Lecture 7 | Modern Physics: Classical Mechanics (Stanford)

[mar77a]

At about 1:43, he actually gets -Bx and -By. My guess is that when he set up the Lagrangian he put +V instead of -V for the potential, in this case magnetic vector potential. So he ends up with -(v x B) instead of (v x B).

It'll be nice if someone can confirm this.

[mar77a]

@mar77a Nvm that, the whole L = T-V thing is a mnemonic. I was just reading about this in Shankar and the EM Lagrangian he uses is correct. For more info check "R. Shankar - Principles of QM, page 83".

[grunder20]

Thumbs up Susskind!

[Braskass]

I am studying Physics in Germany and this lecture helped me a lot! I can't find any electrodynamics Lecture. He didn't give one? :(

[insparato]

avocadomilk: No, he means divergence. Divergence gives you a scalar, you're doing the dot product of of del and a vector hence scalar. Gradient gives you a vector.

[avocadomilk2010]

round about 39mins, he really means the gradient, not divergence no? divergence results in a vector, while he's got a scalar there.

[MichaelKovarik]

I have been trying to look for sources to back up Susskind's claim that a quantum particle cannot be localized into a region with an area of the reduced Planck's constant, 1.05(10^-34) Joule-seconds. However, I couldn't find anything to back it up. Can any of you show me sources to back up his claim?

[qftftw]

@MichaelKovarik He's not talking about localizing a particle's position in space, but its simultaneous position and momentum in phase space. A minimum phase space area of hbar implies delta p * delta q >= hbar, which is basically just a geometric interpretation of the Heisenberg uncertainty principle. Why he writes hbar instead of hbar / 2 for the area is unclear to me, but it may just be a simplification.

[Ferrus91]

Still questions about friction! Gah!

[ClamCrunchy]

Fractals are continuous functions but not differentiable, so why can the phase space volume evolve into fractals?

[03Kabbotta11]

@ClamCrunchy It never becomes completely fractal. It only begins to become more and more fractal-like. The continuity will remain until an infinite amount of time had passed.

[RobotTed]

The stripped shirt! It's back!

Yay! :D

I was worried he lost it. Totally math!

[the1prevailer]

I am not being able to download the movie , when I press the download button it gives me an error and the page dosent load?!!!

[beenpimped31]

I love classical mechanics, this class was one of my favorite and most exciting classes as an undergrad.