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Re: [Phys-l] 9.80 vs. 9.81

Some cool pictures of the nonuniformity in the earth's gravity can be
found at
http://www.csr.utexas.edu/grace/gallery/animations/ggm01/index.html
http://www.csr.utexas.edu/grace/gallery/gravity/ggm01_asia.html
or in general
http://www.csr.utexas.edu/grace/gallery/gravity/

Also: the technique used to obtain this data is a nice example of
modern experimental physics. You can mention it to students as an
example of what physicists do for a living.

The data is valuable to companies that are prospecting for oil and
minerals. You can mention this as an example of why geologists
need to know some physics.

The US Navy has verrry detailed gravitational maps of the world's
oceans. Submarines use the info for navigation. (Other navigation
systems -- such as GPS and LORAN -- don't work underwater.)



On 04/20/2008 06:24 AM, Michael Edmiston wrote in part:
.... they first seem surprised it is not 9.81. Then they
discover they don't have a clue how to go about finding it (other than
Google, which does not lead them to the USGS number for our location).

Googling is an acquired skill. Sometimes it is necessary to
take several stabs at it, improving the query each time. It
took me about a minute to conjure up the following gem:
http://irpsrvgis00.utep.edu/repositorywebsite/


It is reasonably easy to use (although clicking on the map
doesn't do anything, alas). It can produce magnetic data as
well as gravity data, such as:

Gravity Dataset - Total Records: 12
SourceCode LatNAD27 LatNAD83 LonNAD27 LonNAD83 Elevngvd29m Elevngvd88m ObsGrvLess976000mg ITC OTC FAAnom CBAnom267
--------------------------------------------------------------------------------------------------------------------------------------------------
6415_113 40.8698350 40.8698872 -083.9378360 -083.9377779 0259.60 0259.45 4122.37 00.06 00.01 -044.19 -073.54
6415_111 40.8773350 40.8773874 -083.9189990 -083.9189402 0253.80 0253.65 4123.03 00.05 00.00 -045.99 -074.70
6415_90 40.8779980 40.8780507 -083.8618320 -083.8617709 0258.70 0258.55 4119.83 00.02 00.01 -047.74 -077.02
6415_110 40.8786660 40.8787183 -083.9355010 -083.9354428 0252.00 0251.85 4125.24 00.03 -00.01 -044.45 -072.99
6415_98 40.9063340 40.9063864 -083.9373320 -083.9372739 0245.90 0245.75 4128.29 00.00 -00.01 -045.76 -073.64
6415_89 40.9080010 40.9080538 -083.8613360 -083.8612750 0253.20 0253.06 4122.42 00.04 00.00 -049.53 -078.18
6415_97 40.9098320 40.9098846 -083.8993300 -083.8992704 0247.10 0246.95 4125.36 00.01 -00.01 -048.63 -076.64
6415_231 40.9275020 40.9275548 -083.8805010 -083.8804407 0245.30 0245.15 4125.51 00.00 -00.02 -050.62 -078.44
6415_99 40.9346660 40.9347184 -083.9355010 -083.9354428 0240.40 0240.25 4131.65 00.04 -00.02 -046.63 -073.86
6415_100 40.9348340 40.9348867 -083.8994980 -083.8994384 0243.80 0243.65 4128.75 00.00 -00.01 -048.50 -076.14
6415_88 40.9363330 40.9363859 -083.8620000 -083.8619390 0242.60 0242.45 4126.07 00.00 -00.02 -051.69 -079.20
6415_230 40.9384990 40.9385518 -083.8805010 -083.8804407 0245.90 0245.75 4126.33 00.00 -00.01 -050.60 -078.48

There may be better data available from other sources, but this
is still pretty impressive.

Hint about the relevance of that data:
http://maps.google.com/maps?spn=0.03,0.03&ll=40.9098846,-83.8992704&q=40.9098846+n+83.8992704+w