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Welcome to the Khan Academy
January 31, 2009 9:38 AM   Subscribe

Sal Khan likes explaining things, and he's really good at it. Here he is on CNN giving an excellent explanation of the financial crisis. And here's a great explanation of Newton's Law of Gravitation. His YouTube channel has over 700 lectures and you leave understanding everything he talks about no matter the subject.
posted by y10k (21 comments total) 64 users marked this as a favorite

you leave understanding everything he talks about no matter the subject.

Pshaw! That's just like me when I'm drunk! I assume
posted by Navelgazer at 9:59 AM on January 31, 2009

Wow, the KAAAAAAAHN Academy website is pretty comprehensive. I don't really know much about KAAAAAAAHN, apart from seeing him here and there on CNN, but I like that there are people this passionate about knowledge. Yep, I look forward to seeing more of KAAAAAAAHN in the future.
posted by Marisa Stole the Precious Thing at 10:01 AM on January 31, 2009 [3 favorites]

thanks! these are great, like if cecil adams or marilyn savant had a youtube channel/classroom for the world :P

fwiw, i thought this was a great one paragraph description from menzie chinn james hamilton about why, in a nutsehll, all these (synthetic) CDOs were created in the first place:
I believe there was an unfortunate interaction between financial innovations and lack of regulatory oversight, which allowed the construction of new financial instruments with essentially any risk-reward profile desired and the ability to leverage one's way into an arbitrarily large position in such an instrument. The underlying instrument of choice was a security with a high probability of doing slightly better than the market and a small probability of a big loss. For example, a subprime loan extended in 2005 would earn the lender a higher yield in the event that house prices continued to rise, but perform quite badly when the housing market turned down. By taking a leveraged position in such assets, the slightly higher yield became an enormously higher yield, and while the game was on, the short-term performance looked wonderful. If the agent is compensated on the basis of current performance alone, and the principal lacks good information on the exact nature of the risks, the result is a tragically toxic incentive structure.
and a little more in depth: micro and macro crisis explainers from satyajit das (while brad setser makes the connection)... oh! and for extra credit check out george soros' recent missive :P
posted by kliuless at 10:22 AM on January 31, 2009 [1 favorite]

This is just fantastic. I needed to brush up on my math for the GRE and for some future stats classes, and the Khanucopia looks ideal. Thanks for posting this.
posted by GrammarMoses at 10:30 AM on January 31, 2009

Oh for crying out…two of them are called "dice," but when you have one all alone, it is a "die." Do you people buy "a mice" at the pet store, or use "a knives" to cut up your food?
posted by paisley henosis at 10:36 AM on January 31, 2009

posted by Navelgazer at 10:37 AM on January 31, 2009

Wow, the KAAAAAAAHN Academy website is pretty comprehensive. I don't really know much about KAAAAAAAHN, apart from seeing him here and there on CNN, but I like that there are people this passionate about knowledge. Yep, I look forward to seeing more of KAAAAAAAHN in the future.

Unless you're Madeline, the H is before the A.
posted by George_Spiggott at 11:22 AM on January 31, 2009

Yeah, but the damage was done. Ah well.
posted by Marisa Stole the Precious Thing at 11:32 AM on January 31, 2009

Huh. I had that same "new bank" Idea. To bad it will never happen since Wall Street owns D.C.
posted by delmoi at 12:47 PM on January 31, 2009

Wow, an amazing learning math resource. Generous to have it all up on YouTube, nicely organized. Thanks.
posted by nickyskye at 2:22 PM on January 31, 2009

Dude! This is awesome. Goddamn if I could just have the smarts contained in the tip of his pinky finger. Thank you for the post.
posted by Jeremy at 3:51 PM on January 31, 2009

Fantastic! Thank you!
posted by grumblebee at 4:46 PM on January 31, 2009

WARNING! I found a mistake in the first math video I looked at, volumes of solids of revolution. He drew the line x = -2 but called it y = -2. A simple mistake you may say, but EXACTLY the kind of mistake students might make and really something that should have been fixed or edited out.
posted by wittgenstein at 5:21 PM on January 31, 2009

I watched the first episode on calculus and was somewhat unimpressed. I really can't fault the author for his sincere effort at educating a lay audience on such a fundamental topic, for expending time and effort to help others, asking nothing in return; however, I have some very strong reservations about the style of these lessons. (Granted, I stopped after the first video, so I will admit that maybe the collection shows some brilliance as a whole, but I really doubt this...)

