Classical Mechanics | Lecture 3

(October 10, 2011) Leonard Susskind discusses lagrangian functions as they relate to coordinate systems and forces in a system.

This course is the beginning of a six course sequence that explores the theoretical foundations of modern physics. Topics in the series include classical mechanics, quantum mechanics, theories of relativity, electromagnetism, cosmology, and black holes.

Stanford University

Stanford Continuing Studies

Stanford University Channel on YouTube:

[zen-hxhn]

reading classical mechanics by the man himself and watching these videos really helps a lot, whatever i dont understand in the book i understand here and whatever i dont understand here i understand in the book, thank you stanford and Dr.Susskind.

[joabrosenberg]

Law of least (extremum) action; Calculus of variations (minimal distance between points) 11:45; Light moving the shortest time between points 21:00; Motion on a line 24:00; Action definition, Lagrangian 31:00; Euler Lagrange equation 47:00; The Langrangian that produces Newton equations 50:40; Least action does not depend on the coordinate system (unlike the equations of motion) 1:01:00; Coriolis and centrifugal force 1:16:00; Polar coordinates 1:22:30; Conservation law (angular momentum) 1:31:00

[Rakeshkumar]

To me, this is the most important lecture of the series, the way Euler Lagrange equation was derived blew my mind.

[rodovre]

I have never seen this topic explained with so much clarity. He is the greatest teacher in physics, and I admire his effort to go through all of physics for the benefit of beginning students. It is a great contribution to the field as a whole, and hopefully some of his listeners will become future physics stars thanks to this, just like the Feynman lectures.

[ButtUglyParakeet]

The textbook Classical Mechanics by John R. Taylor has many exercises that fit well with this course.

[ozzyfromspace]

1:00:20 "we have written down the law of...scones". Only at Stanford. Great lecture, Professor Susskind!

[AlphaFoxDelta]

His teaching makes me so happy, I couldn't ask for a better physics professor.

[andreamercuri]

We love you, Prof Susskind. Thank you so much for your free and marvellous lessons

[andyjiao]

Professor, you are a proper theoretical physicist that I aim to be. You do not make over-arching assumptions, and promises the integrity of theory.

[jessstuart]

1:06:25 "That's correct, you can check this." I did, and it isn't correct.

x = X*cos(ωt) - Y*sin(ωt)
y= X*sin(ωt) + Y*cos(ωt)

[VladTepesh]

Looks like this is helpful if the actions are not only passing through a void or vacuum, but also when the actions transition between states of matter / elemental compounds from a to b. Like how the action of light passes through air, and transitions through water does not appear to be a straight line, but rather a path of least action such that it goes the distance from a to b in the least amount of time with respect to the transition between states of matter / elemental compounds.
Very cool!

[benjamincordes]

Great lecture, thanks so much for sharing this. I found this very helpful and well explained.

[xhonshameti]

So Concise! He Knows and feels the fabric! Beautiful!

[TheGaminggk]

Watch out at 1:06:00 guys. Its a rotation matrix basically. The equations are actually x = Xcos(wt) - Ysin(wt) and y= Xsin(wt) + Ycos(wt)

[tshankomakech]

the concepts are well explained in his lectures for every one to understand, thanks for this lecture i appreciate it

[joelcurtis]

Very insightful derivation of Euler-Lagrange equations. Much in the style of EF Taylor. Much more intuitive than the typical textbook presentation that relies on integration by parts.

[DrDress]

12:00 calculus of variations
45:00 E-L discrete derivation

[jsh]

One slightly confusing notational point: In his derivation of the Euler-Lagrange equations (around 44:00), he keeps writing del L / del v_i and del L / del v_{i+1}. But L itself is a function of only two variables, say x and v. He means to write the partial del L / del v, but *evaluated* at two different points.

[Rakeshkumar]

I keep coming to this lecture, this is such a gem.

[Euquila]

why would you say that mathematical rigor is lacking? this is a physics lecture and he is trying to convey ideas. personally, i found this lecture to be very helpful. thank you very much.