heard something on the radio earlier that kinda made me think, so I will pass it on for.

once again, the discussion of Mel's hole (http://www.melshole.com) came up and they were talking about what would happen if you drilled a hole all the way thru the earth to the other side. So anyways, they said something like "as you get closer to the earth's core, does the gravity increase or decrease? Does gravity originate on the crust or the core of the earth?"

I thought it was an interesting question. They didn't go into any more detail about it, but I thought about it all night. I am too tired to think about it anymore, so I thought I would post this to see what other's might think about it... or something.


if you are really bored, check that link I posted. It doesn't go into as great as detail as he says on the talk show, but still interesting.

I am fairly certain gravity increases as you get closer towards the center of the body.

The answer depends alot on the density of the earth as a function of the radius of the earth. IF the earth was a uniform density and spherical then gravity would decrease as you get closer to the center of the earth. However, the earth is definitely not a uniform denstiy and it is not a sphere. A good portion of the mass is concetrated near the center. It would not be too hard to estimate this and find out if the earth's gravity would actually increase or decrease with depth, but I cant do it now. My guess is that gravity would still decrease as you went towards the center of the earth. Maybe there is a region near the surface when gravity would increase though. I know, however, that if you were at the core, then I think the gravity would only be about a fifth of what it is at the surface.

If that concept bothers you at all, think about the very center of the earth. Since there is no preferred direction for the force, gravity must be zero there. It wouldnt make sense for gravity to jump from large to zero, so that means gravity must be smoothly decreasing in strength as you near the center.

Nate

Gravity is a manifestation of mass, so if you were at the center of the earth, mass should be distributed equally, comparing all points 180' from each other in all directions. There would be no gravity because the forces from the mass would cancel equally.

Gravity is a weak force and is not linearly proportionate relative to the distance from the mass.

Originally posted by Thutmose

If that concept bothers you at all, think about the very center of the earth. Since there is no preferred direction for the force, gravity must be zero there. It wouldnt make sense for gravity to jump from large to zero, so that means gravity must be smoothly decreasing in strength as you near the center.

Nate



so, let's say they drill that hole all the way thru the core, from here to china (or whatever :)). You try to travel thru that hole. Once you got to the center, you wouldn't be able to continue, because the gravity would keep pulling you back to the center? Kinda like you would only fall down the hole, as far as the center.

something like that?

Originally posted by Geoffrey




so, let's say they drill that hole all the way thru the core, from here to china (or whatever :)). You try to travel thru that hole. Once you got to the center, you wouldn't be able to continue, because the gravity would keep pulling you back to the center? Kinda like you would only fall down the hole, as far as the center.

something like that?

Yup!!!

ok, well, what would happen when you got to the middle? would you be ripped apart? Would the gravity force going in all directions be soooo strong, that it would just dismember you?

Originally posted by Geoffrey
ok, well, what would happen when you got to the middle? would you be ripped apart? Would the gravity force going in all directions be soooo strong, that it would just dismember you?

NOPE!!! There is a null point. I suppose you might feel it but it wouldn't tear you apart. Sort of like someone picking you up by one arm, your arm doesn't come off...

hmmmm... I will think about this more and post tom =]


very interesting.

Can't believe no one else has anything to add

Well, if you could tunnel straight thru, the gravity would increase as you came to the middle. Anything that came to the center would be pulled inward, and implode. A black hole has much more power, but same idea.

I think the null point idea is theoretically possible for a "point" object, but the ride in would be wild considering the Coriolis effect and the fact that innitially you would fly through the middle and back and forth like a yo-yo "pendulum effect" until your inertia is slowly degraded.:D

Originally posted by ChaoticThoughts
Well, if you could tunnel straight thru, the gravity would increase as you came to the middle. Anything that came to the center would be pulled inward, and implode. A black hole has much more power, but same idea.

Nope, gravity does not increase in strength as you move towards the center of the earth. The situation is actually a little different for a black hole. With a black hole, all of the matter is closer to the center than an object moving closer. With the earth, every step closer to the center you get, a large portion of the mass becomes further away from the center than you are. The result is that the force decreases to zero at the center. This does not at all mean that you do not move at the center. However, there is no net acceleration there. The result is oscillatory motion as kaj007 has suggested. Plus, there will be coriolis and centrifugal pseudoforces to worry about too, but if we only talk about gravity, then it is oscillatory.

