experiments in giffing

A sand pendulum that creates a beautiful pattern only by its movement.

But  why does the ellipse change shape?

The pattern gets smaller because energy is not conserved (and in fact decreases) in the system. The mass in the pendulum gets smaller and the center of mass lowers as a function of time. Easy as that, an amazing pattern arises through the laws of physics.

10

Mysterious thing, time. Powerful, and when meddled with, dangerous. Sirius Black is in the topmost cell of the dark tower. You know the laws, Miss Granger. You must not be seen, and you would do well, I feel, to return before this last chime. If not, the consequences are too ghastly to discuss. If you succeed tonight, more than one innocent life may be spared. Three turns, should do it, I think.