My problem with the popular approach to mathematics education is that lessons like these seem to be little more than an audio track to a textbook. For example, the author here starts his first lesson on calculus with derivatives, a discussion of slopes and graphs, and how to apply limits to calculate the slope of a tangent line as a function of a secant line with rapidly approaching end-points. Yet throughout this, there's never any motivation or meaning provided. (What is a derivative, where is this going, and why does it all even matter?)

I really don't think these are irrelevant, touchy-feely questions. To the contrary, I think that they are the most important questions to the student. While mechanical definitions are undeniably a necessary component of any understanding of the topic, I can't see how, robbed of context, they would be of any actual use to anyone but a robot performing arbitrary mathematical manipulations day in and day out. Of course, this happens to describe the typical high school student, whose mathematical education is geared around ultimately meaningless, mechanical work that human-built, automated tools (like Mathematica) will always do cheaper, more accurately, and with greater efficiency. (This isn't, though, a criticism of rote exercise as a means of cementing knowledge but a criticism of rote exercise as an end in itself.)

I don't mean to hold it against this particular author for generously providing an educational resource on such an important topic. It's just that I think this style of education lets the teacher, who is supposed to be wiser, more experienced, more knowledgeable, do all the easy work (- the mechanical explication of terminology,) and leaves the student, who is inexperienced, is lost, and knows nothing, to actually figure out how it all fits together and what it all means.

As a lifelong student and an occasional teacher, I find it very frustrating.
posted by Sangermaine at 5:52 PM on January 31, 2009 [3 favorites]

While mechanical definitions are undeniably a necessary component of any understanding of the topic...

I learned calculus in physics class more than math class, I think. When I read "mechanical definitions", I immediately thought of rockets and pendulums.
posted by ryanrs at 12:04 AM on February 1, 2009

Coming to this as someone who dropped out of Pre-Calc in college, I actually found his calculus lessons pretty easy to understand, but then again, I already knew what Calculus is for, having read up on Newton, etc.

I think you could consider these more tutorial lessons, assuming you're also taking the class, though.
posted by empath at 10:12 AM on February 1, 2009 [1 favorite]

Sangermaine, I can sympathize with that. I've come to love this guy's explanations, although I admittedly haven't looked through the entire site yet, his stuff on logs and calculus were illuminating for both myself and a friend. I'm retaking a few things after years of not using it and I never even really realized that I never learned what half of this stuff was for. Knowing there is a point to something definitely helps up the motivation to learn it.
posted by six-or-six-thirty at 11:27 AM on February 1, 2009

Erm... In that Newton's Law of Gravitation video he says that the Universal Constant of Gravitation isn't a constant, and that it can change. Which is nonsense. I think he's confused because it can't be measured very accurately.
posted by alby at 2:42 AM on February 2, 2009

You'd think that, if you are going to make 700 videos of yourself explaining things, you'd learn how to record sound.

And agreed about the pedagogy. Some people are definitely going to understand the "audio textbook" version...but there is no lack of that format whatsoever. As others have noted, I learned the mechanics of calculus in math class but I didn't understand it until physics. And I didn't really feel comfortable using it until I applied it to the "real world" (by which I mean math puzzles, but at least it wasn't all set up for me in the text).
posted by DU at 6:03 PM on February 2, 2009

ALBY, special relativity tells us that the gravitational constant actually does vary depending on the velocities (and therefore) masses of the objects. It also does seem to change with scale and time:


L M Stephenson
Department of Electrical Engineering, University College London

Abstract. It is shown that an assumed annual cyclical variation of the gravitational constant is sufficient to eliminate the systematic errors which have been noted in the last two redeterminations of the gravitational constant. Such a variation is consistent with a previously proposed theory, is not in contradiction with the latest experimental measurements of the acceleration due to gravity, or with the null Eotvos result, and is thus consistent with the weak equivalence principle.
posted by paman at 12:57 PM on February 5, 2009

paman, that's from an article entitled "A possible annual variation of the gravitational constant" from 1967 that's only ever been cited once. That's your best reference?
posted by alby at 12:15 PM on February 7, 2009

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