Lecture 3 | Modern Physics: Classical Mechanics (Stanford)

[H4zarD1337]

720p pls :D

[jellyfish501]

Tnx Stanford ofr this videos. I really enjoy seeing and hearing this.

Susskind really gives a best view of the basic principles in physics, and science

And puts down the basic assamptions on the table as should be

Thank u mister really inspiring and helpfull

[awsomenesscaleb]

Did that guy seriously just get offended because the professor called curved coordinates screwball? WTF.

[potpie921]

Amazing vid!

[grunder20]

Physics deals in everyday life. From the moment you wake up, until the time you go to bed. Great video!

[Tikorous]

The guys in this class are just painful, I'd have bitch slapped them if I was him.

[agapitoflores001]

This is awesome. Great discussion by the physics prof.

[SalsaTiger83]

I like the attitude, normally integration by parts would be considered part of the "most basic mathematical foundations obvious to the most casual observer"

[klgamit]

a little mistake in the equation he writes from 1:31:00 i think, m r double dot is not minus partial U to r because it's actually partial L to r and L depends on r not only through U but also through the kinetic term of the angle.... (it's the centrifugal term)

[sloochy]

I have maxed the volume of my PC and headphones as much as I can, and I can still barely hear this :(

[ripperduck]

These lectures are FAR better than any physics lecture I ever had at U of O

[kmav81]

integral A(t)f(t) = 0 only implies A = 0 if A is continuous?

[PLecN]

@kmav81 It's just a maths technicality. It's true because you can find discontinuos functions A(t) where int A(t) f(t) = 0 but A(t) is not 0 everywhere. Eg A(t) = -1 on [-1,0] and A(t)=+1 on [0,1]. So A discontinuous on [-1,1]. Can choose f(t) to be anything ... f(t)=1 is easiest. Now int A(t)f(t) = 0 over interval [-1,1] but A(t) is not zero.

[fuckshitass911]

@PLecN

nice try. but wrong approach.

integral of A(t)f(t)=0 implies the function A(t)f(t) is identically zero.

since f is arbitary, it follows A(t) should be zero, as f can be chosen to be 1.

[PLecN]

@fuckshitass911 (great moniker) Thanks. Yes forgot must make int A(t)f(t) = 0 for *all* f, not just a particular one. Was trying to find discontinuous A where int A(t) f(t) = 0 for arbitrary f(t), but A(t) not zero everywhere. What about worst case scenario, A(t) = 1 if t is rational, zero otherwise?

[fuckshitass911]

@PLecN

A(t) must be continuous.

otherwise for any A(t) that is almost 0 everywhere also satisfies the property.

[fuckshitass911]

@fuckshitass911

and the derviative of the integral will not be defined at some points, if A(t)f(t) is not continuous.

[PLecN]

@fuckshitass911 Why would the derivative of the integral be relevant in this particular case? You wouldn't need it for the proof of the theorem. Just wondering.

[NoTryOnlyDo]

Excellent lectures, really helping me with my Calculus of Variations Module... Thankyou Stanford and Leonard Susskind!

[Liaomiao]

I can follow the maths as i just learned calc 1-3 in my spare time, but the physical concepts are just a little too difficult for me. I feel that I only need to know a tiny bit more to understand all this fully, but right now it feels somewhat scattered. I'm still very glad these lectures are put up for all to view though. Thanks Stanford and Susskind.

[TheOvermaster]

holy fuck that guy needs to shut up - DAMN

[superok4luv2u]

isn't this hamilton principal not principal of least action

[ibreakkidslegs]

@superok4luv2u same thing

[jreedmcu1]

I am privileged to be able to access this an my discretion, thank you Stanford! but i do have a hard time hearing. 

[jreedmcu1]

I am privileged to be able to access this an my discretion, thank you Stanford!

[paulojunior201]

man this level of physics is beyond real, i don't understand anything :S

[loonyTunes86]

Thanks for allowing me to access these lectures.

[stangmonkey1]

Thank you Stanford!

[ibreakkidslegs]

classical mechanics for retards

[TheOvermaster]

@ibreakkidslegs he explains it slowly - but this is in no way basic classical mechanics...

[ibreakkidslegs]

@TheOvermaster hahaha yes that's that I meant. Classical mechanics for retards who already know the stuff up to Lagrangian formalism

[rks4sm]

THIS has rekindled my interest in physics!I couldn't have imagined otherwise after leaving college so many years ago..thanks stanford!

[QuantumMaths]

Simply having a short discussion on the generalized chain rule for partial derivatives would have saved me considerable time lol :P

[QuaternionEM]

Summary:

Derivation of the Principle of Least Action and the

Euler-Lagrange eq.

