Bjoern Schliessmann wrote:
> Gabriel Genellina wrote:
>
>
>>For what I can
>>remember of my first love (Physics): if you have a small ball
>>moving inside a spherical cup, it would be almost crazy to use
>>cartesian orthogonal coordinates and Newton's laws to solve it -
>>the "obvious" way would be to use spherical coordinates and the
>>Lagrangian formulation (or at least I hope so
Having actually solved that problem in simulation, I can report
that it's easier in Cartesian coordinates. I used to use this as
a test of Falling Bodies, one of the first physics engines that
really worked on the hard cases.
Spherical coordinates seem attractive until you have to deal
with friction between the ball and cup. The ball is rotating, too,
and may be slipping with respect to the cup. Then the simple
Physics 101 approach isn't so simple any more.
John Nagle
Animats
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