Appeal to distorted history: Wasn't it John Paul Jones who said (according to his Chief Physicist in charge of projectile motion) "I have not yet begun to accelerate!" If you want a reference, I'll try to make one up... Jour. Sci. Nav. Warfare No. 2, page 47.
-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of John Mallinckrodt
Sent: Friday, December 03, 2010 12:11 PM
To: betwys1@sbcglobal.net; Forum for Physics Educators
Subject: Re: [Phys-l] The "why" questions
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.