David Gowers wrote:
(AFAIK there is no upward force though;
Yes, there is -- there must be, otherwise the ball would be subject to an acceleration and would move. The physical origin of this force is the electrostatic repulsion between electrons on the surface of the ball and those on the surface of the ground. The two objects come to rest just close enough together for this force to equal the force of gravity.
Every time I look at my mail I see this conversation, read the subject line rather differently than you intended, and delete it. And then someone posts another reply, so it appears again.. ._.
I've re-worded the subject to help break this cycle. :-) -- Greg