a weird question that puzzles the mind

You can't use mgh since the object moves over a distance where gravity isn't constant. However if one were to calculate this this'd be a bitch since you can't even use your usual since the mass of the Earth is "effectively changing".

As I see it, then the air resistance would act on the object both to and from the core effectively reducing the amplitude at each oscillation, until it comes to a restful position.

Regarding the annoying part, then I guess I was a bit tired and did not formulate myself very well. What I meant to say was that I find it annoying to be wrong, and I assumed the same for you, so I did you want you to be wrong (if that makes sense..).

you could use the formula M=V2R over 2G to recalculate the mass of the earth

It would not work. the object you drop down the hole would never fall perfectly straight trough the core, since it would - according to the laws of gravity - move to the side of the hole where there is most mass. In the center of the earth, meaning the middle of the hole, there would be no mass, causing the center of gravity to move. Thus the object would probably never reach the other side.

But I guess the question is based on that the earth would be a perfect sphere so the amount of mass would be the same in all directions from the center... ;/

You know, out of all the intelligence conversation's going on here, the only thing I suddenly thought was the following: "Wait, so...if I drill to the center of the earth, does this mean I can destroy the planet?" Fraser, your a welcome addition here on Fakku, probably in the top five of people that make posts both long, relevant, and informative all in one! =)

that actually not true, there would still be gravity because gravity is always present when mass is in the equation.

yes that could be a possibility but i said "in a perfect world" meaning that the hole in the center of the world would have no negative effects to life.

You fail physics, and you fail hard. Gravity doesn't work like that.

Let's assume that the Earth has a uniform density - ergo mass - around the hole. So if we dropped the rock in the perfect center in the hole the pull on the sides would cancel out and the rock would fall perfectly straight. This can't be done, so the rock's gona be closer to one side of the tunnel than the other. It would attract it more as the force of gravity is dependent on distance. However the gravity constant is so damn small -



- that a mere couple of millimeters would cause a really miniscule force to act on the rock. So in the end if would drift probably only a couple of micrometers through its travel through Earth.

The uneven force from air drag would be several magnitudes more important, but we pumped out the air, and magic mushroom powered force fields or unobtainium walls are keeping the liquid mantle of the Earth out of the tunnel so those are not issues.

We also disregarded the fact that the Earth rotating. It means that while the rock is moving the tunnel itself around it would move. OK. We drill on the North Pole (dealing with all that ice and water will be a walk in the park compared to dealing with magma). Problem solved.

I can probably agree on that I fail at physics, since I just made a wild guess and I know nothing of gravity except that it keeps things steady. And I can honestly say that I don't understand squat of that equation.

But basically, if we follow what you say, no air resistance and the earth standing still, or we drill the hole at the exact center of the north pole etc etc, no force to interact with the movement of the rock. The rock would never come to rest right? Since the force of the rock would not be countered by any exterior force it would swing from one end of the tunnel to the other?

[size=10]Don't hate on me if I fail even more now. ._.[/h]

That is what he is saying.