Sunday, June 24, 2007

Newton's Principia

The Smithsonian magazine had a little blurb about the Principia in "This Month in History" for July 2007. It is the 320th anniversary of the invention of my student's favorite two classes: calculus and calc-based physics.

Made me think, gee, its seems like almost twenty years ago.

Actually, it was 20 years ago that I got a chance to read the original book.

You see, I'm so old that I remember when MTV had music videos. I remember when the "Washington meeting" of the APS, the April meeting attended by everyone except condensed matter physicists, was always held in Washington, DC. (Now it appears in more centrally-located cultural centers, such as Jacksonville, FL.) So much for being able to see a major Picasso exhibit on a lunch break. But I digress.

On a whim, I wandered over to the Library of Congress during a gap in talks I thought would be interesting. I knew that 1987 was the 300th anniversary of the book, and wondered if I could see one of the originals. It turns out that the answer was "yes". What a great experience, a connection to the origins of physics.

My most striking impression was that the pages of the book did not look that old. I have paperback books that look older. (The same was true of the Gutenberg Bible on display in the lobby.) That really made me appreciate the value of rag paper over the wood pulp we use today. We are quite correct to worry about whether digital media can be read 100 years from now, but it can't be as bad as many of our books.

Most libraries have a facsimile copy of the book (on pulp paper, so it already looks 320 years old) and/or a copy of the Cotes translation. It is worth reading to see how clearly Newton presented the main ideas of physics, and how convoluted his geometrical proofs of the calculus were. In particular, pay attention to how he invented the "vis insita" to give a name to the force Aristotle said was needed to keep things moving. His method of removing Aristotelian thinking was to define it as distinct from an "impressed force". Worth thinking about when we deal with all of those counterintuitive ideas about motion that our students bring to the classroom.

Modern textbooks take different approaches to this conceptual problem. Newton offers one that is not used much today.

PS - My understanding is that physicists don't drink enough at the hotel bar to make us desirable guests for conferences in the big Washington hotels.

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