OK, so for a small particle, [itex]\Sigma F=ma [/itex]is very straight forward. If two forces are applied to that particle, the particle accelerates, which is determined by the summation of the forces applied. But what if the object is extended one, say, a solid uniform rod (1 kg). Also, imagine that I applied 6N on the left end and 5N on the right end, perpendicular to the rod, in opposite directions. (see attached picture). What would be the resulting linear acceleration of the center of mass? Shouldn't F=ma still be applicable for center of mass only? (Obviously torque is involved in this case also, but should it affect the linear accleration of the CM?) how about an arbitrary portion of the rod (not center of mass)? Picture: The red arrow up is 6N. The blue arrow down is 5N. The grey stick is the solid rod.