Friday, March 16, 2012

Khan’s Video Lectures on Acceleration and Newton’s Second Law

Stimulated by “Re: Khan Academy on Sixty Minutes” [Hake (2012)], I went into the Khan Academy and looked at two videos:

1. “Acceleration” at, and

2. “Newton's Second Law” at

These consist of Khan’s blackboard solutions of algorithmic exercises to find:

(1) the acceleration “a” of a Porsche, given the change in its velocity “v” during a change in time “t”; and

(2) the acceleration “a” of a block, given its mass “m” and the force “F” acting on the block.

There’s little attempt to lead students to a conceptual understanding of either acceleration or Newton's Second Law. There’s no emphasis on operational definitions of “velocity,” “time,” “acceleration,” “force,” or “mass.”

Khan appears to be (a) oblivious of physics education research, and (b) simply repeating in a traditional way the cookbook stuff he learned at MIT in passive-student lectures.

I note that there’s a 68-post thread “Khan Academy: Math instruction goes viral” on the MathEdCC at which contains, among other things, negative comments on Khan’s math video on averages at

For example:

a. Guy Brandenburg (2011) wrote: “That is one of the worst lessons on stats and averages I have ever seen. . . . He acts like the important part is the computation itself. He gives no reason WHY we should add the numbers up then divide. . . . . . And people pay him money? And think he's doing a great job?. . . . He's about as bad as John Saxon.”

b. Domenico Rosa (2011) wrote: “I have not seen many of Khan’s videos, and his style of teaching is significantly inferior to the teachers that I had in the public school system in the factory city of Everett, MA. My point is this: All the hits that his videos are getting are indicative of the hunger for direct instruction -- a fact that has been completely missed by the media pundits who have been giving him so much exposure.”

Richard Hake, Emeritus Professor of Physics, Indiana University
Honorary Member, Curmudgeon Lodge of Deventer, The Netherlands
President, PEdants for Definitive Academic References
which Recognize the Invention of the Internet (PEDARRII)
Links to Articles:
Links to SDI Labs:

“I point to the following unwelcome truth: much as we might dislike the implications, research is showing that didactic exposition of abstract ideas and lines of reasoning (however engaging and lucid we might try to make them) to passive listeners yields pathetically thin results in learning and understanding - except in the very small percentage of students who are specially gifted in the field.”
Arnold Arons in Teaching Introductory Physics (p. vii, 1997)

REFERENCES [URL’s shortened by and accessed on 16 March 2012.]
Arons, A.B. 1997. Teaching Introductory Physics. Wiley, publisher's information at information at Note the searchable “Look Inside” feature.

Brandenburg, G. 2012. “Re: Khan Academy: Math instruction goes viral,” on the OPEN! MathEdCC archives at Post of 7 Sep 11:01 PM to MathEdCC. (The Math Forum fails to specify the time zone.)

Hake, R.R. 2012. “Re: Khan Academy on Sixty Minutes” on the OPEN! AERA-L archives at Post of 15 Mar 2012 10:59:14-0700 to AERA-L and Net-Gold. The abstract and link to the complete post are being transmitted to several discussion lists and are also on my blog “Hake’sEdStuff”" at with a provision for comments. I apologize for the several misspellings of "Khan" as "Kahn." It was all the fault of my spiel chequer - see e.g., Zar (1994, 2000).

Rosa, D. 2011. “Re: Khan Academy: Math instruction goes viral,” on the OPEN! MathEdCC archives at Post of 12 Sep 1:59 PM to MathEdCC. (The Math Forum fails to specify the time zone.)

Zar, J. 1994. “Candidate for a Pullet Surprise,” Journal of Irreproducible Results, January/February, p. 13. Reprinted “by popular demand” in the Journal of Irreproducible Results 45(5/6), 2000, p. 20; online at

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