# Silly physics...

James Cozine jmcozine at yahoo.com
Wed Feb 12 14:52:25 PST 2003

```torsten at inetw.net (torsten) writes:

>>I did a lab in high school where one determines the acceleration due
>>to gravity by swinging a pendulum.  The result should have been 9.8
>>m/s^2, but we got 8.8 m/s^2.  I still don't know what we did wrong.
>>
>>-jc
>
> Where were you?  Gravity varies exponentially with distance from
> a massive body.  It is only 9.8m/s/s at sealevel.  After that, it
> decreases dramatically.

Er, given the radius of the Earth, you'd have to get pretty high up to
vary dramatically.  Given G = 6.67E-11 Nm^2/kg^2, Mass of the Earth
(Me) = 5.98E24 kg, the radius of the Earth (r) = 6.38E6 m and the
formula:

g = G (Me/r^2)

`g' is 9.7m/s^2 on top of Mt. Everest (~29,035 ft -> ~8 km).

This was Edwards, CA.  A quick search reveals the
elevation to be 2375 ft (0.7 km).

That place obviously does not follow the laws of physics.

-jc
--
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-- Walt Kelly
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