Recent content by avorobey

Thanks you! - but I yearn to understand why I don't need to worry about the constraining forces. If I solve the problem the way you're saying, then I'm ignoring these forces when I'm writing down potential energies; what is my justification for doing so? After all, they're just forces acting on...

Homework Statement This is Exercise 1.19 in Goldstein's Classical Mechanics 2nd edition. Self-study, not for a class. Two mass points of mass ##m_1## and ##m_2## are connected by a string passing through a hole in a smooth table so that ##m_1## rests on the table and ##m_2## hangs suspended...

But ##F_{ji}## depends (in general) on the position of particle j as well as i, right? If particle j changes position as the system moves from state ##1## to state ##2##, then the integrand depends on both ##{\bf r}_i## and ##{\bf r}_j##. But then, if the integral is simply over the path of...

I'm reading Goldstein's "Classical Mechanics", first chapter, and am confused about what's going on in equations of forces and work in systems of particles. For example, Goldstein calculates work done by all the forces, external and internal, in evolving the system from state ##1## to state...

Have been trying to better understand how batteries work. Forgive me if the question's naive. A half-reaction on one of the electrodes in a battery produces free electrons (for example) and consumes anions (or produces cations). I understand why, if there's an external wire for electrons to...

>Not directly, but transmitted through the lower block What exactly does this mean, "transmitted"? Microscopically?

I think I understand how pressure works with gases. More molecules bouncing around -> more random impacts -> stronger force. But I realized to my embarrassment that I don't understand how solid things press on each other, microscopically. Say I put a block of iron on my head. If I put...

I've been trying to understand what happens on a microscopic level - in terms of charges and EM fields - in a simple circuit (say a battery with wires to a lightbulb), and I'm finding it pretty difficult. I read these articles that try to untangle the flow of charge from the flow of energy, and...

Right, I understand this. What I meant is, about the most typical thing that I see done with two tensors in Wald's book so far, is multiplying them and contracting the product on one of the indices. For example, this is done all the time to raise/lower indices using the metric; but while I...

I'm trying to teach myself GR from Wald's General Relativity, and it's very tough going. I do have basic knowledge of differential geometry, but I think my geometric intuition is next to nonexistent. I'd very much appreciate some help in understanding several basic questions, or pointers to...

First of all, thanks for the helpful answers that certainly helped me see things better. I think I understand now that L is supposed to be a function of e.g. q and q* considered independent variables. What I don't understand is how Goldstein gets there. In his derivation of Lagrange's...

I'm trying to read Goldstein's Classical Mechanics (self-study), and getting into difficulties understanding the formalism early on. I thought I had an adequate understanding of basic calculus, but apparently not! Given that q* (I'm using an asterisk to denote a dot) means the derivative of...

Many thanks for your replies. I think I understand it much better now.

I'm reading through Feynman's lectures, and just read his demonstration that: a) a sphere generates the same gravity force on a body outside of it as if all its mass was concentrated in its center; b) on the other hand, on a body placed inside the same sphere there is no gravity force at all...