Recent content by penguin46

I am fairly certain that the answer here is to differentiate partially with respect to time rather than fully. In Landau and Lifshitz' proof of energy conservation one of the hypotheses is that the partial of L wrt time is zero. Am I on the right track?

i don't know that equation

yeah sorry dude i give up

A*dP

force of gravity, outside pressure, inside pressure. only inside pressure changes

i have no idea, none of this makes any sense. How am i supposed to know whether the question writer wants me to take that into account? i have thought about this question for like 3 hrs now and still don't even know where to start

well the net force would be equal to pressure x area, and so we would calculate how much the pressure changes based on a small displacement? it is vertical

It should be non-zero force because the pressure depends on volume, right? I would say it should be adiabatic, because it is probably moving too fast to be isothermal.

Hi, this is a question from my textbook that I can't quite make sense of. I don't really know where even to begin, to be honest. The only thing I can think of is that the bead is at equilibrium, thus the force of gravity is equal to the pressure exerted by the gas. I don't know where the heat...

Okay. First of all, thank you for the help so far. Second, so when doing questions such as these, you simply have to find which of the coordinates the Lagrangian is independent of? I suppose that does make sense. Third, in the beginning of Landau and Lifshitz they kind of treat time invariance...

(b/c)^2*zdot^2*sin^2(z/c) + (a+b*cos(z/c))^2*phidot^2 + zdot^2

okay So i got L = rdot^2 + r^2*phidot^2. Is that correct? I really should brush up on taylors book because a lot of this is vague to me. No idea what to do next. The book we are using for my course now is landau and lifshitz btw, but he does deviate from it (for noethers theorem e.g.)

Well then zdot would ust be zdot and ydot would be rdot*sin(phi) +r*cos(phi)*phidot. But isn't that what you told me not to do? Because doing this will just lead to a very big equation once you put sub in the expression for r and square every term

My professor was explaining this today and tbh I'm more confused than I started out. He did something with Noether's Theorem? I don't understand any of it. I have an exam on this next week.

I don't know how to do this So that would be the radial angle, right? But shouldn't there be 3 integrals of motion for a system with 2 degrees of freedom?