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

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If a super massive black hole captures a very small black hole, would the smaller black hole be immune to spaghettification?

I think to answer this question we would have to fully understand the nature of black holes. It seems to me that the smaller black hole could have a lower density than the larger one. In this case the ...
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How can a singularity have infinite density? [duplicate]

I've heard many times that black holes have infinite density at their center, but I've also heard astronomers quote mass estimates for black holes. How could the singularity have infinite density if ...
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Is density of an element directly proportional to atomic number or atomic weight? [duplicate]

Is the density of an element directly proportional to any power/order of atomic weight or atomic number? I know very less, probably only highschool level physics, after which my brain has been ...
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Density and pressure of the earth core [duplicate]

According to some sources the density of the earth core is about 9.5kg / m^3 and the pressure: 4*10^11 Pa I know the gravitational force decreases, if you get closer the center of the earth, ...
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48 views

Disc and hole - moment of inertia [closed]

Determine the moment of inertia of a homogeneous disc with density $\rho_0$ of radius R with a circular hole of radius R/2 and central radius R/2 regarding an axis perpendicular to the surface and ...
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Why are densities not fields?

I have read (in Statistical mechanics of lattice system 2: exact, series and renormalization group methods by D.A. Lavis and G.M. Bell pg 2 ), that intrinsic variables are either fields or densities. ...
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What exactly is a one particle density?

In Density Functional Theory (DFT) we derive the Grand Potential as a functional of a so-called one particle density (OPD). I have trouble imagining what exactly that is. Could someone help me with ...
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Why is it difficult to mix helium and nitrogen gases?

I recently learned an interesting fact: That it's difficult to mix helium and nitrogen gases in a compressed gas cylinder. Gas suppliers that need to mix the two gases have to rotate the cylinders for ...
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As the speed of sound varies in different mediums, what's the density of a theoretical material that allows it to go at the speed of light? [duplicate]

Viewing a list of the speeds of sound in various mediums, I note that none of them come even close to 300,000,000 m/s. It appears that as the speed of sound goes up, the object's density more or less ...
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68 views

Are atoms compressible?

Liquids are not compressible, but what does compressible mean? Does it mean the increase in the density or decrease in volume? Or something else? Why are liquids incompressible, in a way nothing ...
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22 views

An example on computing the density of a typical nucleus

An example from my text is as such: Compute the density of a typical nucleus, and find the resultant mass if we could manufacture a nucleus with a radius of 1cm. I will only provide a partial ...
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338 views

How does one write density as a form?

In vector calculus, given the density $\rho$ of a body with volume $V$, it's total mass $M$ is simply $M=\int_V \rho dV$. If density $\rho$ is a form, say dm it would need to be a volume form to ...
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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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Meaning of negative density

Charge density depends on the area/volume and the amount of charge. Before electromagnetism I used to think of density as being positive only. What is the intuitive meaning of negative density? Does ...
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35 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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98 views

Why can liquid mercury sit on salt?

A video shows liquid mercury sitting on top of table salt. Even though the mercury is much denser, it does not sink to the bottom. Why does this happen? Is the mercury just so thick that it is like ...
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41 views

Will this balloon rise?

A helium balloon contains mostly helium which is an inert gas that is less dense than the air around it, suppose I drained all the air molecules from the balloon and note that this special balloon can ...
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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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64 views

Speed of sound in an inifinitely dense medium

Curious thought i just had. The speed of sound is affected by a few factors, but the density plays a large role. As density increases, does this mean that sound could approach the speed of light? If ...
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69 views

Schwarzschild radius in black hole density

The textbook from which I teach physics at the end of secondary school has a question about the density of a non-rotating black hole. Because the density at the singularity is perhaps infinite or ...
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51 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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49 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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1answer
25 views

Is density of a material related to penetration?

Theoretical question. If you have a standard projectile with mass 1 and velocity 1 and fired it at different materials would the penetration be related to the density of the material? I'm not trying ...
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Calculating charge density

When calculating uniform charge density, I yielded a solution with units: $$VC^2 / Nm^2$$ The answer is telling me that this is equivalent to: $$C/m^2$$ where: $$m : meter$$ $$C : Coulomb$$ $$V : ...
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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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How does water pressure manifest itself on the molecular level?

Second, related question: does water density relate to, or cause, water pressure? Everyone I talk to dismisses the idea that water density substantially affects pressure, and emphasizes that water is ...
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2 different density liquids in space

Lets say you are in deep space with basically zero gravity. You have a ball of water floating in front of you. If you carefully injected that ball with a syringe filled with vegetable oil, what ...
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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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Will water in an oil-filled jar sink or float?

