space $V$ and $\{i\}=\{i_1,i_2..i_n\}$ is an orthonormal basis of this space. The density operator is defined as $$\rho=\sum ...
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52 views

How long did it take for the universe to become 1 one light year?

Given the density, pressure and other cosmological parameters. At this point we're not even thinking of time... But would this have occurred during or post Inflation? Could this be the Expansion ...
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47 views

Milky Way Density Profile

Does anyone know where I can find either a printed version or, better, a downloadable dump of data giving me the density profile of the Milky Way? I'm looking to put together a quick-and-dirty ...
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52 views

What happens when electromagnetically shunken coin is heated

The question is simple: What happens to coin/object that was electromagnetically shrunken by a coin crusher device is then heated until it (I asume) melts? Do I have misconception or not just ...
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concept of density in gravitational lensing

I may just be being very dense (no pun intended) but i'm reading up on gravitational lensing and it seems to require a notion of density (e.g. see here) I'm working on a question involving light ...
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316 views

Acting on a current density operator in second quantization

I have a current density operator in second quantization in the form: $\hat{J} = -i\left(\psi^\dagger \partial_x \psi - (\partial_x \psi^\dagger) \psi \right) $ operating on some state: $|\phi ...
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What is the electrical field of a capacitor plate as a charge approaches

The electrical field for a charge density $\varrho(r)$ is $${\bf E}({\bf r})=\frac{1}{4\pi\varepsilon_0}\int \varrho({\bf r}')\frac{{\bf r}-{\bf r}'}{\hspace{.1cm }|{\bf r}-{\bf r}'|^3} \mathrm ...