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Questions tagged [density]

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

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Derivation of pressure gradient stellar equation [duplicate]

I am trying to understand how to derive the following formula: $\frac{dP(r)}{dr}=-\frac{GM(r_<)\rho(r)}{r^2}$ The notes are as follow: Consider a star with COM and a shell: $P_1 - P_2 = -{\...
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What is the Effect of Liquid Density On Hydraulic Press Systems

Like in the title, What's the effect of liquid density we used in hydaulic press system? Does it make any difference on the force we apply to for example to lift an object? Make it easier or harder or ...
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Non-invariance of density extrema with re-parameterization

Consider a density function $f(x)$, in one dimension for simplicity. Assume that it has an extremum at $x^*$, so that $f'(x^*) = 0$. If I make a change of variables via $x = x(\xi)$, then I must ...
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Why doesn't a metre cube of common salt weigh 2170kg if the density of Nacl lattice is 2170kg/m^3?

Why doesn't a metre cube of box containing common salt weigh 2170kg if the density of Nacl lattice is 2170kg/m^3? As Mass = Volume x Density For a unit volume Shouldn't Mass= 1 x 2170= 2170 kg? What ...
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Density question [closed]

In that image apparently the graphs are true for cases at constant temperature and pressure. I agree with the first graph but I can't find an explanation to graph 2 and graph 3. I don't understand ...
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Atmospheric Density

As I was reading my textbook, I noted that it stated that the atmosphere becomes less dense as height increases. I am unable to understand this. I understand that pressure decreases as height ...
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1answer
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Why does acoustic imepdance increase when mass density and bulk modulus increaes?

If we take some material and (somehow) increase its mass density or bulk modulus then its acoustic impedance will increase as $z = \sqrt{\rho \kappa}$. That is, it What is the physical reasoning ...
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Measure liquids density: hydrometer

It is possible to measure liquids density with an hydrometer: I want to figure out how this work. Hence I wrote: $$\sum F = 0\\[1em] F_b = F_w \\[1em] \large \delta^{l}\,g\,V_h^l = m_o\,g \hspace{...
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Density of particles in the Lagrangian description of fluid flow

I am trying to learn about the material (or particle) derivative in fluid dynamics. I was looking through this explanation, and they mention things at the beginning and the end that confuse me. ...
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How can infinite density exist?

Thinking in mind, infinite density is where there is no space between particles correct me here if i'm wrong. Inside a blackhole at the core. So if there are 2 particles touching each other Then ...
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Is there a limit of maximum compaction for materials? [closed]

The question is say there is a block of steel $1\,\mathrm{m} \times 1\,\, \mathrm{m} \times 1\,\mathrm{m}$ $\left(L \times W \times H\right)$ is there a limit the material can be compressed in an ...
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gas denser than liquid [duplicate]

Theoretically, could a gas be denser than a liquid (ie of a different substance)? Does such a combination actually exist, and if so at a common temperature and pressure?
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How the matter and radiation densities of universe can be calculated? [closed]

Barbara Ryden gave somehow detailed and intuitive calculation in Article 5.1 of Introduction to Cosmology but skipped detail on some values. I don't know, it's good or not but I'm adding snaps from ...
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1answer
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What is the real definition of density? [closed]

What does density really mean? Everyone just provides me with the equation of finding density whenever I ask this question.
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38 views

At what rate does the typical human body sink in a swimming pool? [closed]

Let's say I'm $1.8\ \rm m$, $70\ \rm kg$ with a fairly typical male body shape. I hold on to the side of an otherwise normal but very deep swimming pool, then lower myself so that the top of my head ...
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If we have density and mass why should we have gravity?

In a cup filled with different solutions with different densities if we put objects of different masses they will sink to different layers ... and this can be explained by mass and density so what is ...
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2answers
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Commercially available material with highest density to cost ratio? [closed]

What are the top 5 commercially available materials (not limited to just the elements) with the highest density to cost ratio? To point to an application, say that my goal was to mass produce a solid ...
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Why do all the planets and stars in our solar system have such similar average densities?

This table lists the average density of all the planets in our solar system. We could also consider the Sun (average density 1.41 g/cm³) and Pluto (average density 1.88 g/cm³). The densest body (Earth)...
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Archimedes Principle $\Delta M$ formula

i'm trying to determine a formula for $\Delta M=M-M_{apparent}$ in terms of $\rho_o , \rho_w , M$ for a fully submerged object and I have no idea where to begin. I have attempted to draw a force ...
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1answer
63 views

Density density correlations of a simple Brownian particle [closed]

Suppose, I have a particle satisfying the equation \begin{equation} \frac{dX}{dt}=\eta(t) \end{equation} Where $\langle \eta(t)\eta(t')\rangle=\delta(t-t')$. I can now define a density like $\rho(x,...
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Salt Water Experiment [closed]

If my students pour colored water with differing levels of salinity into a clear container will the colors mix or will the water separate into different levels of salinity? THANKS!
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How do I calculate the height of a given that a bubble rises from the bottom of the lake to the top of the lake? [closed]

I am stuck on a physics problem which involves calculating the depth of a lake given that a bubble increases two times in volume as it rises from the bottom of a lake to the top of the lake. The ...
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Is $H_2O$ the only compound which has a density anomaly? [duplicate]

My question is simple: are there any elements, compounds or materials other than water ($H_2O$) which have a density anomaly characterized by a turning point in the $T-\rho$ curve?
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Should Copper 65 and Copper 63 isotopes have a larger density than a copper 29 atom?

