Gravity

[Graham-W]

What would be the effect of gravity at the centre of the earth?
Would it be zero or would it tend to pull in all directions at once?

[vascop]

if something pulls in all directions equally at the same time then that's the same as zero.

[vascop]

Just to elaborate a bit, if you think of a hollow earth then inside the hollow there is no resultant gravitational force and you would be weightless.
So if you think of a point inside the hollow, then as the hollow part gets smaller and smaller the point still experiences no resultant force, and so when the point is at the centre of the sphere then again there is no resultant force.
All this assumes that the earth is a perfect sphere and that the mass density is constant for any given shell; put another way the mass density only varies with distance from the centre.

[vascop]

Of course even in non-ideal conditions (earth non-spherical etc), there would still be a point inside the earth where there would be no gravitational force.
In the ideal conditions I quoted in my last post that point would be the centre of the sphere.

[Graham-W]

I don't think if forces pull in all directions at the same time there would be zero gravity. Surely the forces would be trying to pull an object apart, like when an object approaches a black hole. If all the forces were pulling equally and were strong enough, I suspect a vacuum would be created.

[blackeyed]

gravity acts towards the center not out of it.so,in the center all the forces are acting towards the center and they effectively cancel each other out.

[blackeyed]

i dont think my first answer is scientifically correct.i apologize for that.if the forces on an object are pulling in all directions at the same time and if they balance each other the wont pull the object apart rather ,they would cancel each other and the object would feel no external force

[vascop]

Graham
You are not thinking clearly! Think again. What I have written is definitely correct.

[Graham-W]

Finally got my head round it.
If there was a shaft right through the earth and I jumped down it I would fall to the earth's centre . I may rise up a bit to the other end but would end up floating in the centre. No up or down to fall.
Thanks for all your help.

[vascop]

You got it!!! Well done!