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

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What happens when I increase the density of a stellar object so that its mass surpasses the Schwarzschild limit?

We know that every object that has mass, also has a Schwarzschild radius $r_s$: $$r_s = \frac{2Gm}{c^2}$$ With $G$ being Newton's gravitational constant, $m$ the mass of the object and $c$ the speed ...
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2k views

How much lift does the average latex helium filled party balloon produce?

How much lift does the average helium filled party balloon produce? (not including any extras like ribbon string)
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157 views

Gaussian integration and dimension argument

I made a mistake recently regarding the Gaussian density, by putting the determinant of the variance to the power $\frac{d}{2}$. Would the following argumentation be valid to highlight it should be to ...
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107 views

How wide does a wall of ice need to be to stay in place?

Let us say that we have unlimited manpower to construct a huge wall of water ice e.g. 200 m tall (700 feet). -and that the wall is placed in a climate, where the temperature never (for your purpose) ...
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131 views

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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398 views

Does the Relative density of water change based on the state it is in

Will Relative density of water change based on the state it is in? Ie solid, liquid, gas. What causes this change(if any) in Rd?
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1answer
127 views

How to calculate upward force of a container filled with a less dense gas than the surroundings where it is placed?

I'm trying to determine the calculation which would state the upward force of a container where the density inside the container is less then that in which it sits. Does this calculation change with ...
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1answer
81 views

Singularity in a black hole [duplicate]

This might be a naive question, but how can an object such as a black hole singularity have infinite density but finite mass? (For example, we can approximate the mass of a black hole based on ...
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1answer
290 views

Does increasing the density of a solution decrease the rate of temperature change?

I did an experiment to compare whether salt water (5% concentration of salt) or fresh water of the same volume took longer to heat up to a certain temperature. We found that salt water took longer to ...
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3answers
774 views

charge density in a wire

If we have a infinitely thin and infinitely long straight wire on the $z$-Axis with given current $I(t)$, how can I compute the charge density? I figured out that the current-density is given by ...
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209 views

What is electron density and its unit in plasma physics?

I can not find (through Google search engine) that what means electron density and what is its unit? and what is there relation between electron density and electrical conductivity?
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197 views

Calculating Air Density Lapse With Altitude (Specifically, pressures)

This might be a bit more of an engineering question, but I'm calculating air density drop-off with altitude, and I'm having some problems calculating the pressure (I'll run through my method). This ...
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1answer
98 views

Measure density with the help of buoyancy

I am trying to derive a formula to calculate the density of a irregulary shaped object. I can measure the (false) weight of the object in pure air (of known density), and the (false) weight of the ...
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If hydrogen and helium are lighter than air, why won't liquid hydrogen and liquid helium defy gravity?

Title says it all. If hydrogen and helium are lighter than air, why won't liquid hydrogen and liquid helium defy gravity?
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936 views

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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2answers
85 views

Point masses and infinite densities

Point masses are masses who don't have volume. It is said that they are infinitly dense, but I though division by zero is undefined hence you can't define the density for a point mass because ...
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128 views

What causes liquids to have different densities?

We know that different liquids have different densities and it is mass over volume. When the mass is more, then its gravitational attraction will be higher (Compared to other lighter atomic mass ...
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1answer
81 views

is gravitational force dependent on objects radius?

I was told that objects with the same mass but different sizes (or densities) will have a different gravitational pull. Is this true? If so, why?
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3answers
184 views

Center Of Mass Troubles

I understand the concept of Center Of Mass(com), but I am having a difficult time interpreting the equation of the simplified case of one-dimension. The book I am reading defines the position of the ...
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2answers
383 views

How to correctly solve density tolerance

I want to know if my solution to a textbook problem has any major problems with it. Here is the problem: Ethanol has a given density of 0.789 g/mL at 20 degrees Celsius and isopropanol has a given ...
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40 views

Density as a function of Temperature?

I know that volume = mass/density....and density is the function of temperature. Is there any standard equation that describes density as a function of temperature? The system I am interested in is ...
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2answers
82 views

Density of a material in different dimensions

Hope this isn't something trivially wrong, I am a beginner in classical mechanics. But anyways, say there is a cube, of side length $a \ \text{cm}$. The volume of the cube is $a^3 \ \text{cm}^3$. If ...
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272 views

Density of Air in a balloon

A balloon with volume 2800 m³ is heated up to 60 °C. If the outer temperature is 12 °C and the air has a pressure of 960 hPa, what is the density of the air inside the balloon and on the ...
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3answers
254 views