Derivation of Newtons laws from the PLA.

Several examples using the Lagrangian to derive

conservation laws and the associated symmetries.

Awesome.

[Zovk]

Whoever recorded this should be publicly flogged because i can't hear it. NEEDS TO BE LOUDER!!!

[wideeyedraven15]

Or you should be flogged for being so safely rude in the anonymity of the Internet. Troll. This kind of presentation, given for free, is gold. The sound could be louder but I can hear it. Your ingratitude and lack of manners is disgusting.

[Zovk]

What's it to you? If you're appreciative of something than you notice ways to in improve, make them known so it can be improved. Discourse and criticism leads to progress but you're a regressive creature. Stagnant human shit. I did not attack the lecture i attacked the damn volume and whomever the idiot is by which the videos potential was limited by their ineptness. Unless you're them mind your own business you fucking cunt.

[ArabicPilot]

@Zovk turn the volume up dumbass

[fielsjd]

I feel so privileged to have access to these lectures. Thanks, Stanford.

[XanglesPrime]

@fielsjd All education should be free.

[yes1123]

At 1:31:05, he says that dL/dr = -dU/dr. Why is the 1/2*m*r^2*theta-dot^2 term not taken into account?

Shouldn't dL/dr = -dU/dr + m*r*theta-dot^2?

[MyAce81]

@yes1123 He doesn't say that. First of all, they are two separate equations he writes down on separate lines (the lower equation is the time derivative of the upper one). Second, the reason that the term you mention doesn't come into account is that the derivative is with respect to r-dot (not r, look close), and the second term of L does not explicitly depend on r-dot.

[yes1123]

@MyAce81 I was referring to the right side of the second equation. At that point, he is applying the Euler-Lagrange equation: d(dL/dr-dot) / dt = dL/dr. I agree that the left-hand-side is mr-doubledot, but the partial on the right-hand-side (dL/dr) is with respect to r, not r-dot.

[MyAce81]

@yes1123 Ah, yes, sorry, you are correct. Or at least i see the problem now. That term would correspond to some "pseudo-force" i guess? The centrifugal force maybe?

[marsCubed]

I loved uni, I could happily sit through physicslectures all day to nourish my mind. Thanks Stanford.

[coolie13]

around 17 and 20 minutes, didnt he talk about that stuff in the last lecture

[exfalsoquodlibet]

0:12:54

That's not true.

A(t) could for example be the function, which is 1 at 0 and 0 everywhere else and it would have the property.

[kotalik4]

It's true under the condition that A(t) is well-behaved; in particular, it should be continuous

[pedrofonini]

I think what matters is that the integral of A(t)dt is zero

[rmnbrw]

well f(t) is ANY function, so it can be infinit at 0, as for example delta function and have integral of 1 with your defined A(t)

[exfalsoquodlibet]

The lebesgue integral of this would still be 0.

The lebesgue integral of any function which is zero everywhere but on a set of measure zero is zero.

[doublebitaxe]

@rmnbrw Technically the "Dirac delta function" is not a function, though it can often be thought of as a function. In this case I don't think the dirac delta should be considered; however any arbitrarily tall and skinny spike would be ok. In this context, the "blip function" needs to have some width.

[ikanrajah]

The sound repro sux! some lectures are loud enough this one's so soft! dont Stanford check its otuputs for quality? coming from an ivy league, this sux!

[jmc8197]

He doesn't emphasise that the Euler-Lagrange equations are fundamental to classical mechanics because they can be derived from the Principle of Virtual Work and Newton's second law. Since the Euler-Lagrange equations can also be derived form the Principle of Least Action, then the Principle of Least Action is just another reformulation of classical mechanics, and not a postulate of physics.

[jonnylazer]

is that telling Lenny about physics...tut tut

[jmc8197]

reminding him that he's lecturing to undergrads

[FoolHarvey]

...this is not an undergraduate class...the people in this class have paid money to be in the company of an emminent physicist. I think the lectures are great...I have a degree in electrical engineering though...whats your background ?

[jmc8197]

I have a degree in electronic engineering, but take an interest in physics as a hobby.

[Frostalzzz]

heh, exactly the same here. I got my engineering degree last year(after 5 long hard years) and I felt that some courses(obviously tailored to engineering studies) weren't giving us the complete picture. Most stuff we saw on quantum mechanics, langrangian, Hamiltonian, ...

were giving on a fairly superficial basis and always left me with some questions.

Now I'm following a master in Physics in my spare time while working as an analog design engineer.

[FarFromEquilibrium]

why is lecture 2 private??

[janfrinta]

where is lecture 2?