Assuming there is no drag, no friction and no other objects affecting you. If you drop into the earth (through a tube). Your velocity will be 7900 m/s at the center of the earth according to http://hyperphysics.phy-astr.gsu.edu/hbase/mechanics/earthole.html
I assume that was the summation of all the velocity gained as gravitational force changes/decreases such as v= (9.8* first nano-meter traveled) + (9.7...next nano-meter traveled)+...+(0last nano-meters traveled)
I am sure there is a way to write a function using calculus (integration) that calculates your velocity at every point as you get closer. Lets approximate the earth's radius is 6,371 km and the acceleration due to gravity on the earth's surface is 9.807 m/s^2.
I will like a function that calculates your velocity at every given distance from the earth center as you fall.