hi people ive been a member for ages but neva really posted much just liked reading the stuff u put on here but i have a question for everyone......
if u dig a hole all the way to the other side of the earth get rid of the molten core then dropped an object into the hole,when the object reaches the centre would it stay there and just keep goin back and forth in stead of goin to the otherside i started thinkin bout this when me and my mate were just talkin about mindless things and this happened to pop up we argued for ages and then asked my mum and she said no it would go all the way through the hole but then i thought about the gravity on the other side of the planet would it just cause it to stay lol i aint to smart so if all u guys could answer this it would help settle this argument thx oh and i didnt know were to post this so i put it here if its in the wrong place could someone please try and move it to the right area thanks

You are correct, the object would stop when it reached the centre of the earth.

All of the matter in the earth is exerting a gravitational pull on the object you drop. When the object reaches the centre the earth will be pulling equally on it from all directions, hence it will stay stationary.

Gravitational attraction decreases with distance from the earth's (or any other body's) center. Hence you would weigh fractionally less than normal at the top of Everest and fractionally more than normal at the bottom of a very deep well.

Good question, waspie dwarf just about covered it i think.

Hmmm... Yeah, things fall because of gravity, but, by the time something reaches the center of the earth, wouldn't its velocity & momentum keep carrying it further beyond the center?

I mean, you can throw a ball upward and gravity does not prevent it. I think you would have to measure the velocity of the object vs. the strength of gravity to find out how far the object would travel past the center of gravity. It would be different based on the object's mass as well.

I've been thinking along these lines and I suspect that you are right, it's momentum would initially carry it beyond the centre. It would then fall back towards the centre again. It may do this several times but it would eventually come to rest at the centre of the planet.

Once in the middle, are the forces pulling or pushing on the object, would it be torn apart or compressed?

Using the Newtonian model of gravity then gravity always pulls so it will be pulled equally in all directions. However that applies because we have this hypothetical shaft down which our object has fallen. In our model the centre of the earth is esentially hollow.

In reality the center of the earth isnt hollow and so its centre is under compression. This is because ever piece of matter in the planet is attracting every other piece of the matter in the planet. It is as if it is all trying to find its way to the centre. This puts the core under tremendous pressure (this is the reason why, despite the high temperatures at the centre of the earth, there is a solid core).

I'm not sure I understand.

Say we were able to magically produce a sphere of some unmeltable alloy smack dab in the center of the earth.

What forces are acting on it and in which direction? From the center, all mass is outward, so it should pull outward, no? Also, being in the center, all mass is gravitating toward it's opposite end of the earth, pulling inward, no?

You have it right, there are seemingly contradictary forces at work here, but really it is all just gravity. The mass of the earth is trying to pull our object in all directions simultaneously. It remains stationary because the forces all cancel each other out.

But as well as this the earth itself is trying to contract. It is attempting to become a singularity like in a black hole. All of the earths mass is trying to fall towards the centre. But gravity is not strong enough to make an object the earth's mass and diameter collapse. Still the whole earth is pushing towards the centre causing pressure.

yay finnally an answer thx u guys i might start posting more on here and finnally my mum was wrong hahaha in your face mum

Always respect your Mum, remember the 2 rules:

1. Your Mum is always right.
   
2. When your Mum is wrong see rule 1.

^Lmao.

Well, I'll have to have a debate with my science teacher, he thinks that if there was a tunnel going from one side of the Earth to the other through the core, if an object fell through it it's momentum would force it past the centre and it would keep going from one side to the other for any given amount of time.

Pfft...public education.

I think he is right to a degee, there probably would be a period of osscillation but it would eventually die away leaving the object stationary.