On Dec 3, 2010, at 10:04 AM, brian whatcott wrote:
The CofMass shows a ramp of acceleration which settles (finally) on f/m.
Not so. Assuming f is the net force on some well-defined object or system of objects of total mass m, then the acceleration of the center of mass is identical to f/m at all times. This is easy to show. It seems to me that Al and Jeffrey have correctly distinguished between that acceleration and the acceleration of a particle that may be at or near the center of mass. That particle's motion depends on speed of sound considerations. Not so for the motion of the center of mass.