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Re: [Phys-L] feeler-dealer, third law, et cetera



Say a block sits on a frictionless table. Joe pushes it to the right with
a 20 N force. Mary pushes left with 5 N. Thus the block "is subject to"
F=15 N. I can't find an object "subject to" -15 N.
On Dec 11, 2013 5:39 PM, "Rauber, Joel" <Joel.Rauber@sdstate.edu> wrote:

I'll bite.

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.

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