If by F we mean net force on an object as calculated by measuring the objects acceleration in an inertial reference frame and dividing by m,
I say False to the first question, as there may be more than one other object causing the F on the original object, therefore -F could be partitioned amongst more than one other objects.
2nd question -- False at least in the sense described in response to first question.
JR
-----Original Message-----
From: Phys-l [mailto:phys-l-bounces@phys-l.org] On Behalf Of John Denker
Sent: Wednesday, December 11, 2013 4:01 PM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] feeler-dealer, third law, et cetera
True or false: If an object is subject to a force F, some other object must be subject to a force -F, simultaneously.
Assume short distances and long times, so we don't need to fuss over the meaning simultaneity in special relativity.
True of false: The pairing of F with -F is absolutely required by third law of motion.
Please do NOT spend more than a few minutes thinking about this. I will post my answers soon.