I was looking at the first page of a paper (see https://aip.scitation.org/doi/10.1063/1.1735598#Metrics-content for details) and I ran across something odd. According to the paper, Copper isotopes 63 ...
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Does the optical density of a medium depend upon its mass density?

The optical density of a medium is quantified by its refractive index $n$. Does it have any correlation with the mass/number density of the medium? In other words is an optically denser medium must ...
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Ocean density vs atmosphere density

I understand that the density of the oceans on Earth in on average constant regardless of the depth. It is 1020 kg/m^3 at the surface and 1050 kg/m^3 at deep waters. I understand too that this is not ...
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Can ants walk on liquid mercury? [closed]

I'm not a physicist, but I was wondering: Can ants walk on dense liquid like mercury and why?
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64 views

Using Helmholtz Free Energy to Calculate Liquid Density

My objective is to find an equation of state (EoS) for density, i.e. density as a function of pressure, temperature and concentration, for aqueous acids, bases and salts. A StackExchange user ...
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63 views

Deriving group velocity from restoring force and density

I have seen that in some cases one can derive the group velocity of a wave quickly by identifying the restoring force in the system and the density of the medium that the wave is traveling through (e....
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1answer
166 views

Why can't hot air balloons fly higher then helium balloons?

I have read these questions: Hot air balloon trajectory predictions Do atmospheric physics prevent hot air balloons from ascending over 60,000ft? What is precisely the reason that a helium balloon ...
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How does the temperature of water affect its refractive index?

I am aware this question has been asked many a time but i have never found a answer which satisfied my exact requirements. I recently completed an experiment on how refractive index is affected by ...
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1answer
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Can I eat myself into a black hole?

This was a humorous thought experiment that occurred while chatting about black holes. The person that I was talking to assumed that a black hole required a specific density to be achieved. I pointed ...
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Expression of stress-energy tensor with density function

I try to get the following expression defining the stress-energy tensor in General Relativity ($\big< \big>$ means average) : $$T^{\mu\nu} = \int \dfrac{\text{d}^3p}{E} F(\vec{x},\vec{p})p^{\mu}...
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32 views

Can gas at near-vacuum densities pool at the bottom of containers?

Ordinarily, we assume that a gas expands to fill it's container, however, I've had the thought that at low enough densities, this may not be possible, because the force from pressure would not be ...
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4answers
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Density and Gravity

Let's say we have two spheres. One is twice as dense as the other but they have the same mass. Were you to stand on the surface of each would you experience any difference in gravitational force or ...
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Torricelli's Law and Variable Density

I wish to explore a slight modification of a well known result found in several physics texts - Torricelli's Law of Efflux. The most common problem on the above result has the following setup: The ...
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Density of a perfect fluid

I'm puzzled over an equation used to predict the density of a perfect fluid. I am using this equation for CFD modeling using OpenFOAM. It is used as an equation of state for the liquid in a gas-...
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1answer
28 views

The approximate values of density for a flame with respect to heights

I'm aware that the difference in density with respect to height is low, but I'm in need of the values for a project: in which I explain that the continuity equation of fluid dynamics will work well ...
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2answers
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Pressure under water considering bulk modulus

I want to calculate the under water pressure, taking into account the compression of water. I derived a formula, but apparently the function has a vertical asymptote, meaning that the pressure ...
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1answer
156 views

Density and refractive index of Water/sugar solution

I can't find a correlation or equation for refractive index of water and sugar solution of known density. Do you know where to find it?
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1answer
73 views

Diamond ring around black hole

I know that light takes longer to travel in a denser material, like diamond and I know that black holes also attract light. I was wandering what would happen if you would make a ring out of diamond, ...
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Measuring local properties in a suspension

Considering a fluid with a certain known concentration of particles (eg: 40% per volume RBCs in blood plasma), how do I measure analytically the speed of sound in the medium and its density? i.e. ...
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2answers
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Does the density of water affect the speed of sea waves?

In the case of light waves, the denser the matter, the more slowly they propagate. Do the water waves behave identically?
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1answer
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Neutron star matter density [duplicate]

Edit: Replaced black hole with neutron star, thanks to safesphere for his comment. We're told that tiny volumes of matter have huge mass in a neutron star. For the sake of argument, if you had a 1cm ...
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What atomic forces are acting to resist me pushing an air filled bottle underwater?

Yes air is less dense than water but how does the bottle know to rise or indeed to move? It's not electromagnetism I think. Does this have a relation to gravitational forces? Is it to do with the ...
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1answer
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Can you make a metal denser by melting it and make it cool down under high pressure?

The answer is probably no. But can you make a metal denser by melting it and make it cool down under high pressure? Or would it just crack under internal stress when it returns to a solid? I'm going ...
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2answers
750 views

Hot air balloon - mass

Short background I'm aware that a hot air balloon rises up because of the less density than air. But I'm not sure about how that lower density is reached, and how it can be sustained over time. At ...
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How do I find out the net thrust produced by a propeller?

I am trying to find out the thrust that a propeller produces. Since a propeller can have various different types of inclination for it's blades as well as several parameters such as number of blades, ...
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0answers
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Can I calculate the volume sputtering yield of a compound if I know the atomic component sputtering yields?

I'm running Monte Carlo simulations of a neon beam hitting a $\beta$-gallium oxide target. I set the initial bulk composition to be made of 40% gallium and 60% oxygen (Ga$_2$O$_3$). The simulations ...
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2answers
56 views

Can anyone explain centrifugation? [closed]

Why larger particles tend to remain at the bottom level of the test tube while the smaller particles form a layer above the larger particles?