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Questions tagged [density]

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

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Cosmology - Demonstration for equation of the evolution of the density contrast

In a context of cosmology, I need help about a differential equation that I can't get to demonstrate: The growth of density fluctuations obeys a second order differential equation. At early enough ...
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Do the oil and mercury in this manometer affect the pressure in A and B?

One of my friends came to me with this homework question: We've worked out that the height difference between A and B is 50 mm. That makes the difference in pressure between them $$ \Delta P = \rho ...
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Trouble with two fluid buoyancy problem [closed]

So I've given this problem a few shots and I cannot seem to get a reasonable result. Nor have I found anything really useful online. Here is the problem: A cube with length 10 cm and made of ...
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What Solid/Liquid will become more dense as it gets colder

I am trying to find a chemical that is similar to spermaceti. A substance that becomes more dense in transition from a liquid to a solid, and conversely the opposite when heated to become a liquid. I ...
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Would a rigid object thats slightly negative buoyant sink all the way to the bottom of a 10,000 ft fresh water lake?

Would a rigid object thats slightly negative buoyant sink all the way to the bottom of a 10,000 ft fresh water lake? I'm going to make a few questions regarding the topic involving a submarine & ...
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What would be the distances between compressors part of a gas pipeline from Earth to the Moon?

This paper, acquired from this question about tethers on the Moon, describes LADDER, a mission to deploy a Lunar Space Elevator [LSE]. The space tether, made of Zylon fiber, would be 264,000 km long, ...
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What is the probability of a photon being emitted by the sun actually being absorbed by matter in the visible universe?

In the Hubble ultra-deep field image it is apparent that the visible universe has a lot between us and our light horizon, but what is the likelihood that a photon emitted by our sun actually "hits" ...
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Gradient of pressure - density and temperature dependence

How it related gradient of the pressure to temperature and density of the gas? When temperature is hight and density low why gradient of the gas (or repulsive electromagnetic forses between atoms and ...
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Is it possible for temperature to cause a change in the density of air in a closed isochoric system?

I am taking a meteorology chair as part of a airline transport pilot course and while discussing atmospheric pressure and density the professor claimed that an increase in the temperature of the air ...
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Black hole mass

It has been taught to us that since the black holes have finite mass, their gravitational force is also finite, which totally fits. The Black hole anyhow has a singularity at it's center which is ...
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Why does the speed of sound decrease at high altitudes although the air density decreases?

I understand that the speed of sound is inversely proportional to the density of the medium as shown here and as answered for this question. The problem now is that the speed of sound in air actually ...
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1answer
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What is the density of a static dust sphere in an accelerating universe?

Consider a largish but finite sphere of pressure-less homogeneous dust late in the $\Lambda$CDM cosmology. The outside metric is presumably Schwarzschild-de Sitter with no matter, the interior a ...
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Density of solids and liquids composed of different isotopes

In this question, I am only considering conditions fairly close to STP and moderately but not extremely high accuracy. E.g. a quite well equipped school laboratory. For gases, the density will be ...
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1answer
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From volume density to surface density

Let us say we have a volume $V$ having a volumetric mass(charge) density $\rho(x,y,z)$. Suppose we have a smooth surface $S$ within the volume with a surface mass(charge) density $\sigma(x,y,z)$, if ...
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Is there anything in the universe that cannot be compressed?

I've always thought that there is nothing in the universe that cannot be compressed or deformed under enough force but my friend insists that elementary particles are exempt from this. My thought is ...
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Finding an equivalent shape for a given mass and 3 mass moments of inertia

So I apologize if this is just impossible, but I was wondering if there was a way to find say, the dimensions of a box of a given density that would have the same mass and moments of inertia of ...
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35 views

Does density of an object affects the difficulty in lifting it?

Isn't it that the only thing which affects its lifting difficulty is its mass ? For eg:- There is 1Kg of iron and 1Kg of cotton. Is it difficult to lift iron than the cotton due to higher density of ...
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On moment of inertia calculation of a triangle

I have seen multiple videos on YouTube which start off the process of calculating the moment of inertia of a triangle about it's base by writing it equal to  $\int(y^2\ dA )$ where $y$ is the ...
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Would “buoyancy” / lift power increase if you compressed helium or hydrogen towards 1/infinity?

Of course, my inclination says that density should increase then, having an opposite effect but at the same time, i am inclined to believe that by fitting more helium in a "ballon" would allow more ...
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Does density vary with time in a steady flow?

Steady flow is defined as the type of flow where density, pressure and velocity don't change with time, as far as my understanding goes. However, in the video below, they say that the density in a ...
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1answer
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What is the significance of kinematic viscosity? [duplicate]

We know that kinematic viscosity is defined as ration of dynamic viscosity to the mass density of a fluid. $\nu = \frac \mu \rho$ But I want to know the significance of that physical quantity of ...
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How does climate change affect air density? [closed]

At first I thought... if the overall temperature of a planet goes up, then the gaseous atmosphere will be hotter, so it will have lower density than it used to. So overall density should go down. ...
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1answer
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Find the density of air at the given temperature and pressure [closed]

Find the density of air at $99$ kPa and $322.15$ K. My attempt: Let's assume that air is $78\%$ nitrogen and $22\%$ oxygen by volume. Average molar mass of air = $0.78\times 28+0.22\times 32\approx ...
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Do elementary particles have a density?

