---- Newton's Cradle ----

This script dosn't use any calculations involving conservation of momentum, but it does show how to set and reset groups using the "tget" and "tset" methods, which store and restore the position and rotation of a group or object. This can be seen at lines 63 and 212. When making this type of rotating object, it is impossible to accurately add and subtract angles repeatedly, without introducing "zeroings errors", which show up as "misalignment" at zero degrees. "tget" and "tset" fix this by accurately storing the exact position.

The mobileStart, mobileStop, and mobileMove subroutines, are hacked from the zinc demo, and are just used for the initial "start-of-swing" of the balls. It is a rudimentary way of mouse dragging, and could use some improvements, but it is Ok for this demo.

More later.
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