What is Flat: Definition and 495 Discussions

So CMBR points to a flat universe, and this seems to be the generally accepted model. But in a flat universe is expansion not supposed to slow exponentially, stopping after an infinite time? How does this fit with the observation that distant type Ia supernovae show the universe's expansion to...

hahaha Dave

I want to rotate an inclined plane to achieve a flat surface. I think I can use the Euler angles to perform this operation. Using following data: and following rotation matrix I think you can make the plane flat by following rotations: 1: rotation around x-axis by 45° 2: rotation around...

Homework Statement 1) Calculate the angular diameter distance to the last scattering surface in the following cosmological models: i) Open universe, ΩΛ= 0.65, Ωm = 0.30 ii) Closed universe, ΩΛ = 0.75, Ωm = 0.30 ii) Flat universe, ΩΛ = 0.75, Ωm = 0.25 Describe how the CMB power spectrum...

Hi all, I have a bunch of legacy files I am trying to import directly into an .sql database. Is there a way of doing this other than by using Microsoft's import/export Wizard?

I'm reading A. Zee's GR book and I'm in the section in which he is showing how to transform coordinates to be locally flat in a neighborhood of a point. He said that we can always choose our neighborhood to be locally flat for any space of any dimension D. "Look at how the metric transforms...

Physicists have observed the cosmic radiation background to conclude that the universe is flat (or within the margin of error of being flat). This means that the Universe contains the critical density needed to keep it flat, which is a mix of ordinary matter, dark matter and dark energy (I...

Homework Statement Find the locally flat coordinates on the Poincaré half plane. Problem I.6.4 by A. Zee Homework Equations [/B] Poincaré Metric: ##ds^2 = \frac{dx^2 + dy^2}{y^2}## The Attempt at a Solution First, I'm having problems with the explanation in Zee's book. He said that we can...

Not a joke successful rapper refutes ball earth; https://m.soundcloud.com/bobatl/bob-flatline-feat-neil-tysonThe push back from Neil DT nephew;

I'm reading the book by Zee, I came across a paragraph saying that the world is not flat. "Given an airline table of distances, you can deduce that the world is curved without ever going outside. If I tell you the three distances between Paris, Berlin, and Barcelona, you can draw a triangle on...

Rapper B.o.B. says the Earth is flat; NdGT responds by dropping a diss track*. Flat To Fact (feat. Neil deGrasse Tyson) (B.o.B Diss Track) *well, his nephew anyway.

A well known math theorem says that - if the spatial dimension is odd - D'Alembert equation gives rise to a solution containing a term which is completely supported on the light cone. A mathematical wrap up could be the following: "in dimension 3 (and in fact, for all odd dimensions), the...

Hi All! See the picture. A-Consider a flat plate physically moving perpendicularly through the air. B-Consider this same flat plate sitting perpendicularly and stationary now in a wind tunnel where air is made to flow. Accordingly if airspeeds, areas etc are similar, the 2 situations...

A lot of cranks on the net make a lot of the torus - of course magnetic fields are toroidal - but not space time right? Or could it be - a torus is flat (zero gaussian curvature) which is how we observe the universe to be as far as we have measured it's curvature on large scales - and it would...

I understand the bit about liquid crystals and polarization of light. The question is how the screen is made. Is it full of a a matrix of tiny wires? How is it made so precisely?

I've been struggling with part (a) of this question. I'm not quite sure what the relation is. Any help is greatly appreciated! Thanks! Consider a spiral galaxy with a “flat” rotation curve beyond the central 2 kpc. a. Derive the general relation giving the orbital period, P, of a star (or...

OK, sounds nutty in a limited short title, but... For a planned dome home in an area where average annual air temperature is 72 degrees, and thus steady state ground temperature at 20' deep or so stays within a pretty narrow range near that 72 degrees year round average above, and where house...

Homework Statement A puck is sliding on flat ground with initial speed to 4 m/s and comes to rest after 2 s. Aprox. which is the coefficent of kinetic friction between puck and ground. 0.9 0.6 0.5 0.4 0.2 I don't know how to solve for this. I ended up in this class accidently and never took...

The Nusselt number for an entire flat plate in the turbulent region has two different equations: One for Turbulent and one for Combined Laminar and Turbulent. How do I know when to use one or the other?

Hi, I have a question regarding calculating Young's modulus for a flat spring. I have a flat spring shown as the left one in the image. Now I fix the bottom of the spring and exert a force F on top of it and it bends for distance of d. Is there any way to calculate young's modulus for this...

Is this a break though or just hot air? http://arxiv.org/pdf/1510.05534.pdf We do not claim that the Mestel (1963) disk is the answer to establishing the universality of flat rotation curves in galaxy disks; only that it has always been a telling clue that gravity does not pull the strings and...

A stunt car is driven along a flat train car. The stunt car is moving toward the engine of the train. How would you calculate the velocity of the stunt car relative to earth? Im in physics 11 and we are almost done our velocity chapter and this question was on our review.

I am trying to solve a homework problem that involves Work and friction but don't understand why if a force pulling upward on the object, the normal force becomes N = mg - Fsin(o) shouldn't it be N = mg + Fsin(o) since both forces are acting upwards? (the normal force and the force applied)

I'm new to this impressive forum and have a question that may have been addressed a thousand times, but here goes. A FLRW metric is happy with a time-varying scale factor a(t) and zero curvature parameter k and could care less about density. The combination of a FLRW metric and the Einstein...

