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

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Density of the universe [on hold]

Why is the universe of the same uniform density at all distance and time scales? Why haven't cosmologists realised this simple fact disproves the big bang? Why do they keep pushing theories as ...
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Metal surface density increase [on hold]

Can you increase the density of a material surface (metal) by surface treatment? For example commercial copper. If we take the ordinary OF copper (99.95%), I would expect not to have the tabulated ...
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462 views

When Sugar Is Added to Water, How Does the Mass Change, and How does That Affect the Water's Density and Boiling Point?

I can't find a good answer anywhere. How does the amount of sugar added change the boiling point, mass, and density of water? Does it affect the mass or the volume? Or both?
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Consequences of general equation of hydrostatics $\nabla p= -\rho \nabla E$ in terms of surfaces where $p$ and $E$ are constant

I'm facing difficulties in understanding the consequences of the general equation of Hydrostatics in the case of conservative forces. $$\nabla p= -\rho \nabla E\tag{1}$$ Where $p$ is the pressure, ...
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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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Speed of Sound in matter

So basically when it comes to the speed of sound, it is said that speed of sound in media is based on two main factors - 1)elasticity and 2)density from the formula V= $\sqrt{E/\rho }$ where E is ...
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Finding density using bulk stress equation

Basically, I'm using the equation $\frac{F}{A} = -B\times \frac{\bigtriangleup V}{V_o} $. Originally I had to find the change in volume given an initial volume (B and pressure ($\frac{F}{A}$) were ...
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Do glass panes become thicker at the bottom over time?

Is it true that a glass window, that has been placed in a wall for about 10 years or more, is thicker on the bottom than on the top? I can vaguely remember my physics teacher saying that this was ...
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0answers
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Conversion from PPBV to PPBM [closed]

What is the conversion between PPBV and PPBM? I have a database that includes values of Parts-per-billion-by-volume (PPBV) as a function of altitude. I've been asked to convert this to ...
0
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1answer
474 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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876 views

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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2answers
90 views

Using $\sqrt{-g}$ in integrals of proper volume

I am a little confused over integration using proper volume element. When do we use $\sqrt{-g}$ in calculations? For example, in many calculations involving stars, say when using TOV equation, this ...
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4answers
272 views

Do hail stone fall down just when it is created?

Density of ice is much higher than air. Then how can hail stone remain in earth atmosphere before they fall down ?
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1answer
36 views

Atmospheric pressure question [closed]

I'm asked to find at what altitude atmospheric pressure falls to 10% of the mean sea level value. I have found the expression for the variation of pressure with altitude to be $$p = p_0e^{-h \over ...
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2answers
44 views

Approximating Gas Density

So this was a random thought I had that I thought would be fun to mess around with using an Arduino and some sensors, but after the difficulty I've had I'm just curious to see if it can be done at ...
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6answers
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How can super massive black holes have a lower density than water?

I heard on a podcast recently that the supermassive black holes at the centre of some galaxies could have densities less than water, so in theory, they could float on the substance they were gobbling ...
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3answers
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How can black holes be so dense?

It is said that if the Earth were a black hole, it would be the size of a peanut!? How is this density possible, are atoms really that sparse that they can be compressed so tightly? Is there some ...
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3answers
296 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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2answers
36 views

Density of air using ideal gas law

I need to find the density of air using (I think) the ideal gas law. I have calculated $V$ of an ideal gas at s.t.p. to be $.0224m^3$. I am asked to find the density of air knowing it's temperature ...
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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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2answers
63 views

How much Oxygen is in ζ-phase metallic Oxygen?

I am playing with a sci-fi idea of Oxygen storage for breathing. I wonder how do some compressed forms of Oxygen compare to human-breath-Oxygen (room temperature, room pressure) in terms of density. ...
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4answers
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Why does squeezing a water bottle make the water come out?

This seems natural, but I can't wrap my head around it when I think about it. When I squeeze an open bottle filled with water, the water will spill out. When I squeeze a bottle, the material ...
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Does the mass of a star change as it collapses into a black hole?

I know (I think!) that when a really big star collapses on itself it creates a black hole. My question: When a star collapses, is the mass equal to the mass of the star when it's not a black hole? Or ...
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Where does an object with density lower than outer space go?

Assume there was an object with lower density than that of the interstellar medium (which is extremely low already at just a few particles per cubic meter). If that object were released on Earth, ...
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Besides water, which substances are less dense as solids than as liquids?

You can read everywhere about water's extraordinary property of expanding when frozen, thus the reason ice floats on liquid water. What other substances do this? There are claims of mercury, silica, ...
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Pressure question problem in forming the equation

A tank contains sea water of density $1030 \frac{kg}{m^3}$ The pressure at point M is $60 kPa$ more than atmospheric pressure. Calculate the depth of M below the surface of the water. My attempt: ...
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Are black holes very dense matter or empty?

