Flat Definition and 507 Threads

I have plotted a lift curve of a NACA 643-418 airfoil section which has a flat region in the lift curve approximately from 11 degrees to 16 degrees. Beyond 16 degrees it completely stalls. Can some explain to me the reason behind this flat region in the lift curve. The experiment was a force...

Am i right in saying that consenses amongst the cosmological community is that the curvature of space is 0? So it is flat euclidean geometric space (I hope I am using correct terminology) which is neither +/- in curvature but exactly 0? Am I also right in saying that flat cosmological models...

soo as the title says, i need formula for force acting on a plate that is moving trough fluid, in my case air... need it for rocket simulation because of its flat stabilizers... i thought like this: a flat plate is moving in any direction (yeah that complicates things... but keep it...

So if you take a sphere with coordinates (r, \theta,\phi) and keep \theta constant you get a cone. The geodesic equations reduce to (by virtue of the euler - lagrange equations): \frac{\mathrm{d} ^{2}r}{\mathrm{d} s^{2}} - r\omega ^{2}\frac{\mathrm{d} \phi }{\mathrm{d} s} = 0 where \omega =...

proving that the sphere cannot be expressed in "flat coordinates" for the sphere in R^3 i have that ds^2 = dϕ^2 + sin^2(ϕ)dθ^2. using the definition of a flat space as one where given a set of curvilinear coordinates, one can find a metric such that ds^2 = dx^2 + dy^2, how would one prove that...

Homework Statement Could anyone show me how I would go about finding all the killing vector fields for: ds^{2} = dx^{2} + dy^{2} + dz^{2} Homework Equations Requirement for a killing field: \nabla_{b}X_{a} + \nabla_{a}X_{b} = 0 (Sorry the indexes should be lower indexes but latex is messing...

Homework Statement Explain the factors that determine the parallel and normal components of the elctric field near to the surface of a flat metal plate Homework Equations The Attempt at a Solution No idea what this question wants..? Is it something to do with the smoothness of...

I am attempting to compute the integral of a function that is mostly flat relative to a few localized peaks. These peaks are the bulk of the contribution to the integral. I decided to try the VEGAS algorithm to do this. I am running into some difficulty, so I am reaching out to YOU...

Does anybody have any experimental data on flat back airfoils. I would like to know the experimental data, experimental setup and initial flow parameters etc. In case if you find it from a report I would be glad if you can give some information regarding the report, such as author, report name...

Why are solar systems and galaxies flat? I find it peculiar that astronomical clusters (ie: solar systems and galaxies) are arranged in a flat plane. Can someone explain why? I understand that: any solar system originates from a random cloud of dust and gas. This cloud will feel its mutual...

Homework Statement I am writing a MATLAB code to predict plate displacement for multiple load conditions using the rayleigh-ritz method. I have gotten the first three loads but I am struggling with the last load case. I need to represent a distributed load for a flat plate that is piecewise...

Hi, I have read Lift-it catalogue and I found out it is very professional and useful . I have some questions in the subject and I'll be grateful for professional answers. I found out that there is a direct relationship between SWL and the width of the strip (1600 lbs/in of width for nylon...

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?