Dust Definition and 172 Threads

Mysteries at the museum, on the Travel Channel started out discussing the history of items at museums. It was interesting and supposedly factual. Last year they added "Mysteries at the Castle" which had interesting stories/myths about old castles. Ok, now they added "Mysteries at the National...

At my Wikipedia-minus-math level of understanding, the problem with any resolution of "Olbers' Paradox" through a fractal distribution (such as the "Cantor set" depicted in the Wikipedia article of that name) of stars or star clusters, rather than the alternative of a beginning of our multiverse...

http://www.wsj.com/articles/radioshack-store-closings-to-jolt-some-developers-1423095564

Hi! It is stated in V. Mukhanov's book "Physical foundations of Cosmology" the following (page 44, after equation 2.25): "In contrast, for the dust dominated universe, where ηmax=2π, the event horizon exists only during the contraction phase when η>π." could someone please explain why is this...

[FONT=Arial]A speck of dust has a mass of 1 x 10-18 kg and carries a charge equal to that of one electron. Near to the Earth's surface it experiences a uniform downward electric field od strength 100NC-1 and a uniform gravitational field of strength 9.8Nkg-1. Draw a diagram which shows the...

(I am of two minds about posting this here or in the main satrophytsics forum, but I think it's probably better to go here.) So, I have a tide-locked planet at approximately 104AU out around a clone of R Coronae Borealis, with has a carefully designed , bright shiny silvery moon (small and...

Planck dust modeling has been released [re: http://arxiv.org/abs/1409.2495] . It appears to be consistent with the assumptions of BICEP2, but, that is an unsupported assumption. I expected an immediate reaction from the BICEP2 team, or other interested parties. Perhaps I am merely impatient, or...

As many are aware, the announced detection of primordial gravity waves by BICEP 2 was heavily criticized based on dust emission modeling. Today, Planck XXV was released which mapped out the dust emissions of Andromeda. Assuming Andromeda is representative of the Milky Way in most relevant ways...

To estimate polarized emission from the galactic dust, BICEP digitized an unpublished 353 GHz map shown by the Planck collaboration at a conference. However, it seems they misinterpreted the Planck results: that map shows the polarization fraction for all foregrounds, not for the galactic dust...

Homework Statement At time t=0 a dust particle of mass m_0 starts to fall from rest through a cloud. Its mass grows exponentially with the distance fallen, so that after falling through a distance x its mass is m_0exp[αx] where α is constant. Show that at time t the velocity of the particle...

Just found out I am allergic to dust mites. This news explains a lot in my health as of the last several years. Does anyone deal with this? I would appreciate any input on how to deal with what would seem like a losing battle concerning bedding. I can deal with getting rid of all the carpet...

I am looking for the e.o.m. of a particle moving inside a sphere of homogeneous dust with density ρ. I start with the Lagrangian (in cartesian coordinates with i=1,2,3) L = \frac{m}{2}\dot{x}_i^2 - \frac{4\pi}{3}Gm\rho x_i^2 The e.o.m. and their solution are given by the harmonic...

Hello all, I need your help. (I believe this si the correct forum) Between 2011 and 2013, i read a news in internet, that the dust that coveres rocks in Mars seem to be very uniform, like all rocks that was drilled by Mars science laboratory twin rovers, seem to have the same thickness of...

Homework Statement A small piece of dust of mass m = 3.8 mu or micro g (micrograms) travels through an electric air cleaner in which the electric field is 526 N/C. The electric force on the dust particle is equal to the weight of the particle. (a) What is the charge on the dust particle...

I have found myself back in the unemployment pool recently. I realized that it was time to dust off my resume and start the job hunt once again. It has been a few years since I have been in the need of employment, but off I go once again. Since I have to get get back in the game and dust off my...

I just heard this on the radio. We had a local try and do this a few years ago. I, for one, am glad someone is watching the crazies.

In various other threads we have been kicking around various equations for a spherical shell and discussing the implications. In this thread I would like to present what (I think) I have worked out about how the shell metric relates to the vacuum metric inside and outside the shell. I hope to...

Consider a perfectly spherical dust shell with a large internal cavity. Imagine there is a moment when the dust is momentarily stationary and there is a string of clocks strung out along a radial axis. At this instant, I will assume that the spacetime inside the cavity is flat and all the clocks...

First I'm hoping this is in the right section. There is a big debate in the high plains of the Rockies and the Pacific Northwest about coal being transported by rail in open top hopper cars. The debate seems to center on coal dust and bits of coal making its way into the water ways. As far as...

Homework Statement A small magnetic sphere of initial mass Mo and initial radius Ro is moving through a space filled with iron dust. During its motion, 5% of displaced dust is deposited uniformly onto the surface of sphere. Given the density of dust to be ρ, find: 1. relation rate of increase...

Hi guys! This is related to a recent thread but since that thread became cluttered, I figured it would be more coherent to just ask the question here. Say we have a congruence of charged dust particles in some space-time with tangent field ##\xi^a##. The energy-momentum of the charged dust is...

Is there an exact solution for the spherical symmetric collaps of pressureless dust? Can one see a Schwarzschild solution for r > Rdust with shrinking Rdust(t) ?

I have been tasked with what seems an almost impossible feat. It sounds simple but for some reason it is not. I am looking for a device that can monitor combustible dust, in this case wood dust from pellets. It must be able to handle concentrations of 50g/m^3. The area to be monitored is a...

Hi all, Here is the problem. I want to try to do some calculations with seeing how much time a relativistic ship has before it can dodge a dust grain. I am having some trouble applying the Lorentz Contraction Equations to get consistent results. Take two frames, the coordinates of the...

