Flat Definition and 469 Threads

Deviations from the vacuum energy bring about deviations from a Euclidean spatial geometry. Fine; I am not questioning this principle. I am wondering why a Euclidean metric is the base from which everything deviates? An answer that it is the limit of more general metrics only begs the question...

Everything is on the same plane, and I was wondering why. I mean like, if you laid a reallllly flat and thin plate out, then everything rotating around the sun would fall in that, I mean the planets, not comets or whatever.

Homework Statement A uniform flat plate of metal with a circular hole, where it is a rectangle starting from -6 to 7 from the length, and the height is -3 to 3. The circle has a radius of 2, and it starts at 1 to 5. Calculate the x-coordinate of the center of mass xcm of the metal plate...

Homework Statement I have a 30kg crate on a flat floor. There is a rope pulling the crate to the right with a force of 125N. The coefficients of static and kinetic friction are .34 and .24 respectively. I need to know what the minimum force I could put on top of the crate to stop it from...

What is the pattern that maximizes the ratio of surface area of a flat surface to the volume of material used in this surface? The surface has to be flat on a macroscopic scale, but on the microscopic scale could have dimples or other imperfections that increase the SA/Volume ratio. I am...

Alright, everyone, I have some questions in regards friction when rounding a flat curve and was hoping to get some help with it. For that intent, I've borrowed a couple of posts from another old thread on the topic of centripetal force. Hope the authors don't mind. The textbook I'm using...

Special relativity should be a special case of general relativity, for flat spacetime manifolds. For locally flat manifolds, special relativity should however give approximate results. But even Earth is a non-inertial frame. So that would mean that special relativity can only be observed for...

Quick question: from which topological consideration can one derive the fact that a sphere S² does not allow for a globally flat geometry?

If the universe is flat and finite which is where the evidence points today (WMAP) then wouldn't there be an end to space (like an edge). I don't think the universe is curved back onto itself like a sphere because its flat. I mean what would happen if you were to reach the edge of space itself...

big bang contradicts flat universe?? Hi, the data says our universe is flat, but we are also told it starts from big bang into a 3 dimensional world. How can our universe is flat from all direction while we live now in 3 D universe from a big bang? it has to be a curve if it is from big...

Hi there, If you put the Schwarzschild spacetime into a coordinate system in which the time coordinate is identified with the proper time of an observer falling radially from infinity, but keep the other coordinates the same, you get Gullstrand–Painlevé coordinates. Amazingly, it is...

Homework Statement 1. (a) Given that the distances to the sun and the moon are approximately 150 million km and 400,000 km respectively. and that the radius of the moon is 1740 km , estimate the radius of the sun.[Hint:k=9*10^9 Nm^2/C^2, g=10ms^-2) ] (b) Ancient astronomers knew that the...

earth was not flat because ?? ancient astronomers knew that the Earth was not flat because it cast a circular shadow during a lunar eclipse. state another observation that led them to the same conclusion

Its said that a wormhole could allow effective FTl travel by creating short cuts in the fabric of space tme. but if the universe is flat , how would this be a short cut? Doesnt the universe need to be curved for that?

If I understand these terms at all, I don't understand how the Universe can be Euclidean, isotropic and finite in spatial extent, all at the same time. It seems to me that if there's a finite amount of matter in it, then it needs to be closed to be isotropic and it can't be isotropic if it's...

the reason you can't be flat footed in the military is because you have a lot of back, hip, and knee problems. I have wanted to join the military since i was a little kid. but recently i have just found out that i can't since i am flat footed. and that is the reason. I know for a fact because I...

Hi, I apologize if this isn't the right forum for this. I tried to pick that which I felt was most appropriate. My question is about 'flat flex cable'. Somebody I know recently purchased an A/C unit which uses a flat flex cable to connect the control board to the motor and such. They would...

I've been having a bit of a discussion with a friend lately, about an object dropping off a horizontal surface, falling a certain amount, and then landing on another horizontal surface. The question is whether the impact of landing on the horizontal surface, will be affected by the velocity...

Alright last post by me for a while, I'm kind of spamming this forum. I was watching a lecture by some big time astronomer last year (can't recall his name or the link) and he was saying that there are many models for the universe, including flat, hyperbolic paraboloid, spherical, and a few...

Hello, I have a problem I am trying to model analytically (please note: I am NOT a fluid mechanics expert -- I come from a chemistry background): A semi-infinite plate is oriented axially in the direction of flow. Please refer to the following page for an illustration of my problem...

Could somebody explain me what conformally flat is? How to prove a 2D geometry as conformally flat, for example: ds^2 = \phi(dx^2-dy^2) ; phi(x,y) What is class of Einstein Geometry? How to classify Einstein Geometry in 2D?

Does anyone know why every 2D manifold is conformally flat.

Hello, What is the difference between optically flat surface and atomically flat surface?

This is driving me crazy. Consider a two-dimensional spacetime, with coordinates (t,x). If this is a flat spacetime, we can just imagine a regular-old two-dimensional plane. On that plane I could just as easily map a Cartesian/Euclidean coordinate system as a hyperbolic system of coordinates...

When Riemann tensor = 0, spacetime is flat. Is the geometry of this flat spacetime that of special relativity?

I have a fisheye lens which sees 180 degrees of the sky. It registers the entire sky on a 640x480 grid of pixels. Let's assume I know where the zenith and north are on the plate. That allows me to find the alt/az of every pixel in the circular image. The fisheye is linear in the distance from...

