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Men Wash Your Hands!, Men Are The Secret To Longevity! Sick and Lonely Truth, What is Intelligence Anyway, Burning Water?!?, Protein Laundry, Retrovirus Revival?, Interview w/ Dr. Rolf Halden re: Environmental Toxicology.
I'm the host of this little science show. 
As to the question of the hole in the planet; If there is no air friction consideration and someone jumps into a hole through the earth they will pendulum perpetually between the two sides of the earth.
Secondly, At The center of the earth, the forces the body would feel or act upon would be inertia, the gravity force would be zero as gravity is caused by the mass of earth and the center the mass will be equally distributed around the body. If we assume that the hole is not a perfect vacuum then air friction would eventually slow down the pendulum, and after a long time the body would come to rest at the center. Alot of factors determine the velocity and length of time for this to happen; such as clothing, Air viscosity, aerodynamic characteristics of the person jumping and so many other factors. It would use a lot of computing power to figure out a formula. Also we would have to worry about heat created by the air friction. The person that jumps better have a good heat shield covering their body or they would experience the same kind of burn an astronaut would feel if they jumped from their ship while reentering the atmosphere (gee, which might be why they put heat shields on re-entering portions of spacecraft).
Sincerely,
Deepayan and Gina Acharjya
(Pronunciation guide; deep-Ion and Gina ah-charge-ya)