Surface Definition and 1000 Threads

Hello ! Homework Statement In an exercise we consider two surfaces given by f1=(x,y,f(x,y)) defined in a domain D And f2=f1 in D' And a line d with two parametrizations d1=(f(y,z),y,z) d2=(x,f(x,z),z) They ask to find the principal curvatures of S1 U S2 U d Homework EquationsThe Attempt at a...

I'm confused what the difference between the two are...I thought surface brightness was luminosity, but apparently it's not: L=Surface brightess x Area...But I came across a similar equation that seems to assume surface brightness is the same as apparent brightness. Please help! Edit: Also, why...

Can anybody explain under what conditions does this happens? Why does the light beam travel on the curved surface? How does this happen? Isn't light suppose to travel in straight line?

A Cauchy surface is a 3d spacelike slice of spacetime. Could you read the definition (17) p18 the author says that "one can proove that ##\sigma## does not depend on the choice of the Cauchy surface because the functions obey the law of motion." Could you elaborate? Thanks Could anyone add "h"...

Homework Statement Find the point on the surface z2 = xy + y + 3 which is closest to the point (1,2,0)Homework EquationsThe Attempt at a Solution Can someone check my work?

Hey guys! What would be the gravitational effect of Earth on it's surface, if somehow the density of mass was uniform and equal to 2/5 of the real value? Assuming that the size e shape os the planet doesn't change.

Hi, So for a piece of maths coursework I am thinking of trying to calculate the surface area of an atom or molecule. I do not know whether it would be viable because there isn't a clear boundary for an atom/molecule due to the electron clouds. However I wanted to know if I could do something...

Homework Statement A 3.0 kg block is held against a spring with a force constant of 125 N/m. The spring is compressed by 12 cm. The ice is released across a horizontal plank with a coefficient of friction of 0.1 A) Calculate the velocity of the block just as it leaves the spring. Assume the...

Homework Statement A 100N box is initially at rest on a rough horizontal surface. The coefficient of static friction between the box and the surface is 0.6 and the coefficient of kinetic friction is 0.4. A constant 35N force is aplied to the box horizontally. Identify from choices (a) - (e)...

Hi, I have an mathematics assignment to do, and I wonder if the topic I have chosen is doable for me. I want to minimize the surface area of a cobbler cocktail shaker, and until now my plan was to get the curve equation for the side of it, and get the area equation from surface of revolution...

Not sure if this is an engineering or physics question, but here it goes: I'm trying to wrap my head around the pressure field caused by waves. I'll recap to so anyone can check if I have made any incorrect assumptions: If we ignore atmospheric pressure, the pressure in the water has a...

Homework Statement Find vector normal to z = x^2 + y^2 - 3 at point r = (2, -1, 2) Homework EquationsThe Attempt at a Solution here is the markscheme. I understand how to find the gradient, but i don't understand how they calculated the magnitude. thanks

Homework Statement This example is from 3rd edition of Griffiths' textbook. Ex. 5.8 on page 226 I understand that by reversing the direction of the current, sign of B is switched. but i can't get it that highlighted part. and why B doesn't have z-component? Homework EquationsThe Attempt at...

Consider the Lindhard response function: \chi(\vec{q})=\int\frac{d\vec{k}}{(2\pi)^d}\frac{f_\vec{k}-f_{\vec{k}+\vec{q}}}{\epsilon_\vec{k}-\epsilon_{\vec{k}+\vec{q}}} where ##\vec{q}## is the wavevector, ##\epsilon## is the free electron energy and ##f## is Fermi-Dirac distribution function. For...

This is more complicated than it sounds. I'd like to analyse a fracture in a surface body so I need to create a no thickness or infinitesimally small cut/slice if it is possible. Afterwards, I'm planing to analyse stress concentration factor in model environment.

