General Relativity/Tidal forces
Radially from an object of mass m, the tidal acceleration is and perpendicular to the radial line, the acceleration is (Where G is the gravitational constant and deltaX is the seperation distance of two test particles.
To calculate those, you must remember that the acceleration due to gravity is . When you consider two test particles separated by a distance of , the results vary depending on if they are along a common radius from the center of the earth or perpendicular to it. (Any other cases can be decomposed into a combination of those two cases). Where the two test particles are radial, the two effective radii are r and (r+\Delta X). If you look at the relative acceleration between the two particles, you get
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