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[Phys-l] oops du jour



Hi Folks --


BEWARE: The www is crawling with incorrect explanations of the
Coriolis effect. Most of the hand-wavy explanations are off by
a factor of two. (And some of them are off by a minus sign to
boot.)

I'm not just talking about student misconceptions here; Coriolis
misconceptions appear to be widespread and deep-seated even in
the physics teacher community. There was recently a big wrangle
about this on the physhare list.

The constructive part of the story is that I updated my discussion
of motion in a rotating frame
http://www.av8n.com/physics/rotating-frame.htm

I added a preliminary _qualitative_ discussion, with diagrams,
including a discussion of the oft-neglected second half of the
physics.
http://www.av8n.com/physics/rotating-frame.htm#sec-qualitative

I also cleaned up the mathematical sections of the document,
rewriting some of the key results in a more compact notation.

Suggestions for further improvements are welcome.


==============================================

While we're on the subject of misconceptions ..........

I was recently informed that
"Because water particles sit closer together than air
particles, sound travels five times faster beneath
the ocean." 41:46


This just cracks me up. It's an example of what I sometimes call
"the new type of physics" (a type unknown to physicists). I don't
know why this example strikes me as funnier then the gazillions of
other examples. (Maybe because it sounds so official and physicsy
when it talks about the particulate structure of matter and gets a
quantitative numerical result ... and because anybody who knew any
physics and thought about it for a femtosecond would know how wrong
the "explanation" is.)

I don't have anything very constructive to say about this, except
to recall that Einstein said that an education is what remains
when you've forgotten everything you learned in school. So ...
whatever happened to the principle of CHECK YOUR WORK? Doesn't
anybody learn that in school anymore?

Like the Red Queen, I've been known to believe six impossible things
before breakfast ... but I like to /check/ things before I blurt
them out in public.