Homework Statement Homework EquationsThe Attempt at a Solution Working from the reference frame of block , a pseudo force Ma0 towards right need to be applied on the cylinder . Forces acting on the cylinder are pseudo force , weight Mg and normal force from the block (if any) . Since the...

Homework Statement Find an equation for the tangent plane to a surface xz^2 +x^2y-z=-1 at the point (1,-3,2). Homework Equations (\vec{r}-\vec{r_p}) \cdot \nabla f(\vec{r_p}) = 0 The Attempt at a Solution [/B] First I found the gradient of the function \nabla f = (z^2+2xy)\hat{i} + x^2...

Suppose a block of 5kg is stationary on a table with μ_{s} = .15 and μ_{k} = .1 μ_{s}(F_{N}) = μ_{s}(mg)= .15(5)(10\frac{m}{s^{2}}) =7.5N μ_{k}(F_{N}) = μ_{k}(mg)= .1(5)(10\frac{m}{s^{2}}) = 5NThe force applied to the block is represented by the function: f(x) =...

why there is a nodal surface in 2s suubshell ?

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)

It's pretty easy to find the "working principle" of surface capacitive touchscreen like http://www.elotouch.com/Technologies/SurfaceCapacitive/howitworks.asp Roughly speaking, I know that A surface capacitive touchscreen has a conductive layer to which some electrodes are attached The...

We need to be able wire it up to a monitor that displays where the surface is being touched. Not a huge feat. However I'd like to start buy ordering a piece a flexible, capacitive touch surface (not a screen). Anyone can assist?

In the context of surface science and materials science, what does it exactly mean when a surface is, say, "metal-decorated"? By reading plenty of journals, I am assuming that it means that the atom is adsorbed on the surface, which means that the atom that "decorates" the surface is bonding on...

Hi there, I´m reading about the theory of radiation and came up with some doubts when I started to calculate the net flux that an observer would "see" coming off from the star. I have provided my answers to my own questions but would like to see what you people think about them. 1. Can it be...

Homework Statement The flux through the hemispherical surface in the figure shown below is Homework Equations The Attempt at a Solution But the above formula is for closed surface .But hemisphere is not a closed surface to make it closed surface we will need another hemisphere . then the...

1. The trajectory of a rock thrown from a height with an initial speed of 20.9 m/s is shown in the figure below. Evaluate the magnitude of the gravitational field at the surface of the planet. The planet has no atmosphere...

Hi, I am wondering. Is it possible to predict the amount of time dilation on the surface of the sun compared to the surface of the earth? Is this a correct question to ask, or have I made a bad assumption? Thanks in advance. Ayjay

Homework Statement 9x2 − 18x + 4z2− 24z − y2 + 45 = 0 Homework EquationsThe Attempt at a Solution so let's start with the zy trace, setting x=0 we are left with: 4z2 - 24z - y2 = -45 completeing the square gives : 4z2 - 24z + 144 - y2 = -45 +144 4(z-12)2 - y2 = 99 divide both sides by 99...

I know in such type of questions we should try to enclose the charge completely and symmetrically by as many bodies requires as that of the given body. Let's say if Charge Q is kept at the mouth centre of a hemisphere .Here a hemisphere is given so we know if another hemisphere is placed below...

Homework Statement In a region of space there is an electric field E(vector E) that is in the x-direction and that has magnitude E=(663 N/(C*m))x Find flux for this field through a square in xy plane at z=0 and with side length 0.330m . One side of the square is along the +x-axis and another...

Hello, given the figure above, how do I get the tangential and normal components of a vector in any plane by integration?

in the video above the instructor explains from time 8:22 to 8:55 that how and why electric field lines going out from the surface which do not enclose charge is zero but I don't understand then why not electric field lines going out from the spherical surface ( enclosing charge) is...

Assumption: Earth is a perfect blackbody. This means that the emissivity (ε) is 1. Earth’s radius = 6371 km Incident solar radiation = 1367 W/m2 Temperature in space = 0 K I'm given the above data. I tried using the E= σεTe4 but that doesn't include the radius of the Earth :S Im really...