Temperature and density

As temperature rise the density become lower,When temperature goes down, density is higher but in higher temperature the body become bigger so why density become lower?
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30 views

Finding a 1-Dimensional Mass Distribution

Past Discussion There have been a lot of questions and discussions regarding determining the mass distribution of various bodies through non-destructive purposes. Here are a few: Determination of ...
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29 views

Proton gas density

As far as I know the lightest gas is hydrogen due to low mass of its nucleus, but what if we were to somehow strip hydrogen atoms of electrons and enclose protons in a container made of teflon (high ...
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36 views

Hydrostatics , work Power and Energy [closed]

If a servant lifts 10 cubic meter of liquid from a tank, which is at a depth of 40m . If the work done by him is 1600J, then find the density of the liquid (g = 10 m/s^2)
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54 views

Compressed air in a volume: Can I determine its temperature?

Using a compressor, I augment the pressure in a volume (using atmospheric air). I only measure the pressure inside. I now that the density will increase however, the temperature decreases. Can any one ...
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1answer
63 views

What does the absence of hydrodynamic entrance effects do to the momentum conservation Equation?

I am trying to do a homework problem where we re-write the mass, momentum and energy conservation formulas for downward flow in a vertical pipe and it says "where all hydrodynamic entrance effects ...
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3answers
183 views

Possible Rock Density Determination Method

I am trying to do density determinations on a large number of individual rock samples. I know the standard dry weight - wet weight methods but have an idea that might be better. I can buy a ...
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98 views

Energy transfer by a rotating disk at a constant RPM

Does Energy transfer from a rotating disk at a constant RPM into ambient fluid depend on disk material density? Why?
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506 views

Linear charge density, surface charge density and volume charge density

What is the difference among: linear charge density, surface charge density, and volume charge density?
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42 views

Does gravity cause Archimedes' principle and how?

Why do lighter objects float and denser sink? I understand this from the perspective that if the object can displace the equal mass of water it will float, but I wonder from the perspective of ...
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49 views

Effect of waters changing specific gravity on objects apparent weight placed in liquid

My goal is to monitor the change in specific gravity of a liquid over a period of time. My question is: What are the appropriate formula for determining expected apparent weight of an object immersed ...
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27 views

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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94 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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298 views

Archimedes' principle for two liquid layers

Problem: I have a cylindrical vessel of height $H$ and radius $R$. There are two liquid layers in the vessel. The first has density $D_1$ and height $h_1$, the second has density $D_2$ and height ...
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63 views

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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29 views

Electromagnetic Energy and Momentum

I'm trying to show that the electromagnetic energy density and momentum density satisfy the inequality: $ u \geq c |\vec{\wp}| $, where $\wp$ is the momentum density and $u$ is the energy density. I ...
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76 views

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 ...
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54 views

Stress and Mass Density Distribution

I'm simulating electromigration in a copper wire using COMSOL and trying to see the back-stress caused by material transport. However, I do not see any stress growth. In other words, the atomic ...
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1answer
187 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. Also does the conductor length need to be considered finite and equal to the core length or will the calculation be for infinite ...
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257 views

Mass, Volume, Density, and Pressure of Balloon Inside a Balloon

I'm not a physics guy so I'll apologize from the start if I put some erroneous terms. I just want to know the relationship of mass, volume, density and pressure of the two balloons if balloon A is ...
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2answers
149 views

In a glass of water, will an ice cube ever touch the bottom?

No matter the mass of the ice cube or the level of the water, will the ice cube ever touch the bottom of the glass or will there always be a layer of water in between?
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1answer
35 views

Boundary conditions for the heat equation when solving a mass density gradient

I'm working with a mass density gradient with length $L$ and I'm trying to solve the heat equation in 1-D (mass diffusion equation, $\partial_t\rho(t,x)=D\Delta\rho(t,x)$), but I'm not sure which ...
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179 views

Suppose a hollow metal sphere filled with helium is dropped in a body of water

What are the conditions that would cause said sphere to sink or float? What if the sphere was full of ice instead?
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2answers
66 views

Fluids and density [closed]

Is the answer C? Assume that you look at three objects that all float on water, but have different shapes and sizes. Which one has the greatest density? A.The object that has the largest fraction of ...
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1answer
344 views

Percentage of water that is void or empty space?

At the atomic level, at sea level on earth, what percentage of normal pure drinking water is void or empty space? What percentage of lead (the kind used to insulate from nuclear radiation) is void or ...
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2answers
72 views

Thermodynamics of thermometer

Mercury is used in thermometers because it increases in length significantly due to rise in temperature, However, mercury has high density relative to water, which means more inter-molecular forces ...