I show you how spinning a saddle creates a stable well so that a ball does not roll out. This is similar to an ion trap.
STL file for saddle: https://www.thingiverse.com/thing:5188831
More info on this subject and inspiration for this video:
https://sci-hub.se/https://doi.org/10.1139/p02-110
https://sci-hub.se/https://doi.org/10.1119/1.4933206
https://sci-hub.se/https://doi.org/10.1119/1.17983
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