[Dave~]

There are some external factors that can not be left out that would make this experiment not work, or maybe it would make a conclusion that Gravitational Perpetual Motion is still not possible.

If we could get a hole straight through the earth, and we could keep the object continually in the center of the hole (keeping with the rotation of the earth), it would still run into the problem of colliding with air molecules, in other words, friction. The only frictionless place, hypothetically, would be inside an absolute vacuum, so that would have to be provided so that the object would not continually collide with air molecules thus slowing it down on each "orbit" (from one end of the tube to the other). Friction alone would slow it down each time so that sooner or later, the object would stop in the middle.

Of course, there is the assumption that the speed built up at one end of the tube to the middle is not sufficient enough to get the object to break the gravitational field at the other end and leave the atmosphere (slingshot effect).

Not to hijack the thread, but it's along the same lines, why can't a pump running off the natural gas and oil that it's pumping out of a pocket keep running until that pocket is devoid of all the natural gas and oil?