The SM supposes elementary particles are structureless unless composite objects like hadrons. For bosons, that can occupy the same state, we can define energy or mass density. The same happens but ...
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1answer
62 views

Correlation between the refractive index and the density

The $v$ propagation speed of light in a transparent medium is related to the $c$ speed of light in vacuum through the relationship, $$\boxed{n=c/v}$$ The constant $n$ is a pure number called ...
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Liquid nitrogen physical properties

I am looking for a reference containing the physical properties of liquid nitrogen, in particular density $\rho$ and dynamic viscosity $\mu$ as functions of temperature and pressure. This is for a ...
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1answer
167 views

Formula for the bias of galaxies

From the article "Large-Scale Galaxy Bias", I try to deduce the equation that my teacher told me which links 2 quantities: the global number density of galaxies the local number density of galaxies ...
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Density of water after absorption

I was wondering if I could assume a water density ~1.0 g/cm3 after it was absorbed by the skin, or other medium. I am particularly thinking on a molecular level, if the nanostructure and size of ...
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Demonstration about large-scale bias of galaxies

From this article : https://arxiv.org/pdf/1611.09787.pdf , I try to deduce the equation that my teacher told me which links 3 quantities : 1) the global number density of galaxies 2) the local ...
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What is buoyancy?

I’ve seen answers which cite newton’s third law as the cause for buoyant force, but wouldn’t this mean the moment an object of any weight is placed on a fluid, the fluid would immediately exert an ...
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Hubble Parameter in terms of Density Parameters

So I have the equation (derived from the Friedman equations with $a(t_0)=1$ and the powers of $a(t)$ quoted)$$H^2 = H_0^2\left(\frac{\Omega_{R_0}}{a^4(t)}+\frac{\Omega_{M_0}}{a^3(t)}+\Omega_{\Lambda_0}...
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81 views

Can density replace buoyancy?

Recently I discussed the possibility of a flat earth, with a flat earther whom rejected much of established science, especially newton and his laws because Newton's idea of gravity rendered a flat ...
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Is there a limit to the amount of mass we can concentrate in a region of space?

Black holes are solutions to Einstein's Field Equations. Black holes contain a singularity hidden from the outer universe. As I understand, these singularities are infinitesimal and contain a very ...
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What are typical atomic densities of solids and gases? [closed]

What are average values for the number of atoms per cubic cm for typical solids and gasses at atmospheric pressure?
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volumetric density from linear densities in the three directions x,y,z

I have a cube and I know the linear density of particles along each axis (I mean- the number of particles per unit length along each axis). How can I get the volumetric density?
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How is water heavier than petrol, even though its molecular weight is less than petrol?

Molecular weight of petrol is so much higher than water, but when it comes to physical property, weight, one litre of water weighs more than one litre of petrol. How is it possible?
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Why does a helium balloon rise? [duplicate]

This may be silly question, but why does a helium ballon rise? I know it rises because helium is less dense than air. But what about the material of the ballon. It is made up of rubber/latex which is ...
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4answers
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Does a non-buoyant (denser than water) object (such as a lead diving weight) weigh any less when submerged in water?

I've just been discussing this question with my eldest son, who is an extremely intelligent man, as well as being an engineer, a sailor and a scuba-diver, and he believes that an object heavier than ...
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1answer
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Does optical density depend upon concentration of a solution?

Does optical density vary upon the amount of salts dissolved in water?
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1answer
58 views

Does the density of an object play a role for it's gravitational effects?

My thought experiment: We repalce our sun with an object of identical mass, rotation, shape, etc. but not the same density, i.e. the object would have a radius of 100km. The "replacement-time" would ...
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1answer
73 views

What does Earth feel like when squeezed?

he average density is about 4g/cm^3 so if the earth was in the size of an orange, it would feel like a rather heavy ball. The crust is relatively thin, and the earth is said to be solid land masses ...
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Negative probability distribution function for Dirac equation

People say that the probability density function of the continuity equation for the Dirac equation is definite positive. I wanted to see it myself and followed the same path as Bjorken & Drell's ...
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How do we know that dark matter energy density scales as $\rho\propto a^{-3}$?

How do we know that dark matter energy density scales as $\rho\propto a^{-3}$?
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Is the universe be expanding at different rates depending on its temperature and density?

As I understand it, when observing different regions of the universe we get a different rate of expansion (the two Hubble constants), specifically the more distant observation seems to return a lower ...
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1answer
114 views

Black hole gravity and light [duplicate]

When an object is squeezed to its Schwarzschild radius it becomes a black hole (made by density) and its mass does not change (its gravity doesn’t change), but if its mass doesn’t change (its gravity ...
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Phase diagram of a fluid

How is it look like the phase diagram of a fluid in density-pressure plane? I came across the phase diagram in Pressure-temperature plane most of the time. But I can't find the phase diagram in ...
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36 views

Prove electric field is continuous at an external point $P$

I have a continuous charge distribution with density $\rho$. Can anyone please tell how shall I prove the electric field is continuous at an external point $P$? $\displaystyle \mathbf{E}=\dfrac{1}{...
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Is it possible to have mass with zero volume?

As we had always studied that matter occupied space and has mass and our universe is made of matter so do that mean that there is no case where mass is present without volume .
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Why does sound not move through a wall? [duplicate]

I'm learning a bit about sound and was wondering: If the speed of sound is determined by the amount of matter the source is surrounded with, why doesn't it go through a wall? Example: Speed of ...
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Cosmological densities when universe was/will be a different size

Supposing a spatially flat, matter-dominated universe, the expression for the Hubble parameter is: $$ H^{2}=H_{0}^{2}\left(\frac{\Omega_{m}}{a^{3}}+\Omega_{\Lambda}\right) $$ The previous equation ...