Newton's Law of Motion: Surface Force Unaffected by Acceleration?

AI Thread Summary
The discussion centers on the relationship between surface forces and acceleration in Newton's laws of motion. It questions the validity of a solution that states surface forces FN1 and FN2 are unaffected by the system's acceleration, a3. The argument posits that if a3 represents the entire system's acceleration, then FN1 and FN2 should be treated as internal forces, negating their relevance in calculating a3. This raises concerns about the accuracy of the solution provided. The conversation highlights the need for clarity in applying Newton's laws to ensure correct interpretations of forces in motion.
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What I want to ask is the (b) part (It's one of our old MTs). In the solution given, it talks about an acceleration,a3, on the horizontal axis. However, in the equation, the surface forces acting on m1 and m2, FN1 and FN2, are not affected by this acceleration, a3. Isn't that wrong?
 

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If a3 is the acceleration of the whole system, then FN1 and FN2 will be internal forces for the whole system and will have their corresponding equal and opposite forces by Newton's 3rd law. Hence FN1 and FN2 must not be considered to find a3.
 

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