Gravity query

[dibble1]

If it were possible to drill a hole right through the Earth, (in one side, through the centre, and out the other side), or any other planet / object with it's own gravity, and you were to drop a ball into it. Would the ball reach a state of equilibrium in the centre of the planet or would the hole ruin the gravity field?
Thanks in advance.

[factor-fiction]

Intuitively it should reach an equilibrium but I recall that when the question was posted before there were some different answers.
Let's see what the scientists come up with on here.

[R1Geezer]

It would drop through past the centre then fall back again oscillating back and forth until coming to rest in the middle. Standard answer, to the usual question.

[fo3nix]

There's also a slight extension of this idea, to that of a gravity train.

Imagine a tunnel (at about 42 degrees if I remember correctly, for Earth), between two cities. Starting a train at once side (with no friction) will allow the train to slowly gain acceleration until half way across, when it begins to slow until it stops perfectly at the other side.

All energy is supplied from gravity, nothing else. Pretty expensive to create in the first place, though.

[dibble1]

Thanks for that and apologies if the question has been posted before, I only joined a couple of weeks ago.

[Clanad]

A pedantic addition to Mr. Geezer's offering would include the fact that the ball would weigh nothing when it came to rest at the center...

[factor-fiction]

I remember from school that acceleration due to gravity was g=9.8 m/s�. In the case of this ball being dropped down a hole to the centre of the earth does the acceleration suddenly change from 9.8 m/s� to -9.8 m/s� at the exact centre or does g change gradually?

[jake-the-peg]

The acceleration due to gravity comes from the gravitational force acting on it.

In normal situations that force is more or less constant hence a constant acceleration


In this case that force will change as the ball falls as the gravity acting on it will be counteracted by more and more mass from different locations.

[vascop]

Clanad - well that's clear, otherwise it would still be moving.

[vascop]

factor30 - that value is only at the earth's surface. It gets smaller as you move towards the centre and is theoretically zero at the centre itself.

[factor-fiction]

Thanks vascop. When I get time I'll work what speed the ball will be at when it reaches the centre and how far it will go into the southern hemisphere before fallling back.

[vascop]

That will be difficult, because the only reason it will slow down and eventually stop is because of air resistance. if you ignore any air resistance then it will keep going forever, because the energy gained in falling towards the centre will be exactly cancelled as it rises to the surface on the other side. It's an example of potential energy being converted into kinetic and back again for ever.

[vascop]

Of course I am neglecting any influence from other celestial bodies. There's just the earth and the ball you drop and the atmosphere.

[inthebegin]

nobody mentions, or maybe knows, ther Is a hole at the pole, that was discovered years ago by a pilot.he was shunned as a loony, and the airspace around it was shut down to anyone. the eath spins, like a washing macine.when ur clothes spin, they cling to the side.its the same with earth. matter clings to the side, so the core is hollow. school education is all a lie. look up hole at the pole