If I pour a spoon of oil on a jar full of water no doubt it will float. But if I were to pour a spoon of water on a jar full of oil would it sink? Why or why not?
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637 views

Does increasing the tension on a string also increase the density?

Consider a string under tension, for example, a string on a guitar. When a guitar string is plucked, it vibrates at a certain frequency. When the tension on the string is increased by twisting the ...
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135 views

If we dropped an object into the Pacific Ocean, would it completely sink to the bottom of the ocean floor or not?

Obviously if the density of the object is smaller than the density of water it would not sink at all. But I was thinking that, even if the density of the object is greater than the density of water, ...
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How do you calculate density if you also account for gravity?

Consider this. I have an Earth-sized quantity of water that I throw into space. Naturally, it will assume the shape of a ball. Now hear me out. Density's definition generally assumes that it will ...
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Why aren't all black holes the same “size”?

The center of a black hole is a singularity. By definition, a singularity has infinite density. So how can a black hole with a different mass or density be described?
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Probability flux: spatial variation of the phase equal to momentum?

We can write any wave function as $$\psi(\vec x, t) = \sqrt{\rho(\vec x,t)}\exp{\left[\frac{iS(\vec x,t)}{\hbar}\right]}$$ for $S$ real and $\rho >0$. Here we interpret $\rho$ as the probability ...
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How can a gas giant be about the same size but six times more massive than Jupiter?

I've just read this article: http://www.sci-news.com/astronomy/science-kepler-432b-new-super-jupiter-exoplanet-02490.html And I wondered how this could be possible? Maybe it's because this gas giant ...
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52 views

Relationship between energy density and energy flux

I'm presently working on obtaining conservation laws via symmetries. These conservation laws are written as 2-element vectors where each element is the energy density and energy flux. To proceed in my ...
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382 views

Why does a metal boat float?

I was in class learning about density and stuff. Our teacher told us that things that are denser than water sink in water, and less dense things float. Then, our teacher asked us why metal boats ...
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Longitudinal Waves - how velocity varies with density

The formula for finding the velocity of a longitudinal wave, such as a sound wave, is: $$v = \sqrt{\frac{E}{\rho}}$$ Where $v$ represents the velocity, $E$ represents the elasticity of the medium, and ...
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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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622 views

Relationship between electrical resistivity and density

I just read this answer on EE.SE and that triggered a doubt in me. If I were asked whether there is any relationship between the electrical resistivity and the density of a substance I'd answer ...
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Strange Airy Black Hole

Imagine a sphere, with a radius about the size of the Solar system. Somehow fill it with air at 100KPa (Earth surface density). $1 km^3$ of air is about 1.25 billion kg. A Solar system radius is about ...
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Two superimposed sounds traveling through low- and high-density matter: is separation possible?

Two superimposed sounds (at source: $s(t) = s_1(t) + s_2(t)$; the two sound components overlap completely in time, partially in spectra) travel through low- and high-density matter and are recorded ...
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Can the density of quarks be more than density of black hole? [duplicate]

I have found this list of densities here: http://wiki.chemprime.chemeddl.org/index.php/Density_of_Black_Holes and I am looking for the density of quarks but I have not found it. I was wondering if ...
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Can a star with a constant density profile be possible?

The equation of states for a star is given by a polytropic equation, where density depends on the $n$th power of $\theta$. Please refer to the literature First, what is this $\theta$? It can't be a ...
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floating human on gas experiment

http://m.youtube.com/watch?v=DzLX96VWTkc&feature=youtu.be I saw this and now I' m wonder is it possible to make this gas to lift human . I read thread about making air dense as water and it is ...
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What is the definition of density in a relativistic context?

In this question, there seems to be a clear presence of ambiguity, which raises the question: what is density in relativity? First of all, the question asks for the relativistic mass, "the apparent ...
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70 views

What should density of water be to keep box afloat?

I'm writing a platformer game and my physics engine is Box2D. I have successfully implemented buoyancy, but have a question about mass and density. My player is 80kg, a box has a density of 0.5 and ...
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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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Density of a planet

I was wondering, how would you find out about the mass and the density of a planet and what the planet is made of? Finding out about the mass might be possible, because you can observe the movements ...
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Why does iron sink in molten iron instead of floating?

Why does iron sink in molten iron whereas ice floats on water? Both are solid states of their own form, so why is one floating and the other sinking?