Walter H. G. Lewin, 71, a physics professor, has long had a cult following at M.I.T. And he has now emerged as an international Internet guru, thanks to the global classroom the institute created to spread knowledge through cyberspace. Professor Lewin's videotaped physics lectures, free online on the OpenCourseWare of the Massachusetts Institute of Technology, have won him devotees across the country and beyond who stuff his e-mail in-box with praise. "Through your inspiring video lectures i have managed to see just how BEAUTIFUL Physics is, both astounding and simple," a 17-year-old from India e-mailed recently. Professor Lewin delivers his lectures with the panache of Julia Child bringing French cooking to amateurs and the zany theatricality of YouTube's greatest hits. He is part of a new generation of academic stars who hold forth in cyberspace on their college Web sites and even, without charge, on iTunes U, which went up in May on Apple's iTunes Store. In his lectures at ocw.mit.edu, Professor Lewin beats a student with cat fur to demonstrate electrostatics. Wearing shorts, sandals with socks and a pith helmet - nerd safari garb - he fires a cannon loaded with a golf ball at a stuffed monkey wearing a bulletproof vest to demonstrate the trajectories of objects in free fall. He rides a fire-extinguisher-propelled tricycle across his classroom to show how a rocket lifts off. "We have here the mother of all pendulums!" he declares, hoisting [himself] on a 30-pound steel ball attached to a [rope] hanging from the ceiling. He swings across the stage, holding himself nearly horizontal as his hair blows in the breeze he created. The point: that [the] period of a pendulum is independent of the mass - the steel ball, plus one professor - hanging from it.

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