Hello everybody I just got an old underbone bike, which I'm planning to build and finish before the end of this year. I found the engine to be quite pathetic (a 4 stroke, carburetted, 100 cc flat engine) so I'm going to do an engine swap with a more powerful but similar engine configuration...

As an amateur, I am just testing my understanding on the following, since there is nothing worse than harbouring misconceptions. Suppose we have a space-time ( e.g. of FRW type ) which is conformally flat : C{^{\mu \nu }}_{\rho \sigma }=0 but not Ricci flat : R_{\mu \nu }\neq 0 Would that...

A heavy board is fixed to another flat surface along its entire upper edge and not moving. How can I find the tension force that is acting on the board? Is it the same as if the board would be fixed to a string in the middle of the upper edge and hung and then the tension would be T=mg?

if in a solid there arent no states with same energy then why energy band vs location diagram is flat?

Hi guys, I am new to the forum and I have what is probably a simple question for most of you. Unfortunately a great deal of people I know have suddenly taken up the idea of a "Flat Earth", and they consistently post things that try to contest that a flat Earth is a far more logical idea than a...

I'm trying to get comfortable with the idea of a flat torus topology that is also an everywhere a smooth manifold like the video game screen where you got off the screen to the right and pop out on the left (because as I understand it this topology could be a model of space) I can't get how...

What is the difference between General metric gαβ and flat metric ηβα in GR? Elaborate answers are appreciated.

I've been working through Leonard Susskind's "The Theoretical Minimum" lecture series (which are a fantastic introduction to the topics covered by the way) and a couple of his comments confused me when he was covering the Kruskal-Szekeres metric/coordinates in General Relativity. The end of the...

whatis the difference between flat and thin plates?

The concept of the fabric of time and space is confusing to me. I understand that an object with large mass can warp it, but that only makes sense to me if the fabric had only two spatial dimensions (assuming no warps). The space-time fabric is always explained visually as a flat plane, but...

Suppose there was a universe that was small, and flat, but globally it was connected like a torus. Basically, pac-man's universe (except special relativity is in effect). The space ##(\mathbb{R} \pmod{1})^3##. Does this assumed universe have a distinguished inertial frame where the...

My understanding: When we draw a triangle on a flat piece of paper and measure the angles using a protractor, the sum of the angles is ##180^\circ##. So we conclude that the universe is locally flat. Suppose we draw a very big triangle that spans across galaxies (say, using lasers and mirrors)...

I've been reading about how much of a sphere actually touches a flat plane (spheres are very interesting things, it turns out!). Mathematically, a perfect sphere has only one point of contact, meaning that the area of this contact is infinitely small(?), but as physicists, we know that there...

Hi, my question is the title, if Ricci tensor equals zero implies flat space? Thanks for your help

Homework Statement A wheel rolling on a horizontal flat surface at a constant velocity experiences no friction force. Why? A wheel rolling on an inclined surface at a constant velocity experiences friction force. Homework EquationsThe Attempt at a Solution A wheel rolling on a horizontal flat...

I need someone with more experience in the field who has knowledge of excel to check over my work. Given the gravitational attraction between two bodies is F = (GMm)/r^2, and the centripetal force required to keep a body in orbit is F = (mv^2)/r, therefore (mv^2)/r = (GMm)/r^2 therefore...

I am a Post graduation student and I am doing a project on the conversion of a Gaussian beam into a flat top beam using optical components. I have found that the best component to do the same is a Powell lens. I would like to know more about the equations connecting the input beam diameter...

Homework Statement Coefficient of friction of a flat belt and of a vee belt Homework Equations I know the lap angle, m2, T2, T1/T2 and ln (T1/T2) for the flat belt and lap angle, m2, T2, T1/T2 and ln (T1/T2) The Attempt at a Solution I attempted to find it by plotting a graph using the lap...

we are building a hydrotesting chamber, the steel plate will be a sheild wall. if something goes wrong in pressure testing the steel plate should withstand the pressure without deforming, i am stuck in how to calculate the thickness applicable to withstand it. hydrotesting pressure is 25,000 psi...

Homework Statement Homework EquationsThe Attempt at a Solution I could know the pressure in point B If I calculate the heigh of pressure I got: But I don't know where is my free surface in the container 3, is it down?? I don't know how to keep doing it...

I am designing a flat plate heat exchanger for a project and I am not sure where to start with the hand calculations, specifically the LMTD and E-NTU methods, also how to work out the parameters which i will need to complete these methods such as area and number of plates. My deadline is soon...

Hello! I've read somewhere that the universe is flat and this can be proven by the fact that CMB is homogenous. I still don't get the idea. So, can anyone explain it to me in more detail? Please do correct me if I'm wrong. Thank you.

A problem of photogrammetry How can be demonstrated that the terrain in front of the plane you see in the photo is flat and there is no slope going down there? First flight, 120 feet in 12 seconds, 10:35 a.m, December 17, 1903; Kitty Hawk, North Carolina. Orville Wright at the controls. If...

My understanding is that the degree of flatness observed for the spatial universe is quite extraordinary, to the extent of begging for an explanation. If this is correct, then my question is, what are the (most) plausible mechanisms being considered as an explanation for either an exact, or...

Hi I am new to this site, I'm currently studying my Engineering Foundation degree and I am massively struggling on the theory side to pulley tensions. Please could anybody point me to some sites or some information which would help me understand and answer this question in detail. I have not...

Good day, everyone, I have an uncommon question: Man smokes in a balcony. Will the people, who are below him will smell that? Or just people who live above the man? I guess warm air is going up, but how about a smell, diffusion says that molecules are moving disorderly, so I completely lost my...