The physical effect on the earth curvature along a direct path between two points on the earth's surface is referred to as Earth Bulge or Earth Curve. The Earth has a radius of approximately 3965 miles. Using the Pythagorean theorem, that calculates to an average curvature of 7.98 inches per mile or approximately 8 inches in one mile. Use this online earth bulge calculator given here to find the amount of physical earth curvature bulge along a path.
Earth Bulge = 0.5 x 100000 x 100000
= 53819.4339 feet
If you are trying to figure the curvature of the earth at any distance from point a and b, this automated formula (H = 0.5 x d1 x d2) will do it for you.