The popular description of black holes, especially outside the academia, is that they are highly dense objects; so dense that even light (as particle or as waves) cannot escape it once it falls inside ...
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How does air density affect corona discharge?

I'm wondering how local air pressure and density affect the amount of ionizations occurring in a corona discharge. Also, does the threshold voltage required for a corona discharge vary with air ...
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2answers
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What would happen to a teaspoon of neutron star material if released on Earth?

I've read on NASA's page on neutron star that one teaspoonful of that star would weigh over 20 billion tonnes on Earth. If it was somehow possible to bring it to earth would it: Burn and disappear ...
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1answer
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Explanation for concept of Relative Density

I am in class $9^{th}$, I'm reading my physics book in which it is written that: $$\mathrm{Relative\ Density} = \frac{\mathrm{Weight\ of\ solid\ in\ air}}{\mathrm{Loss\ of\ weight\ of\ solid\ in\ ...
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Density solver for ideal mixture of real gases

I am referring the paper on GERG-2008 equation of state. I am interested in calculating the properties of ideal mixtures of real gases. The GERG-2008 EOS is in Helmholtz free energy and hence the ...
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4answers
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Alternative liquid for Galileo thermometer

So a friend of mine broke my Galileo thermometer recently. The glass tube and the liquid inside were lost, but the bulbs survived. I've cleaned out an old tall glass candle, and tried filling it with ...
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If there were a planet with oceans tall enough saturn fitted in, would it be floating around? [closed]

In this morning I read an article that claimed (translated into english, so emphasis mine) Saturn is so slight1 it would float around in an ocean. So appart the missleading wording of its ...
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Standing Waves in a String of two Linear Densities

Given a string with sections of two linear densities like this: Does the point where the two linear densities meet have to be a node if a standing wave is produced? Are there alternatives? Could I ...
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1answer
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Does matter found at densities of white dwarfs “feel” more like a solid, liquid or gas?

I'm wondering what it would be like to touch or interact with very dense degenerate matter like this found at white dwarfs. I understand that white dwarfs are initially very hot, but for the sake of ...
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1answer
239 views

Is there a charge density in quantum mechanics?

Is it meaningful in quantum mechanics to speak of charge distribution? Some people say if you sovle the Schroedinger Equation for the hydrogen atom, the eigenfunctions represent a type of charge ...
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1answer
65 views

How does the gravitational field behave inside a star?

The interior gravitational field of a star with constant density is given by ...
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1answer
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Deriving a diffusion equation from a given mass flux density [closed]

I am given that the mass flux density $q$ of a substance in a medium obeys the following physical law. $$q=-D\frac{n^3}{n-n_0}\frac{\partial n}{\partial x}+nv,$$ where $n(x,t)$ is the ...
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2answers
56 views

Confused about volume, density and mass, help!

I got into an argument with my friend, which cast confusion on my understanding of density and its relationship to volume. I'm hoping to get some clarity. The argument involved describing density in ...
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1answer
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Is there anything special about the Sun's photosphere in terms of density?

The Earth has a definite boundary between rocky/ watery surface and gaseous atmosphere. The same cannot be said of the sun. Even though the photosphere gives an apparent "edge" to the sun via the ...
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2answers
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What's the nature of intraction between hydrogen atoms in the interstellar medium?

Interstellar densities are about 1 atom/cm$^3$. Do these atoms even move? If they do, why do they move? What would be their average speed? (Free expansion)
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12answers
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Does hot air really rise?

"Heat rises" or "warm air rises" is a widely used phrase (and widely accepted phenomenon). Does hot air really rise? Or is it simply displaced by colder (denser) air pulled down by gravity?
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1answer
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Is it easier or harder to move moist air with a fan?

From what I understand, the molecular weight of water is lower than the molecular weight of nitrogen and oxygen. So, shouldn't it be easier for a fan to move moist air than dry air of the same ...
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1answer
485 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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Is there a limit to the concentration of photons in a given volume?

If you have a given fixed volume, is there some physical limit to how many photons can exist in that volume?
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5answers
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What makes water heavier than air?

I apologize in advance if this is too basic for this site. Considering that hydrogen is lighter then oxygen, and water is 2/3 hydrogen, and only 1/3 oxygen, and our "air" is comprised mainly of ...
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1answer
51 views

Is there a limit to the size of black hole?

I have read answer by @John Rennie in regards to the size and density of black hole. In the last sentence he states that super supermassive black hole ...
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Changing the Density of a liquid while its surface tension is constant

I'm working on Plateau-Rayleigh waves and I want to investigate the effect of density of the liquid on the wavelength of these waves How can I change the density of the liquid while its surface ...
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How is refractive index related to the density of a medium (for example, air)?

I have a question regarding refractive index dependency on the density of a dielectric, specifically air. Background Let us start from Newton's second law form of driven harmonic oscillators ...
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Why is density an intensive property?

I am still trying to understand what are intensive and extensive properties. Possibly someone can give a pointer to a decent text (preferably on the web), as I am not too happy (to say the least) with ...