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  1. Astrum

    Non Native English Speakers: Can You Understand Song Lyrics?

    Holy crap, I never knew where that synth line came from. TIL
  2. Astrum

    Cathode Ray Tube

    Why not just buy one? You need to buy a power supply and a vacuum pump anyway. You sound like a hazard to yourself, I'm expecting this thread to be closed as well. PF has pretty strict rules when it comes to people (usually people that have no idea what they're doing) playing with...
  3. Astrum

    Sign of acceleration due to gravity doubt

    The sign of any vector is determined by your coordinate system. As long as you stay consistent with your choices, the physics is the same. When working with gravity in classical mechanics, it's standard to call it a force in the negative direction.
  4. Astrum

    Electromagnetic energy of a long wire

    The energy in ##\mathbf B## comes from having to do work against the back emf, this is work that needs to be done by the battery. All the work done here is from the battery (or source of the current) rather than the fields themselves. Or at least that's the way I understand it.
  5. Astrum

    Blocks and Compressed Spring

    I got the answer through conservation of momentum, but I think it was a little bit of an underhanded tactic. But it's all good, thanks for the help, you made me realize I could "cheat". I could have gotten an answer with 1/4 the work involved.
  6. Astrum

    Blocks and Compressed Spring

    I was thinking that a valuable piece of information might be that the force on A and B is ##k\frac{L}{2}##, but I can't figure out how to use it. These forces from the spring oppose each other. I can't understand why we should need to do anymore work on this, we have the EoM, it seems to me...
  7. 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...
  8. Astrum

    Prerequisites and Resources to learn Matrices

    If they're interested in something proof based, I don't think they'd have the mathematical maturity without some experience with higher math.
  9. Astrum

    Prerequisites and Resources to learn Matrices

    Typically you study calculus before linear algebra.
  10. Astrum

    Electromagnetic energy of a long wire

    You're really asking about the energy stored in E-fields and B-fields. The work to create a charge distribution (static) is ##W_e = \frac{\epsilon _0}{2} \int E^2 d\tau ## and to create a magnetic field you need to go against the back emf, so the work is ##W_m = \frac{1}{2\mu _0}\int B^2...
  11. Astrum

    Electromagnetic energy of a long wire

    Do you mean if there's a current through the wire? Or are you talking about a line charge and an external magnetic field?
  12. Astrum

    Gravitational force from a square plate

    I'm gonna go out on a limb on this one and put out what I got after quickly doing it out on paper. I didn't actually check the integral, so I'm not sure it's 100% right. You have the wrong expression for ##dm##, it should be ##dm=\rho dA = \rho dx dy##. I think this problem is easier to...
  13. Astrum

    What is the point of academic research in majors like English?

    I've been waiting patiently for years for someone to come out with a way to model the behavior of women. Unfortunately I think it's impossible to apply something logical such as math to the irrational world of human interactions. Dammit! Why can't woman be more like math? Instead of guessing...
  14. Astrum

    People not interested in science?

    I remember a group of students becoming distraught when the evolution unit was taught in HS biology. Even in a fairly educated northern state, we have our fair share of loons. I confronted them on why they thought it was BS, after telling me about "the Bible", they couldn't come up with anything...
  15. Astrum

    Mass, String, and a Ring

    I see, that makes a lot of sense. I was under the impression that I didn't need to place limits of integration on there. I'll be sure not to make that mistake again. Thanks for the help, I made that one way harder than it needed to be.
  16. Astrum

    Mass, String, and a Ring

    I tried to solve it with respect to ##t##, because that's what we're after, why would be integrate ##r##? Doing it the way you said, we find ##\omega = r + C##, and that just isn't right. My attempt is here: Solving this, we end up with $$\omega (t) = ce^{\frac{2v}{r}t}$$, solving for...
  17. Astrum

    Mass, String, and a Ring

    Sorry, I always seem to miss terms when typing them =/ I realize that, ##r\omega = v##. What does this do for us though? All it does is eliminate the very thing we're interested in finding. I don't really understand the direction you're pointing me in. Because there's no force in the radial...
  18. Astrum

    Mass, String, and a Ring

    Yes, this needs to be worked out through using force, rather than conservation of angular momentum. I'm not sure what you mean by tangential, are you talking about ##\hat{\theta}##? ##a_r =( \ddot{r}-r\omega ^2 )\hat{r}## and ##a_{\theta} = (r\dot{\omega}+\dot{r}\omega )\hat{\theta}##, these...
  19. 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...
  20. Astrum

    I really need a resource to explain the linear potential well to me

    How can you expect us to help when you don't actually tell us what you're asking about? What exactly is it that's confusing you?
  21. Astrum

    Need Equations for Ballistics!

    Welcome to PF Have you checked out the basics kinematics equations? Link If you're neglecting air resistance, it doesn't really get much more complicated. Of course you'll need to break the motion into it's components with basic trigonometry. I realize that you're probably looking for quick...
  22. Astrum

    So you are not very smart, what's next?

    What? Did you just call that grade F meat, scavenged from the local dump FOOD?! I've read too many disgusting stories about fast-food chains to ever attempt to eat there again. I'd rather eat boiled potatoes.
  23. Astrum

    Spherical Coordinates

    It appears that page is wrong. You're right, the correct relation is ##\theta = \tan ^{-1}\left( \frac{\sqrt{x^2 +y^2 }}{z}\right)##. You could also write it as ##\theta = \cos ^{-1} \left(\frac{z}{\sqrt{x^2 +y^2 +z^2 }}\right)## Edit: Darn you, jtBell, you beat me by seconds!
  24. Astrum

    Advanced physics mentor

    I think this thread is starting to derail with all this talk of dog brains. Assuming you're being 100% truthful, I can fully understand that you want a physics mentor, it really does make things easier, but you still need to put in a lot of work on your own. Work that can't be done but...
  25. Astrum

    How can i learn about physics / mathematics after graduating

    Ha, yeah, that came across wrong. Don't worry, I eye-rolled too. Reminds me of a scene from MacBeth!
  26. Astrum

    How can i learn about physics / mathematics after graduating

    I can't tell if you're being sarcastic, or just stupid. In regards to what? You already have a job set-up, and you say that you don't want to go to grad school. So what do you want us to tell you? Here's a two step solution for you. 1. Find a textbook 2. Study said textbook
  27. Astrum

    Free-fall acceleration vs gravitational acceleration

    What? You need to find the centripetal acceleration, yeah. What you have written ##ma_g-\omega^2 R## is, as you say, for when ##\theta = \pi /2##. Generalize everything, and you'll have your answer. ##a=a_g + \frac{\mathbf F _r }{m}= a_g - \frac{(\mathbf \omega \times \mathbf r )^2}{r}##...
  28. Astrum

    Free-fall acceleration vs gravitational acceleration

    Oh, I see what you're asking about. What you'd need to find is the centripetal acceleration at the surface of the earth and hence, ##\mathbf v##. Use ##\mathbf v = \mathbf \omega \times \mathbf r ## to find this, then you can plug it into the equation for radial acceleration.
  29. Astrum

    Free-fall acceleration vs gravitational acceleration

    Your post was difficult to follow, but I understand that you're confused about the "component of gravity" here. When we say ##g=9.8 \frac{m}{s^2}##, we're talking about the average acceleration due to gravity across the earth. The Earth is an oblate spheroid, which means that the distance...
  30. Astrum

    Request a physics/Astronomy Textbook Listing

    I've never actually scrolled to the bottom of a thread list for the entire year I've been here. Thanks, that helps a lot. What do you mean when you mention the availability of the requested books? Amazon has pretty much any book you can think of.
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