OK

The least important things sometimes, my dear boy, lead to the greatest discoveries.
The Doctor (William Hartnell) Serial: The Space Museum Episode: The Dimensions of Time (1965).

Gravity (Wikipedia):

Every planetary body (including the Earth) is surrounded by its own gravitational field, which exerts an attractive force on all objects. Assuming a spherically symmetrical planet, the strength of this field at any given point is proportional to the planetary body's mass and inversely proportional to the square of the distance from the center of the body.
The strength of the gravitational field is numerically equal to the acceleration of objects under its influence, and its value at the Earth's surface, denoted g, is expressed below as the standard average. According to the International Bureau of Weights and Measures, under the International System of Units (SI), the Earth's standard acceleration due to gravity is:
g = 9.80665 m/s2 (32.1740 ft/s2).
I'm beginning to have my doubts.

I know that explanation is simplistic but gravity is expected to be fairly constant on the surface of the Earth.

This week I checked out the Cosmos Mystery Area near Mount Rushmore and was astonished by one thing in particular. The pendulum.

I pushed the pendulum myself and the force required to push it to a 45o angle towards the wall from it's natural point was less than the force required to push it to a 30o angle away from the wall. The first 15o was fairly easy but the force required increased dramatically after that point.

I hate to speculate but I will. The cabin is on a hillside and there are cliffs to one side and gullies towards the other. The mountains on one side are denser than the air on the other and with much greater mass on one side it there is a greater attraction in that direction.

The pendulum naturally sets 10 to 15o off true zero. Once the pendulum is pushed passed true zero the gravitational attraction of the Earth adds to the force pulling from the mountains and makes the pendulum much harder to push.

While many of the demonstration presented in the tour may be attributed to optical illusion from the off level floors and walls or a false reference frames caused by the mountain range, I pushed the pendulum myself and the variation in force required to push it was remarkable.

I believe this and other similar areas deserve more attention than the blanket dismissals I have seen on many websites discussing the phenomena.

Update:

h/t to

h/t to LaFeminista from the Comments.

Recent analysis shows a much higher surface gravity variation.

Via Science Daily. Data from The Western Australian Centre for Geodesy.

Originally posted to Tomtech's Ramblings on Sat Aug 23, 2014 at 01:14 AM PDT.

Also republished by The KETI Program.

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