Thanks. I'm still a little confused by...
Which opposite forces exactly? are these the same forces that attract something outside the sphere? and why doesn't the balls position inside the sphere matter? is there some proof/formula for this?
So I'm completely lost...here's the problem.
There's a small ball inside an empty sphere. How can I prove this sphere doesn't attract the small ball gravitationally, independently of the position of the ball inside the sphere??
Also, how can I use the result from above to find the gravity...