What is Flat: Definition and 495 Discussions

Homework Statement hi I'm trying to design a small experiment based on soil pressure i've not had much use of some of the equations and principles for a few years so I'm a little rusty basicly I'm trying to exert pressures onto grass seeds (lolium perenne) in a rough field experiment in...

There is a video on youtube called how do we know the universe is flat. (put those keyword in youtube and you should find it, I can't post links to videos until I have 10 posts) It has something to do with using the Earth as an apex of a triangle then measuring two points on the cosmic...

I was trying to think of QM in the context of different possible spatial curvatures since the standard cosmology (FRW model) admits at least in principle that 3-space can have positive, negative or no curvature, even if the flat space is favored by the CMB WMAP-COBE observations etc, when I...

Homework Statement Two flat charged plates create a uniform electric field (E). What happens to voltage (V) when the distance (d) is doubled? Homework Equations Voltage in uniform electric field: V = E*d Capacitance equations: V = Q/C C = K * A/d The Attempt at a Solution...

I am trying to calculate the moment of inertia of a formed (uniform curve) flat bar. I have attached a sketch . The bar is 5/8" thick x 1" wide. I'm stumped.

hi, I am a bit confused on what the current model of the universe is. some are saying it is round, while others are saying it is flat. which is true? If the universe is flat, then is it that only some part of it is flat or the whole universe is flat? how can we prove it theoratically...

for estimating Pn...

I'm asking because some of you state that flat spacetime can't model black holes... meaning even between the Planck scale and event horizon, but yet atyy said spin-2 field in flat spacetime is equivalent to General Relativity for spacetime that is covered by harmonic coordinates which atyy...

It is said that minkowksi spacetime is flat. How about galilean (Newtonian) spacetime, is it flat too? If not, what is it? It is also said that it is unknown whether there is geometry or spacetime inside Planck scale. If there is none. I can't imagine how the Planck scale without geometry can...

Hi, does flat spacetime + gravitons automatically lead to curved spacetime? In an old 2002 google thread sci.physics.research which is moderated...

Hi, I would like to get suggestions about the physical meaning of the (1) flat-band voltage and the (2) Fermi-level. Before being marked as newbie, I'd like to point out that I know how to calculate them and know that the (1) flat band voltage is the one which you apply, the energy band...

I'm uneducated in Physics so I'm not sure where to begin with this. I want to build a vacuum chamber that is rectangular and fairly flat. It will measure 48"X96"X8" I plan on constructing it from clear polycarbonate sheet on one face (would clear acrylic be a better choice?) and aluminum sheet...

Just a introduction to my project, I have designed and building a 69 Volkwagen Bug with a Version 8 subaru Sti Engine, The pan is built with tube braces and coil over suspension, I built a tall back bone frame for strength and for the rest of the frame to be lower for ride height and suspension...

Homework Statement Two identical flat capacitors with no dielectric material inside are connected in series to a voltage source. The electric field intensity inside the capacitors is E. If the space inside one of the capacitors is filled with a dielectric material of ε=9 how strongly did the...

"Flat Universe"question. Hello, everyone! I'll start by saying that astronomy or physics are not my majors here; I'm a freshman Med School student, however I've recently started amateur astronomy as a hobby. Naturally I had to increase my knowledge on this subject so I started visiting...

Hi there. I have a current I running throught a tesla spiral coil, and I have to compute the magnetic field at the center of it. The tesla coil has N turns, and an inner radius a, and outer radius b. This is the tesla spiral coil: The courrent enters through the outer cable, and goes out...

I'm writing a paper for a philosophy elective on the Cosmological argument. One of my counter arguments is that a causal loop (treated as a paradox in the Cosmological argument in favor of a creator) is not a paradox if time is cyclic in nature rather than linear. I treat the fact that the...

Is the following true ? In flat space, we have a familiar doppler shift formula for two observers moving relative to each other. Suppose they had a relative ,constant acceleration between them.Then their relative velocity is changing with time. Will the doppler shift formula still hold with a...

Nice article in 'The Economist' on how Republican candidates are competing to race to the lowest point: http://www.economist.com/node/21534799 With a candidate Romney/Cain/Perry and all their lunatic tax reform proposals, I can not possibly imagine how the Republicans will beat Obama next...

Homework Statement Establish the theorem that any 2-dimensional Riemann manifold is conformally flat in the case of a metric of signature 0. Hint: Use null curves as coordinate curves, that is, change to new coordinate curves \lambda = \lambda(x0, x1), \nu = \nu(x0, x1) satisfying...

Homework Statement Is a spring longer hanging or flat on a table? Homework Equations logic. The Attempt at a Solution I think the answer would be hanging because then the mass of the spring pulls it down a bit, thus stretching it more than when it is flat.

