Journeys Through the Centre of the Earth

The title for the blog, that TJ came up with, reminded me of something I recall 'learning' in High School Physics.

I think it is somewhat common trivial-knowledge in New Zealand, that  if you drill through the center of the Earth, you would come out - half a world away - in Spain.  

For whatever reason, we were discussing this form of subterrainian transportation in our Physics class, and our teacher pretty much said it was not possible!  According to him, just as you would be ready to grab the edge of the crust in Spain, you would lose all momentum and start accelerating back toward the Earth's core once more, and there you would remain in perpetual motion.  And that is the extent of what I remember from this Physics lesson, approximately 24 or 25 years ago.

And that was also toward the end of any Physics courses I was required to do for the rest of my life.

And now I am married to a Physicist, who can probably clear the whole thing up!  

So what is the Physics?  IMPORTANT:  You will be graded on you brevity.