Surface Definition and 1000 Threads

The HadCRUT4 global surface temperature anomalies in tabular form include confidence intervals. The GISS surface temperature data is available in tabular text form here http://data.giss.nasa.gov/gistemp/tabledata_v3/GLB.Ts+dSST.txt - but it doesn't include any confidence intervals. Can...

What is the "plane of symmetry", "zero velocity wall" and "free surface" terms which I have seen in Polyflow? It says in Vnormal=Fs=0 for plane of symmetry and Vnormal= Vs= 0 for zero velocity Wall. Now I get when Vs=Vn=0 it means that the wall isn't moving and it's in a static state but didnt...

Homework Statement How do I find the surface area of a sphere (r=15) with integrals. Homework Equations Surface area for cylinder and sphere A=4*pi*r2. The Attempt at a Solution I draw the graph for y=f(x)=√(152-x2). A circle for for positive y values which I rotate. I will create infinite...

Homework Statement Compute the average number of molecular hits, per unit time, experienced by a square inch of surface exposed to air, under normal conditions. Assume air is a mixture composed of 80% N2, 20% O2, both of which are assumed to be ideal gases. You will have to perform angular...

Homework Statement The plane with surface charge sigma lies in x-z plane at y=0, parallel to it at y=a there is a grounded plane. What is the field just above the bottom plane, find the potential between the planes Homework Equations discontinuity E=sigma/epsilon, V=Qd/Aepsilon take the...

We are currently trying to measure pH levels on the (wet) surface of metals as part of a study about corrosion. The surface may have a non-conductive protective layer. - is it feasible to measure pH on a planar surface (dry or wet)? Which kind of sensor probe can be used for this task? -...

I was just looking through a few different solutions in Griffiths EM and I must have not realized it, but do bound and free charges both contribute to the overall electric field? For example: when dealing with a capacitor with a dielectric between it, one of the solutions wants to find the...

Hello guys, Consider a partially filled tank with water where the acoustic field can be described by the Helmholtz equation. The boundary condition at the water surface would be \frac{∂p}{∂\vec{n}} = -j\rho_0\omega\frac{p}{Z} where Z is the impedance of the water surface. What would be...

Hello guys! I have to model the acouctic field within partially filled cavities. So consider a rectangular or cylindrical cavity that is partially filled with water. I would like to model the water layer as a sound absorbing wall by prescribing it as a surface impedance boundary condition...

Homework Statement New to physics forum, so please forgive me if I am posting this in the wrong place, but it seems to me that this is a homework-type or basic physics question. Here it is: You have a perfect cube with substantial mass sitting on a flat frictionless surface. The surface plane...

Homework Statement A cylindrical container of water with a radius of 6.0 cm is placed on a phonograph turntable so that its outer edge just touches the outer edge of the turntable. The radius of the turntable is 14.5 cm, and the turntable rotates at 33 and a 1/3 revolutions per minute. How much...

Homework Statement A child stands on frictionless ice and throws a snowball. Estimate the recoil velocity of the child. Homework Equations m1v1i + m2v2i =m1v1 +m2v2f 1/2mv21i + 1/2 mv22i = 1/2 mv21f + 1/2mv22f The Attempt at a Solution After choosing estimates for weight of snowball, speed of...

Homework Statement Wikipedia tells me that I can obtain the surface area of a sphere by realizing that the volume of a sphere is equivalent to the infinite sum of the surface areas of hollow, nested spheres, sort of like little Russian dolls. That makes sense, and then differentiating both...

Homework Statement A 3 m long gate of weight 4 kN per unit width is hinged at O and sits at an angle θ as a function of water height h above the hinge. (A) Using a y-axis measured up from the hinge, derive a general relation between h and θ, with all other variables evaluated in the relation...

Hi everyone. I'm looking for some help from someone expert in optics to create an inteferometry based setup to map the surface of a small object. This is for a small lab project so I'm not looking for a really complex setup, I just need something simple that can be built in a short amount of...

Homework Statement [/B] Homework Equations ##\vec{E}##=##\frac{∂V}{∂r}## The Attempt at a Solution I have provided both problem and solution(almost)but the problem is I did not understand the solution.First of all I did not understand the question what we are told to determine? I locate the...

Homework Statement \vec J_b = 3s \hat z \int \vec J_b \, d\vec a I need to solve this integral in cylindrical coordinates. It's the bound current of an infinite cylinder, with everything done in cylindrical coordinates and s is the radius of the cylinder. The answer should end up with a phi...

Hi, I've been doing reading on Halbach Arrays moving over surfaces and generating repulsive forces. From my understanding, the moving magnet induces a circular electric current in the metal track, which gives rise to a magnetic field. However, I'm having trouble understanding why this field...

We just started going over line integrals in calculus, and have been told that the integral over any closed surface is 0. What I don't get is then why can we do the line integral of a circle to get 2##\pi##r? Since a circle is a closed surface, shouldn't the line integral then be 0?

I have recently had a series of lectures on X-ray physics. I have been quite confused by the concept of effective dose and entrance surface dose. I have been told that entrance surface dose varies proportionally to kV squared. I have also been told that as kV increases, effective dose...

Hi, I am trying to get some information about why Matt black surfaces are such good emitters and shiny surfaces are not. When you try and look this up there really isn't much so I have tried to string what I have found together. Shiny metal surfaces have free electrons which cancel the...

1. Introduction Pressure of a fluid exerts thrust on each part of a surface with which the fluid made contact. Each forces distributed over the area have a resultant magnitude and direction that is very crucial. For a horizontal surface, the pressure does not vary over the plane. Thus, the...

Homework Statement Calculate the integral ##\oint_C \vec F \cdot d\vec S##, where ##C## is the closed curve constructed by the intersection of the surfaces ##z = \frac{x^2+y^2}{4a}## and ##x^2+y^2+z^2=9a^2##, and ##\vec F## is the field ##\vec F = F_0\left( \frac{a}{\rho}+\frac{\rho^2}{a^2}...

I'm trying to deduce the differential equation for temperature for a triangular fin: I know that for a rectangular fin, such as: I can do: Energy entering the left: q_x= -kA\frac{dT(x)}{dx} Energy leaving the right: q_{x+dx} = -kA\frac{dT(x)}{dx} - kA\frac{d² T(x)}{dx²}dx Energy lost by...

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)

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...