Homework Statement Two blocks mA= 5.0 g and mB= 10.0kg are connected to a string. Both blocks sit on a smooth inclined surface where the angle on the inclined plane is 30.0°. Block A is about block B on the incline. Find the acceleration of the system of two blocks. What is the tension TB in...

Homework Statement A nearly flat bicycle tire becomes noticeably warmer after it has been pumped up. Approximate this process as a reversible adiabatic compression. Take the initial P and T of the air (before it is put into the tire) to be 1.00 bar and 298.0K. The final volume of air (after it...

Homework Statement See figure attached. Homework Equations The Attempt at a Solution My professor came up with this example in lecture and the way he went it about it was very confusing so hopefully you guys can help me clear up some of steps/thought process he took. We are...

Suppose that you have a sheet of copper that carries a surface charge of \sigma on each face. The electric field just outside of each face can be calculated by plane symmetry and the solution would take the form E=\frac{\sigma}{2\epsilon_{0}}\hat{n} correct? If not I have to go back and...

Homework Statement In this flat plate heat exchanger, rippled plates (0.3 m thick each) create channels that allow heat transfer between a hot and a cold fluid. Conduction occurs then from the heat temperature difference between the two fluids while convection occurs as the fluids move...

Homework Statement Consider an infinite thin flat plate with a 1m chord at an angle of attack of 10 degrees in a super sonic flow. Describe the angle theta between the Lift and Normal Force, is it the same as the Drag and Axial? Homework Equations L=Ncos(a)-Asin(a) D=Nsin(a)+Acos(a)...

Homework Statement In a laboratory experiment two spherical balls are launched on a °at surface. Both are uniform spheres of radius R and mass m. They are both given the same amount of initial kinetic energy K0. However: -ball A rolls without slipping -ball B slides without rotating...

Homework Statement The mass of the homogeneous flat plate is 50 kg. Determine the reactions at the supports A and B. I've attached the diagram. The Attempt at a Solution I know I will need to find the center of mass. I don't remember exactly how to do it, but I found the centroid...

trying yo figure this out: the graph of stress concentration factor K for flat bars with a circular hole geometries are shown in the diagram link below. a load of 50kN is applied to the plate. the width of the plate b=100mm with a thickness of t=10mm find the maximum stress for the...

Hi, I'm trying to carryout some analysis of flat plates subjected to hydrostatic water pressures however the plate material is HDPE. The problem I'm having is that all the formulae on the web and in Roark's 7th Edition are typical of steel with a Poisson's ratio of 0.3. I can't therefore...

Hi there! I'm new here and am currently looking into the Hartle-Hawking and Hawking-Turok Quantum creation models. What I've read about the Hartle-Hawking model is that it predicted a Closed Universe. But isn't that the opposite of what we have learned? The WMAP sattelite has confirmed the...

Let us consider the General Relativity metric: {ds}^{2}{=}{g}_{00}{dt}^{2}{-}{g}_{11}{{dx}_{1}}^{2}{-}{g}_{22}{{dx}_{2}}^{2}{-}{{g}_{33}}{{dx}_{3}}^{2} ---------------- (1) Using the substitutions: {dT}{=}\sqrt{{g}_{00}}{dt} {dX}_{1}{=}\sqrt{{g}_{11}}{dx}_{1}...

I read that most scientists believe that the Universe is either infinitely flat or pringle-shaped flat, and that doesn't make sense with me. I don't understand how our 3 dimensional world could be a part of a 2 dimensional universe.

Homework Statement Consider a flat FRW model whose metric is (in polar coordinates) ds^{2} = -dt^{2} + a^{2}(t)[dr^{2} + r^{2}d\theta ^{2} + r^{2}sin^{2}\theta d\phi ^{2}] where a(t) is the scale factor. Show that, if a particle is shot from the origin at a time and with velocity t_{0},V_{0}...

Sorry quick question from the ignorant (of maths or physics) but what does it mean to say that the universe is flat? I assume this does not mean it only has two dimensions! I do understand that it means that it has neither negative nor positive curvature, but what exactly does it mean in...

I am studying topology. There I learn that the open sets given by the metric can be used to define a topology, e.g. the usual metric topology on R^n given by the Euclidean metric. Now I try to understand the topology of (flat) spacetime. Is there a metric? The Lorentz 'metric' gives...

Could someone clarify, and/or point me to some reference on: Lorentz metric is not really a metric in the sense of metric spaces of a topology course since it admits negative values. If I use it to define the usual open sphere about a point, that sphere includes the entire light-cone through...

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...