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  1. Astrum

    Blocks and Compressed Spring

    Homework Statement Two blocks of equal mass, connected by a masslless spring of constant ##k## are on an air track. her unstreched length of the spring is ##L##. at ##t=0## block ##b## is compressed to distance from block ##a## at ##l/2## (block ##a## is pressed against a wall). Find the motion...
  2. Astrum

    Mass, String, and a Ring

    Homework Statement A mass ##m## whirls around on a string which passes through a ring. Neglect gravity. Initially the mass is at distance ##r_0## from the center and is revolving at angular velocity ##\omega _0##. The string is pulled with constant velocity ##v## starting at ##t=0## so that...
  3. Astrum

    Request a physics/Astronomy Textbook Listing

    I'm not really trying to complain, I'm just wondering if any mods actually check the Request a physics/Astronomy Textbook Listing thread. There are suggestions there from August! I think it would be nice to have the textbook listings updated every couple weeks or so. I also have a suggestion...
  4. Astrum

    A Halloween Puzzle I found!

    I found this little puzzle on Reddit a couple minutes ago: Puzzle Here I worked out the first half, but need to try the second part of "How fast a monster can we out run?". It's an entertaining puzzle, if you'd like to give it a try, don't scroll down, it gives the solutions!
  5. Astrum

    Quantum Harmonic Oscillator

    Homework Statement Compute ##\left \langle x^2 \right\rangle## for the states ##\psi _0## and ##\psi _1## by explicit integration. Homework Equations ##\xi\equiv \sqrt{\frac{m \omega}{\hbar}}x## ##α \equiv (\frac{m \omega}{\pi \hbar})^{1/4}## ##\psi _0 = α e^{\frac{\xi ^2}{2}}## The Attempt...
  6. Astrum

    Bound Currents: Why Bother?

    In Griffith's EM text, he devouts 2 pages to deriving the equation for bound currents, and for the next 4 problems, he (the solution manual) doesn't even use the equations just introduced. I question the wisdom of deriving an equation that is harder to work with than we already had...
  7. Astrum

    Solving QM-like Problem (Shankar, Coupled Mass)

    This is solving a coupled mass problem using the techniques used in QM, it's in the mathematical introduction of Shankar. This equation was obtained by using the solution for ##x(t) = x_i(0)cos(\omega _i t)## and plugging it into ##\left| x(t) \right \rangle = \left| I \right \rangle x_i...
  8. Astrum

    Adding a Thumbnail to Google Chrome (Manually)

    Is there any way to manually add a thumbnail to the Google chrome "new tab" tab? I HATE how it won't let you pick which sites you want there, it instead makes the decisions for you. Is there someway to edit the code, perhaps?
  9. Astrum

    Differential Equations for Physics

    My weak spot in math is certainly DEs, I find them pretty boring, and fairly unattractive from an aesthetic point of view. I've spent some time with them while studying harmonic motion, and I've gotten OK at them when applied to this particular topic (aside from having trouble with solving...
  10. Astrum

    Electromagnetic Simulator

    Is there any program (preferably free) that simulates electromagnetic fields and their interactions with charged particles? I've found a couple gravity simulators, but none for EM, which isn't any fun, because I reckon it would be great to play with a realistic EM program.
  11. Astrum

    Stoke's Theorem - Curl of a Magnetic Field

    Griffiths's proof of Ampère's Law was probably one of the ugliest things I've seen. All that product rule, integration by parts and what not, really could have brought tears to the eyes of ANY man. I mean, have you LOOKED at this? GAAAAH it's terrible, really, terrible. The simple statement...
  12. Astrum

    Coupled ODEs - Applied to EM

    Homework Statement Solve the equations of motion ##\ddot{y}= \omega \dot{z}## and ##\ddot{z}= \omega (\frac{E}{B}-\dot{y})## Homework Equations The Attempt at a Solution Integrate the first equation to get ##\dot{y}=\omega z + c_1## and plug into equation 2: ##\ddot{z}=\omega...
  13. Astrum

    Intro to QM Text

    What is the best intro to QM? I was settled on Griffiths, but it seems there are only two kinds of people in this world, those who recommenced Griffiths, and those who strongly don't recommended it. I'll give a bit of background, so I can get the best possible recommendations. I'm...
  14. Astrum

    Change the Math Script Command!

    I know that you can use two ## to use inline text, but I'm not sure how to use the display mode, instead of having to write "[tex][/itex]" every time, which drives me insane. Is there some other command that I'm inaware of? Or is there simply no script to use display without writing out the...
  15. Astrum

    Electric Field of a Polarized Sphere with Nonuniform Polarization

    Homework Statement A sphere of radius R carries a polarization of \vec{P} = k \vec{r}, where k is a constant and \vec{r} is the vector from the center. Find the bopund charges, and the field inside and outside the sphere Homework Equations - \nabla \cdot \vec{P} \sigma _b = \vec{P} \cdot...
  16. Astrum

