# Logical requirement of newton's third law [duplicate]

I'm describing a hypothetical universe. I'm assuming that the first law of newton holds true, that means there exists a inertial reference frame. Now the universe has three bodies.

Second law is also true for this universe.

Now if the third law is somewhat different, like $F1 = - 2F2$.

My question if i change the third law does this lead to any logical inconsistencies with the first two laws?

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## marked as duplicate by Qmechanic♦May 27 '13 at 12:00

If $F_1 = -F_2$ then $F_2 = ?$. –  Piotr Migdal Nov 7 '12 at 20:47
$F2=-2F3$ :)...i'm just saying if its different from actual third law, does not matter they differ how. –  Aftnix Nov 7 '12 at 20:51
(Ah, I should had written "If $F_1 = -2 F_2$ then $F_2=?$".) But if it is an open-ended question, then it does not fit here very well - You should only ask practical, answerable questions based on actual problems that you face. Chatty, open-ended questions diminish the usefulness of our site and push other questions off the front page. (from physics.stackexchange.com/faq) –  Piotr Migdal Nov 7 '12 at 21:59
I'm trying to understand how newton's laws are logically connected. I guess the QA should allow that. –  Aftnix Nov 8 '12 at 10:16
The point is that your proposition is not even self-consistent. So there, by logics, it contradicts everything. When it comes what should be allowed - "Does X imply Y?" is good, but "What are consequences of X?" or "I want to understand Y" are not well suited for Q&A format. –  Piotr Migdal Nov 8 '12 at 11:26