Is My Physics Teacher Wrong About Teaching Force?

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The discussion centers on concerns regarding a physics teacher's methods for teaching force, with specific reference to a problem example shared by a student. Participants identify errors in the teacher's calculations, noting that while Dx and Gx were correct, Fx was not accurately determined. The application of the equation ΣF = ma is highlighted as yielding the net force rather than Fx, and the negative acceleration is questioned. Additionally, Newton's 3rd law is cited to emphasize that Gx and Fx should be equal and opposite. The student expresses intent to escalate the issue to the dean due to these instructional discrepancies.
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I believe my physics teacher to be incorrect in his methods for teaching force. I drew up a quick example of the type of problem we're covering, and I'd like to know whether you believe the statements to be true or false.

[PLAIN]http://img263.imageshack.us/img263/9185/forcesproblem.jpg
 
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godvilla said:
I believe my physics teacher to be incorrect in his methods for teaching force. I drew up a quick example of the type of problem we're covering, and I'd like to know whether you believe the statements to be true or false.
Looks like some basic errors were made:
Dx was found correctly.
Gx was found correctly.
Fx was not found correctly.

Applying ΣF = ma to box 2 gives the net force, not Fx. And why was the acceleration made negative?

Newton's 3rd law will tell you that Gx and Fx must be equal and opposite.

(I'm making the assumption that no other forces are involved. The blocks are sliding along a frictionless surface, for example.)
 
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Exactly! That was my point too. Sounds like I'll be going to see the dean.
 

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