    Bound Charges - Polarized Distributions

    The potential due to a polorized distribution is given by: V( \vec{r}) = \frac{1}{4 \pi \epsilon _{0}} \int _{V} \frac{ \hat{r} \cdot \vec{P} ( \vec{r}')}{r^{2}} dV After working some voodoo math, this is worked into the form V = \frac{1}{4 \pi \epsilon _{0}} \oint _{S} \frac{1}{r} \vec{P}...
  17. Astrum

    Elemental iodine from Potassium Iodide - Reaction Equations

    In the reaction to get I2 from an aqueous solution of KI. The process. Take the aqeuous KI, and pour concentrated hydrochloric acid, followed by hydrogen peroxide. K++I-+H++Cl-+H2O\rightarrow KCl + HI + H2O The reaction with H2O2 is perplexing. I'm a physics student trying to do...
  18. Astrum

    Preparing for UnderGraduate Research

    I'm interested in getting some research under my belt starting during the 2014 academic year. What should I study over the next year, so I can try and get some research in right away? The obvious ones: Undergrad QM, EM (in the process), Class Mech (doing Morin now, the questions are much...
  19. Astrum

    MathJax command - Double-triple integral

    I've been trying to find the commands for a surface integral of a closed surface, Doing some searches, I've found that \oiint \oiiint are supposed to give the desired result, but they don't seem to be supported!
  20. Astrum

    Static Equilibrium and D'Alembert's Principle

    Virtual work principle states: δW = \sum^{N}_{i=1}\vec{F}_{i}\centerdot δ\vec{r}_{i} And from this, we can see that if a system is to be in equilibrium we have δW = (\sum^{N}_{i=1}\vec{F}_{1} \centerdot \frac{\partial \vec{r}_{1}}{\partial q_{1}})δq_{1} + \cdots = 0 Where did q come...
  21. Astrum

    Calculus of Variation - Classical Mechanics

    I'm reading Classical Mechanics (Taylor), and the 6th chapter is a basic introduction to calculus of variations. I'm super confused :confused: I've tried to go to other sources for an explanation, but they just make it even worse! So, let me see if I can get some help here...
  22. Astrum

    How Safe are Eclipse Glasses ?

    How Safe are "Eclipse Glasses"? Just how safe are these Eclipse Glasses? Ever since I learned that the sun actually burns holes in the retina of your eye, I've been paranoid of using any device that will allow "safe" viewing of the sun. From what I've been told, everyone has at least 3-6...
  23. Astrum

    Definition of Integral in Multiple Variables

    Dyadic Cube C_{k,N} = X \in\ \mathbb{R}^{n} \frac{k_{i}}{2^{N}} \leq x_{i} < \frac{k_{i}+1}{2^{N}} for 1 \leq i \leq n Where k = \pmatrix { k_{1} \cr k_{2} \cr \vdots \cr k_{i} \cr } I understand that N is the level of the cubes, but what does k equal? I'm having trouble...
  24. Astrum

    Forgot to Drop a Class

    Forgot to Drop a Class.... I went to a CC (two actually, at the same time), and I had signed up for an online English class, and had thought I dropped it, and I apparently didn't. I've got no idea, I'm gonna have to talk to a counselor on Monday, since that is the last day of classes (grades...
  25. Astrum

    Notation question - R^m -> r^n

    Notation question - R^m ---> r^n I've come across this notation a lot lately. I'm not sure what it really means. R^{m} \rightarrow R^{n} I can't find the place in my book where it explains it.
  26. Astrum

    The Length of a Matrix- Double Sum

    I'm really confused about the double sum given by my text book. Here's what it says: If A is an nxm matrix, its length is the square root of the sum of its squares of all its entries. \left|A\right|^{2}=\sum^{n}_{i=1}\sum^{m}_{j=1}a_{i,j}^{2} The double sum is what has me caught up...
  27. Astrum

    Biot–Savart Law

    I'm not sure I get how:\frac{\mu_{0}}{4\pi}\int_{C}\frac{I(d\vec{l}\times\vec{r})}{r^{3}} = \frac{\mu_{0}}{4\pi}\int_{C}\frac{I(d\vec{l}\times\hat{r})}{r^{2}} the r is a displacement vector in the first, and in the second it's a unit vector, but why is this so?
  28. Astrum

    Definition of Convergence

    I'm a bit confused about how my book defines convergence. Definition: A sequence {an} convergences to l if for every ε > 0 there is a natural number N such that, for all natural numbers n, if n > N, then l a,-l l < ε note, l a,-l l = the absolute value Maybe someone could give me an...
  29. Astrum

    Part-Time Job During Early Undergrad Years?

    Next year, I'll be a full time student. Due to poor planning on my parents part, the amount of money saved for tuition and other university costs is not as high as it should be. In order to avoid having to ask my father for money (which he wouldn't be too keen on giving me), I've been thinking...
  30. Astrum

    Using Upper, Lower Sum, Prove the Following

    Homework Statement f(x)=x^{2} from [a,b] Prove that F(x)=\frac{b^{3}}{2}-\frac{a^{3}}{2} Homework Equations The Attempt at a Solution Using the definition of an integral, we get: U(f,P)=\sum^{n}_{i=1}M_{i}(t_{i}-t_{i-1}) L(f,P)\sum^{n}_{i=1}m_{i}(t_{i}-t_{i-1}) for the function x2, how...
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