Homework Statement A truncated cone has smaller radius of 5 feet, larger radius of 10 feet, and a depth of 1 foot. Total volume is approximately 183 cubic feet. If I have water in there at x inches how much does the radius at the surface of the water increase per inch? Homework Equations f(x)...

The sun has no surface, but it appears to have a surface. I may recall that Feynman said that the apparent diameter is equal to the mean free path of a photon. That could be, but I don't get the relationship. Any help?

Hi Forum, Just wanted to ask how to compute surface area of a helix x =cos t, y =sin t, z=t by integration Thanks in advance.

I am a Ph.D. student just beginning my research. Recently, I found several papers about surface and interface interesting, so I want to know more about this area. However, I cannot find any specific review which can give me an overview of this area. Can anyone give me a link to such literature?

When I learned about volumes of solids of revolution, I never really memorized any formulas for specific cases per se. I used two expressions for area, either ##A = \pi (R^2 - r^2)## and ##A = 2\pi r h##. Those expressions worked for rotations about any horizontal/vertical axis (not necessarily...

MTW, p. 924, defines a caustic as a point where a null geodesic originating from the external universe enters a black hole's event horizon, remaining in the horizon afterward for some finite affine interval. (A null geodesic of this type is called a generator of the horizon.) They introduce this...

http://www.sciencedirect.com/science/article/pii/S0273117715005712 from the abstract: Obviously, the most prominent missing 'forcing' parameter here, is "concentration of greenhouse gasses". There is probably some food for thoughts here, especially when the analysis of Den Volokin and Lark...

I am confuse with the fact that current carrying conductor has gradual surface charge density which provide force to electron to produce current.

I understand how surface area does not come into the equation governing the resistance an object has to sliding. It leads one to believe that all tires would perform equally in dry conditions. Why do people then say that bald tires give better grip?

Hello, I know you can use Gauss' law to calculate the electric field of volume and surface charges but i cannot figure out a way to do it using Coloumb's law. I have several questions about this: when you integrate the charge density in Coloumb's law over the volume is the r^2 inside or outside...

Homework Statement Determine a simplified, factorised expression, in terms of the radius (r), for the surface area of a cone where diameter (D) = perpendicular height (h) Homework Equations A = πr (r + √(h^2 + r^2)) The Attempt at a Solution h=D=2r A = πr (r + √(2r^2 + r^2)) A/π = r (r +...

Hi all,If there is activation energy for chemisorption, then an atom with insufficient energy to overcome that barrier will remain physisorbed to the surface via van der Waals forces. I would like to further understand this activation energy in terms of, for example, the overlap of electron...

Homework Statement You've probably noticed that TV screens and computer monitors have an annoying tendency to accumulate dust. Wanting to understand this better, you decide to model the situation as follows: you assume a small mote of dust might have an excess charge of 1 nC and a mass of 5...

Homework Statement I am attempting to replicate the IPCC estimates of the amount of sea level rise due to thermal effects on the seawater. The earth, black-body temperature is 16C but there are projections of a 1C increase in less than 100 years. Ignoring ice melt and land flooding, how much...

How would I go about finding temperature distribution in a thin square plate during the the first few milliseconds (or actually a fraction of a millisecond) after t=0s. Initial temperature distribution throughout the plate is known, there is heat flux to one side = Qinj, while heat flux from all...

Hello, I've just read and I think I have understood the following result : If we were to geodesically transport all points of a small 2D surface, so small that it would be flat for all purposes, in a direction vertically above it, and if this surface belongs in an arbitrary 3D manifold, then in...

Homework Statement A match of length l=4cm is floating on the surface of the water from a glass. ( the water is at room temperature) If from on one side of the match we pour a few drops of soap, the match starts moving. In which direction is the match mooving and what force is acting upon it? (...