redbird: closeup of me drinking tea, in a friend's kitchen (Default)
posted by [personal profile] redbird at 11:58am on 2007-03-14
"Or even everywhere on earth."

Not only does the stuff I'm currently copyediting do a lot of explanations of newtons and the like, several of the books (it's a series, each state gets slightly different content, because they each have different standards and tests, plus some of the examples are tailored locally: Pennsylvania gets examples about its rivers, Louisiana about a train to New Orleans, etc.) have, as an example of reading data off a line graph, the acceleration of gravity at different latitudes.
 
posted by [identity profile] mishamish.livejournal.com at 02:14pm on 2007-03-14
Uhm... seriously? How much of a difference IS there between latitudes?
redbird: closeup of me drinking tea, in a friend's kitchen (Default)
posted by [personal profile] redbird at 01:20am on 2007-03-15
Not enough that you'd notice casually, but enough to be easily measurable. The polar radius of the Earth is about 20 miles greater than the equatorial diameter (since g=Gm1m2/d2, reducing d increases g), and centrifugal force reduces felt gravity, again moreso at the equator and diminishing toward the poles.

A google on "gravity latitude" produces, among other things, links to calculators to let you take this into account when reading a barometer, and the information that the definition of g (i.e. Earth's gravity) specifies sea level at 45° latitude.
 
posted by [identity profile] redaxe.livejournal.com at 02:24pm on 2007-03-14
If you're interested in the topic (and not just editing it), you may want to read the letter to Physics Today I mention below, in which a man experimentally verifies time dilation via altitude (he spent two days up Mount Rainier with his family, having installed cesium clocks both at home and in the minivan).

Links

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