Imagine we have a perfect fluid with zero pressure (dust), which generates a solution to Einstein's equations. Show that the metric can be static only if the fluid four-velocity is parallel to the time-like (and hypersurface orthogonal) Killing vector characterizing the static metric. So, I...

I think in a piece by John Baez we learn that the physics of an expanding and collapsing dust filled universe is the same as the physics of a bouncing ball, Radius, R, verses time and height, h, verses time? If so are there counterparts to the kinetic and potential energy of a bouncing ball...

In this 1984 paper on circumstellar dust, the author says, speaking of the emissivity/absorption of dust grains at visual and infrared wavelengths: My question is: where did the expression ##\lambda_p / 2\pi## come from, and what is the physical justification for it? I understand that small...

When a (say 50 meters) asteroid 'A' strikes a larger (say 500 meters) ‘equally hard’ asteroid 'B' at a small angle to the asteroid 'B' would have two vectors, one large vector parallel to the asteroid 'B', another second small vector perpendicular to the asteroid 'B'. ...

Homework Statement How much charge in Coulombs is required to levitate a motionless grain of dust 10 cm above the surface of the moon? Assume the dust grain is a point mass with mg = 1*10^-9g. The gravitational acceleration at the surface of the moon is 1.6m/s^2. Assume charge on the surface...

Question 1: How does the metric relate to the light cone at a particular point? Obviously, the metric should determine the shape of the light cone, but is the converse true? Does the orientation and width of the light cone tell you everything about the metric? I'm guessing not due to the...

What avg density [kg/m^3] may I attribute to solar system space dust? Halliday & Resnick give E-18 to E-21 [kg/^3]. This will allow me to compute solar system density, if I know solar system radius[m], ie, distance from edge of solar system to centre-of-mass of our Sun. By 'space dust' I mean...

Homework Statement Dust particles are 13.0 micrometers in diameter. They are pulverized rock, with ρ=2540 kg/m3 . If you treat dust as an ideal gas, what is the rms speed of a dust particle at 18.0 C? Homework Equations ρ=m/v V=4/3∏r2 vrms=√(3kT/m) The Attempt at a Solution...

I'm not talking about caked on or burnt on brake dust due to years of neglect. I'm talking my car has 5000 miles on it and came out from an oil change with greasy brake dust all over my alloy wheels. I am not the type to scrub my wheels all weekend, so I want to nip this in the bud before it...

I'm currently preparing for a prelim and just wondering if my solution to this problem is correct. I did a plot of v(t) and it looked reasonable. You can find the question and solution both at http://oi50.tinypic.com/2e3v4e8.jpg. The Problem states: A spacecraft of mass m_0 and...

I am a curious (or perhaps bored!) fellow, and as such I noticed something peculiar recently. I was sitting in a car in a garage. The car was stationary and off, and it was facing the east. The sun was beginning to set in the west and a light shone through the back window shield. In the rays of...

Hi can anyone help : Are there different categories of ISM dust ? Where is the dust thought to have come from? Many thanks

NASA's Stardust Mission -- Interplanetary Dust Particles Hello all, I'm currently working on a research paper about IDPs, and I'd like to spend some time discussing NASA's Stardust Mission. I'm wondering if anyone might know of some links to some scholarly articles concerning the matter...

Hi Sorry I'm not good in physics at all. I have the following dust problem becoming attached to Nickel coatings. from what i know Nickel can become magnetic but aluminium should not be attracted to magnets. I did an experiment to confirm if the nickel coat is acting as magnet in...

In GR there is made a clear distinction between a vacuum region and a non-vacuum region as one is handled by the Ricci tensor and the other by the Weyl tensor. But is reality so black and white? And when do we realistically talk about dust and when about fluid? So the inside of an average...

What kind of observation can be made to verify the existence of cosmic dust (space dust)?

http://www.bbc.co.uk/news/science-environment-14680570 Results from the Large Hadron Collider (LHC) have all but killed the simplest version of an enticing theory of sub-atomic physics. Researchers failed to find evidence of so-called "supersymmetric" particles, which many physicists had hoped...

Did this affect any of our members? http://www.weather.com/outlook/videos/time-lapse-amazing-phoenix-dust-storm-21209

I had a funny thought when i was vacuuming. I was vacuuming dust around the multy plug and I decided to vacuum inside. Would electricity go in the tube?

I have a problem with the following scenario: A friend of mine claims that it's possible to start with equations for a compressible fluid or dust and to derive an expanding solution in Newtonian mechanics (!) He claims that this expansion is homogeneous and isotropic (I understand his...

Homework Statement Much of the material making up Saturn's rings is in the form of tiny dust grains having radii on the order of 10^-6 these grains are located in a region containing a dilute ionized gas, and they pick up excess electrons. As an approximation suppose each grain is sphereical...

Homework Statement A particle of dust is bombarded by air molecules and follows a zigzag path at constant speed v. (a)Assuming each step has a length d, find the distance traveled by the dust particle in time t. (b)What is the length of the displacement vector after N steps where N is large...

I have looked through the on-line documentation of the Pioneer Anomaly, and have a simple question: Could the apparent additional acceleration toward the Sun be due to an additional mass of dust which adhered to the spacecraft ? I notice that the authors of the main papers (...

I guess dark matter is the most abundant matter. But which contributes next to the most, intersteller dust or suns?

Homework Statement A uniform, spherical planet of mass M and radius R moves SLOWLY with an essentially uniform speed v through a cloud of interstellar dust particles, whose density is ρ. The dust particles are attracted towards the planet, and some of them would eventually fall onto its...

Homework Statement A typical dust grain has a radius of 10-7 m and a mass of 10-14 g. How many dust particles are there in a molecular cloud containing 1000*Masssun of dusty gas if 1% of the cloud's mass is in the form of dust grains? Homework Equations The Attempt at a Solution...