David Buck wrote:
> 
> Never implement undampened springs.  They will explode with small
> accumulating errors.

I posted an anim to p.b.animations many moons ago, which demonstrates this.
A falling tetrahedron behaves wonderfully until about a half second after
the rebound.  There was dampening, just not enough.

Modifying the motions equations to include third-order motion (ie, d3x/dt3)
greatly reduced the error, so that less dampening as needed.  It's
possible that calculating the dampened sinusoid which best matches the
current velocity, acceleration, and higher derivatives will yield a closer
approximation of real motion, but I haven't looked into it very far.

And since all real-world springs are very slightly dampened anyway,
a slight dampening is needful for realism.

Regards,
John

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