Andrew Coppin wrote:
> 
> [...]
> 
> But... suppose the object is contrained to the X-Y plane. (And let's suppose
> that whatever mechanism "constrains" it has no friction - impossible but
> simpler to compute ;-) What do we do now? Do we just write V = <5, -7, 0>
> and continue as usual? Or does something more ellaborate need to be done?

There are mainly two possibilities to achieve this:

1) use coordinates that completely and uniquely describe the motion of the
object and at the same time do not violate the constraints.  In this case
it would mean calculating the whole thing in 2d in the x-y-plane.

2) introducing additional forces to make the object fit the constraints
(commonly known as penalty methods) This is quite easy, also for
complicated constraints but if you want the objects to fit the constraints
very precisely the integration of the equations of movement will be quite
difficult (small stepsize required).

Christoph

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