On Fri, 28 Mar 2008 18:08:28 -0400, Adam wrote:
>Assume the mass of the Earth is 5.98 x 10^24 kg, and its radius is
>6.37 x 10^6 m.
>
>From table on same page: moment of intertia for a uniform sphere is
>2/5 m * r^2.
>
>That's too high because most of the earth's mass is at the center.
>Let's use 1/3 the actual radius to compensate.
>
>I = 2/5 * 5.98e24 kg * (1/3 * 6.37e6 m)^2 ~ 1e40 kg-m^2
Still too high:
http://scienceworld.wolfram.com/physics/MomentofInertiaEarth.html
The moment of intertia for the earth is about 8e37 kg-m^2.
So parking an extra billion metric tons of stuff 10,000 meters above
the equator would slow the rotation by about 40 microseconds per day
-- twice the limit of detection.
Changes in the wind seem to be enough to affect the rotation:
http://www.spaceref.com/news/viewpr.html?pid=10904
Earth may slow ever so slightly because of stronger winds,
increasing the length of a day by a fraction of a millisecond
(thousandth of a second).
They don't say how big that "fraction" is. The tsunami also affected
the rotation of the earth by "a fraction of a millisecond" -- but that
fraction was too small to be observable.
According to an earlier link, the threshold of detection is 0.02
millisecond.
But this link says that some kind of atmospheric influence on the rate
of rotation can be detected:
"Changes in the atmosphere ... are strong enough that their
effect is observed in the Earth's rotation signal"
And changes in the ocean show up in longer-term effects:
http://en.wikipedia.org/wiki/Chandler_wobble
On 18 July 2000, however, the Jet Propulsion Laboratory
announced that "the principal cause of the Chandler wobble is
fluctuating pressure on the bottom of the ocean, caused by
temperature and salinity changes and wind-driven changes in
the circulation of the oceans."
But where more significant issues of life are in immediate question,
this may come under the heading of "strain at a gnat, and swallow a
camel."
The discrepancy between civil and astronomical time isn't enough to
give anyone jet-lag over the course of a lifetime.
Adam
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