# Topics about density - 142 Discussions, Page 1

1. ### B Could Archimedes' problem have been solved a little differently?

When I was reading this page to understand Archimedes' 'story' I got a question: http://hyperphysics.phy-astr.gsu.edu/hbase/pbuoy.html#buoy According to the example shown, Archimedes found the density of crown by finding the apparent weight. What if he had just measured the volume of water...
2. ### I Computing the Density of a Point Cloud

Hi. For some background, I am running molecular dynamics simulations of silica fracture in LAMMPS. Each point represents the location of a broken bond. I would like to find regions where many bonds are breaking, which I speculate would be locations of crack formation. These computations are...
3. ### An exercise with Pascal's Law

Answer : Using Pascal's law, this is my answer : ##\color{blue}{\boxed{\vec F_a = \vec F_c < \vec F_b}}##. Reasoning : Forces ##F_a## and ##F_c## are equal because the pressures required at the two cylinders for case (c) is the same as that required in (a). It doesn't matter how many of those...
4. ### I How do I read this equation for air friction/drag on an object?

I am trying to understand an excerpt from an article describing the vibrations of a string (eg. guitar/piano) which reads as follows: This is basically the wave equation with Δm representing a small piece of mass from an interval of the string and two forces added to the right side. He...
5. ### Origin of potentials

I think the right choice is c. I'll pass on my reasoning to you: We can think that if the formula of the potential is V(r)=\dfrac{kq}{r} If r tends to infinity, then V(r)=0. But the correct answer is d).
6. ### Pressures in a U Tube along a line - different liquids

Yes, pressure is same along the line for both the tubes since the liquids are in equlibrium. (I ignore the slightly longer air column in the left compared to the right). Is my answer correct?
7. ### Gauge pressure due to a floating body

My answer : Both pressures are equal, i.e. ##\boxed{P_A = P_B}##. Reason : (1) The block of wood displaces an amount (mass) of liquid equal to its weight (archimedes' principle for floating bodies, or law of floatation). Hence we can imagine removing the block in the second case and filling it...
8. ### I Maths for Sound passing through different mediums

What is the mathematics involved with calculating the energy lost from sound as it passes through different mediums? If I started off with a 70dB(A) sound wave, and after 0.5m it passed through 10mm of mild steel - what would be the sound level (in dB) 1m away from the steel plate? To clarify...
9. ### Weight of water with objects floating

We understand that the crucial thing about the problem is that the volume of water present in the three containers are not the same. Also, we note that in each case the weight of the container is the total weight of its contents. (A student might be confused as to why should be so - after all...
10. ### A Superionic and metallic states of water and the Anomaly of Water

https://www.wired.com/story/a-bizarre-form-of-water-may-exist-all-over-the-universe/ Black ice I knew the Black Ice Theories since around 1990 https://www.nature.com/articles/s41586-019-1114-6 -- Demontis, P., LeSar, R. & Klein, M. L. New high-pressure phases of ice. Phys. Rev. Lett. 60...
11. ### Engineering Composite Material Density

Does anyone have an equation for the resultant density of the composite materials? Having a look around the internet and I can't find anything, there was this one website that gave me a step-by-step but the answers did not match (sciencing.com)
12. ### A Equilibrium point of matter and radiation density

We want to calculate the ao/a(teq) of the equilibrium point between ρm and ρr (ρm= ρr ) My book solves it this way; ρm(t) / ρr(t)= a(t) ⇒ ⇒ (ρm/ ρr)teq =1 = = (ρm/ ρr)o * a(teq)/ ao I don't understand the a(teq)/ ao part. If ρm(t)= ρο/αo3 and ρr(t)= ρο/αo4 then it should be ρm(t)/ ρr(t) =...
13. ### I Would an unstable emulsion separate in the abscense of gravity? How?

If you have two different liquids (water and oil for example) mixed together and free floating without gravity, will they separate as they do here on Earth? If so, what property would determine the layering structure? I suspect they would separate, and if left undisturbed probably form a...
14. ### B How to find inverse steradian from arcmin^-2 for density of galaxy

Hello, I am using a code on EUCLID future mission. The original author of this code has set a value for the density of galaxy equal to : ng = 354543085.80106884 I think this is expressed in inverse steradian. I think that EUCLID mission has a 30 arcmin^-2 value for density of galaxies...
15. ### A Different FRW Cosmological Models

ρο/a4 ρο/a3 k Λ Βig Bang Big Crunch Polynomial Expansion Exponential Expansion x 0 x 0 >0 x +1 x +1 x 0 <0 x -1 x -1 >0...
16. ### B Would there be an upper limit to density in QM?

