Why Is It So Damn Hard to Balance a Pencil on Your Fingertip?

If you've ever tried balancing something as short and skinny as a pencil on your fingertip, you know it isn't easy. Why is that? How is it possible to create a free-standing rock sculpture like this one, when it's all but impossible to balance a stinking pencil for more than a couple seconds?

Above: A balancing rock structure by the eminently talented Michael Grab. See more of his work here.

As Henry Reich explains in the latest Minute Physics, the answer to the rock-balancing question has to do with a little-known fact about the stones used in these sculptures. But the pencil? It turns out that even if you tried to balance an ideal pencil sharpened to a perfect, single-atom-wide tip, it would be all but impossible to keep it upright (in the absence of some stabilizing force). Here's why.

[ MinutePhysics]