What is Flat: Definition and 495 Discussions

How is the force to move an object on a flat service calculated? Does it mater if it's flat or on edge?

Hi all, I have question regarding to heater I want to build. It suppose to be a heater used for soldering a thin copper sheet (1mm thick) with other small copper components. Heater has to be flat as much as possible and reach the temp up to ~250C (solder melting point). The copper sheet...

Hi, Killing equation in flat space is just \partial_{\mu}K_{\nu}+\partial_{\nu}K_{\mu}=0 . I've seen in various places the solutions to this written as K^{\mu}=\Lambda^{\mu}_{\nu}x^{\nu}+P^{\mu} where P is a constant 4 vector, and \Lambda_{(\mu\nu)}=0 (i.e. symmetric part vanishes and it is...

..that went an infinite distance in all directions: What would it look like? Would you technically be able to see all (or a lot) of it? (speed of light permitting) It's just a question that has been bugging me for a while.

Homework Statement Hey guys, I was just wondering how do the beliefs of the Flat Earth Society defy against modern day physics? I'm doing a discussion board post for my physics class. I know they strictly do not believe in gravity but what else do they do against? For example about Newton's...

Hey there I'm wondering why it's remarkably more exhausting to ride a bike with a flat tire, compared to a bike with a hard inflated tire. The friction force "killing my efforts" so to speak, should be the same; the normal force is the same (my mass doesn't change), and the friction...

Hello, I read that when a manifold has a flat metric, the geodesics are always straight lines in the parameter space. I have two questions: (1) If we are given a Clifford torus S^1 \times S^1 (which is flat), how do we compute the geodesic between two points? Is the following correct...

Homework Statement In a Young's double slit-type experiment using light of 600 nm with 0.5 mm between fringes, a thin plate of glass (d = 100 micrometers, n =1.5) is placed over one of the slits. What is the lateral fringe displacement on the screen? 2. The attempt at a solution To be...

In another thread, https://www.physicsforums.com/showpost.php?p=2973770&postcount=45, some questions came up about what the conditions are for a spacetime to admit flat spatial slices, and for a spacetime to have a time-independent "scale factor" (see definition below). These questions...

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...

Imagine the following scenario: There is a hollow steel cube. I cut the top facet off so that I get a box with a lid and then polish both cut surfaces so that geometry fits almost perfectly (no gaps are larger than 1/100 of a milimeter or so - or even smaller). Then I close the box and...

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...

Homework Statement We wish to size a flat plate collector to provide water for one hot shower per hour. We have determined that a shower uses 80 liters of 40°C water that has been heated from a 15°C supply line. The receiver temperature must be greater than the desired water temperature of...

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

Hi all, a flat intersects with unknown tilt angle a Cartesian coordinate system into it's origin. Let's suppose the flat "rising" from negative Z values. We know: - vertical angles between flat and X, Y axis, let's suppose 10° each; - horizontal angle between tilt direction and axis. Because...

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...

Sorry if this ends up being a naive question, but I have just a little conundrum. I'm dealing with curves in R2 and the Gauss-Bonnet theorem is a very useful result with what I'm currently doing, what with Gaussian curvature of a flat surface being zero, which is all fine...

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...

i was given this question, and i can only guess at what the answer is. here it is when correcting observed images, why are multiple dome flats (flat field) combined to make a master flat field? i know how this is done, but i can't find anything to tell me why it is done. i would presume...

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...

Sound intensity on a "flat earth" Homework Statement Consider a flat Earth with an atmosphere that descreases in density as altitude increases such that rho = rho0e-h/H where rho nought is the density of air at zero altitude and H is a constant known as the "scale height". Assume the bulk...

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).