Admitted I know very little about QM, but I've been thinking about black holes and I wondered if there would be an upper limit to density of an object of the smallest size allowable if the particles are not being observed by anyone (since black holes are black)? I ignorantly wondered that...
17. ### Determining the flow rate for a cooling system

MODERATOR'S NOTE: HOMEWORK INCORRECTLY POSTED TO CLASSICAL FORUM, SO NO TEMPLATE I need help with the following question: Please have a look at the question and my attempt at the solution. Alternative cooling systems are considered for a large computing centre requiring 1 MW of cooling...
18. D

### AlGaN density

Hi, does anyone know density of Al0.1GaN. I have searched throught the internet but could not find anything. If possible send me some list of material properties to have some credible source of information for my work. Thanks.
19. ### B How can I model a density function of a compressible fluid?

I have a cylinder of some dimensions. I have a compressible liquid inside. Assuming a constant temperature, no atmosphere, no convection currents within, because it is in a cylinder, there will be no variations in density horizontally (the fluid will have time to settle). Now because there is...
20. ### Calculate the density at the centre of the Sun

Homework Statement Assuming you know the core mass, and other data about the sun, such as temperatures and pressures. Find the density at the very center of a star. Homework Equations I think this may be involved. P(r) = p(r)/µmH kT(r) The Attempt at a Solution [/B] I don't know where to...
21. ### I Infer the distance of a closest neighbor galaxy from correlation

I am trying to estimate the distance of closest galaxy neighbor knowing the expression of number of neighbors into a volume ##\text{d}V##, the mean density ##n_\text{gal}## and the correlation function, i.e with this expression : ##\text{d}N=n_{\text{gal}}\,\text{d}V\,(1+\xi(r))## with...
22. ### I Total number density of galaxies and problematic expression

Hello, I am asked to give the formal expression of the total number density of galaxies and explain why is this expression problematic in practice? From what I saw from my research and into my lectures, I have found the follwing relation which gives the number of galaxies ##N## with mass ##(m...
23. ### Is this kind of pressure chamber design possible?

Hi! Given that the chamber is airtight and no air leakage occurs, is the design in the picture below possible? Can the pressure inside the chamber cause the button (black part at the top) to be "pushed"? https://imgur.com/a/wOSD30D Obviously the temperatures are over-exaggerated, but the...
24. ### Density-density correlation function for spinless Fermions

Homework Statement Consider the groundstate of a one-dimensional, non-interacting system of spinless fermions. Let ##a^†(x)## and ##a(x)## be the creation and annihilation operators for a fermion at the point ##x##, so that the density operator is ##n(x) = a^†(x)a(x)##. Show that the...
25. ### I Gas density and plasma

In general, when we say that in a fermionic gas the higher its density, the better we can consider it to be a plasma instead of gas?
26. ### I Distribution of nucleons in the nuclei

What does this diagram tell us about the distribution of nucleons in the nuclei? - The diagram is from Krane Introductory Nuclear Physics I know that nucleons don't congregate around a central part of a nucleus, but instead have a constant distribution throughout. i.e. The number of nucleons...
27. ### B Density of the early Universe contributing to the red-shift?

Does the relative density of the early universe contribute to the red-shift of distant galaxies? If so, by how much? How would this be calculated? Asked another way : Assuming both the early universe and the current universe are flat, could the relative difference of their space time metric...
28. ### How do I find the terminal speed of a body in water?

Homework Statement A baseball has a terminal speed of 42 m/s in air (ρ = 1.2 kg/m^3). What would be its terminal speed in water (ρ = 1.0 x 10^3 kg/m^3)? A) 0.05 m/s B) 1.5 m/s C) 18 m/s D) 42 m/s E) 1200 m/s Homework Equations D=½Cρ*Av^2 where the magnitude of the drag force (D), relative...
29. ### Effects of Temperature on Flow Rate

Using a pump we are cycling water through a capsule with filter media inside; while measuring the flow rate (l/min) and the pressure (psi) going in and the pressure going out. The water is cycled back into the same storage tank. As the flow rate increases the differential pressure should change...
30. ### I How to control the weight of an object?

Hello everyone, First off, i would like to apologize for any spelling errors. I am Portuguese and my english is going to be very simple. I am in the process of building something and i am reaching out to the physics community for help solving a problem. I am a CNC programmer and while i was in...