Nate

Originally posted by kaj007
I think the null point idea is theoretically possible for a "point" object, but the ride in would be wild considering the Coriolis effect and the fact that innitially you would fly through the middle and back and forth like a yo-yo "pendulum effect" until your inertia is slowly degraded.:D


bout time

you copy and paste that? :D


j/k I am just saying that cause I don't understand a word of it!

Well, except the last part, I was kinda thinking if the gravity pulled you to the middle, but didn't stop you, you would go past the middle, then back, then back etc.... but, would your inertia ever be degraded?

Your inertia would remain unchanged, but the forces of friction would reduce your momentum until you stopped.

Originally posted by Geoffrey
ok, well, what would happen when you got to the middle? would you be ripped apart? Would the gravity force going in all directions be soooo strong, that it would just dismember you?
This is the effect where we enter the complete unknown. How does a physical body designed to operate at 1 (surface) g react when it is being pulled all directions by forces whose summation must be 1 (surface) g?

Umm, look.. an inside-out man???

Originally posted by Geoffrey
ok, well, what would happen when you got to the middle? would you be ripped apart? Would the gravity force going in all directions be soooo strong, that it would just dismember you?

Assuming that you were able to get to the center of the earth safely and also you could survive there despite all of the high pressure matter, then the forces of gravity would be rather weak and disappointing. The net sum of forces would be zero. So that leads to the question, would you get torn apart in every direction? The answer is no (always assuming a spherical earth). If you were at the center and your right arm was a little to the right of center, the mass of the earth on that side would pull your arm. However, all of the mass on the left side of the earth plus the little bit of mass between the center and your right arm would pull the other way on your right arm too. So its not like putting springs on every side of your body and pulling. Rather, it is like putting springs attached in every direction to EVERY single atom in your body. The result is that you are in a potential energy MINIMUM. This means as you step away from the center, your are attracted back, with a force proportional to how far away you are. The equations actually are exactly the same equations as a spring, meaning it is equivalent to attaching yourself to the center of the earth with a spring.

Tearing apart your body would be caused by tidal gravity forces, and I do not think that these are ever strong enough inside the earth to have an effect, since you are at a potential minimum. They mostly have an effect when you are outside of a gravitating body.

Nate

Originally posted by Thutmose


Assuming that you were able to get to the center of the earth safely and also you could survive there despite all of the high pressure matter, then the forces of gravity would be rather weak and disappointing. The net sum of forces would be zero. So that leads to the question, would you get torn apart in every direction? The answer is no (always assuming a spherical earth). If you were at the center and your right arm was a little to the right of center, the mass of the earth on that side would pull your arm. However, all of the mass on the left side of the earth plus the little bit of mass between the center and your right arm would pull the other way on your right arm too. So its not like putting springs on every side of your body and pulling. Rather, it is like putting springs attached in every direction to EVERY single atom in your body. The result is that you are in a potential energy MINIMUM. This means as you step away from the center, your are attracted back, with a force proportional to how far away you are. The equations actually are exactly the same equations as a spring, meaning it is equivalent to attaching yourself to the center of the earth with a spring.

Tearing apart your body would be caused by tidal gravity forces, and I do not think that these are ever strong enough inside the earth to have an effect, since you are at a potential minimum. They mostly have an effect when you are outside of a gravitating body.

Nate



man, you guys scientest or something? making me feel dumb :D

Originally posted by Geoffrey




man, you guys scientest or something? making me feel dumb :D

Actually, yes I am. :) Or at least about as close to a scientist as you could be without going to grad school yet.

ok I didn't take a whole lot of time to read the long posts in here.. so this could of been said..

if you were in the center of the earth you would stay there.. it would just be like gravity would be pulling you from every direction.. which is the opposite of space which is no direction..

and gravity is defined as the attractiveness of two objects..

in space even very small particles have gravity..

Originally posted by Thutmose


Actually, yes I am. :) Or at least about as close to a scientist as you could be without going to grad school yet.

Actually, you can be a scientist without going to grad school.

I'd have to agree that the further down you went in a tunnel, the less 'downward' pull you'd feel. Gravity being a manefestation of mass, as you went down toward center, the further you went, the more mass there'd be left, right, behind, etc- all pulling now too.

Of course it's hypothetical- dig a hole tha deep and you won't like what you find...kinda hot down there!