Any results from the Planck probe? Has it narrowed down the possibilities ?

Homework Statement A fine hair separates one end of two pieces of flat glass to form and air wedge.when light of wavelength 670 nm is incident normally, 25 dark bands are observed (with one at each end).How thick is the hair? Homework Equations destructive interference: 2nt =...

Homework Statement In a non-accelearting Universe, if the density of the Universe is equal to the critical density, then the Universe is A. open. B. closed. C. flat. D. empty.Homework Equations The Attempt at a Solution I believe the correct answer is flat, but I just wanted to see if...

I'm wondering, now that the universe has expanded and is now pretty much flat, can any experiment we do tell us what might have happened during the Big Bang, when the universe was still small and tightly curved? It doesn't sound like the same situation. The results we get today travel meters or...

I know that the vocabulary for topology/geometry is complex. Please bear with me if I'm not using the appropriate terminology. I'm trying to get a grasp on my question as much as I am trying to find an answer to it. Is it possible for something to disperse throughout a spherical space if the...

Hi! I'm doing physics project and I'm stuck with a really awful paradox.:confused: Universe appear to be flat (nearly), so it should expand forever (the critical universe). On the other hand we've got acceleration of the universe so open model. Which model is the right one?

I was thinking about the equation e = mc^2 and started to get seriously confused. The confusion didn't come from this equation, but from the dimensionality of it, and then the dimensionality of energy itself. So a standard formula for energy for the most part. e = kg (m/s)^2 e...

I am reading Wald's book. There is a problem confused me: page 158, problem 4,(b). An symptotic statoinary flat space, two stationary observer connected with a rope. One observer A is at finite r and the other B is at infinity. Observer B is really stationary by other forces and holding the...

What does it mean in general relativity that space is locally flat. It means that in neighbourhood of each point we can chose such coordinates that the metric is flat or we can do it only in a point (not in neighbourhood - open set).

I recently saw a YouTube video of a 2009 lecture by Lawrence Krauss. He says that we now know unambiguously that the universe (and I just mean the universe that we can see, back to the big bang, not the multiverse or the foam or any of that) is flat. But it seems to me that a flat universe with...

Sorry 'bout posting so many topics but there are too many things that are unclear to me. CMBR measurements suggest the universe is pretty much FLAT, but I don't see it as flat, and forget our planet, all those vast spaces in every spatial dimension - all that is flat? It obviously has depth...

I've been watching http://www.youtube.com/watch?v=Pm5ROyoaMZA" on youtube where it was shown that a cone has curved space (from about 1:05:00). Using the same method of parallel transportation it seems to me that every 3d shape, other than a plane has some points of curvature. However the same...

Why all two dimensional manifolds are conformally flat? Why all manifolds with constant sectional curvature are conformally flat? Does anyone know proofs of above statements. Thanks in advance.

Homework Statement Flat capacitor with a plates distanced d = 2 cm and the area A= 1 dm² are connected to a voltage U = 100 V. We disconnect the source of voltage and we increase the distance between the plates to twice the distance. How much work is done? Homework Equations C= ε*A/ d...

Homework Statement - How much is the electrical voltage U between two evenly electrified parallel flat plates, distanced d = 1 cm, if the strength of electric field between them is E = 1 V / m? - What is the strength of electric field to the left and to the right of each plate? - What is...

I think I read on these forums that a small piece of relatively flat 4D spacetime of General Relativity can be embedded in ten dimensions. What happens if the small piece of spacetime is not very flat, does this change the number of embedding dimensions required? Thanks for any help!

I recently did an experiment to measure the activity of a radioactive source, with the idea that the activity can be found by treating the detector area as part of the surface area of a sphere. In the actual experiment, we plotted u = \frac{n d^2}{\Delta t} against d, where d is the...

I was wondering what equiptment would be best suited to using multiple strian gauges on specific points on a flat steel plate with a central hole in tension. What is the simplest experimental set-up to obtain reading from the gauges? Any points/links would be appreciated.

This is a concept question from a previous final physics exam. The correct answer is (b) and my professor confirms this, but I can't understand why the answer is not (d) since the question seems to imply that the ball is already in rolling motion and that friction would not play a part. A...

Homework Statement I want to be able to calculate how far a ball has traveled when rolled along a flat surface at each second. Lets say the values are 2kg for ball, the force is 100N and co-efficient of friction is 0.2. Homework Equations F(n) = -mg a = f/m The Attempt at a...

Hello all, I have a simple question about copper windings on generators. From what I have read, magnetism only penetrates the skin of a copper wire by very little. Dosnt this mean that most of the copper in a winding is wasted ? And wouldn't it be more efficient to use flat wire "-"...

Homework Statement The problem is Hartle 18.3 and reads: "Consider a flat FRW model whose metric is given by (18.1). Show that, if a particle is shot from the origin at time t*, with a speed v* as measured by a comoving observer (constant x,y,z), then asymptotically it comes to rest with...

Homework Statement In a circular flat track of radius 50m, what is the maximum speed car can go without sliding? Assume the coefficient of static friction between the car tire and the road is 0.4. Homework Equations Unsure of what equations to use. The Attempt at a Solution Unsure...

Hi All, I have a question about the agitator tank. What is the different between dish-bottom, flat-bottom and cone-bottom tank? Regards.