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## Main Question or Discussion Point

**Why is one Tension Negative and the Other Positive -- Atwood Machines**

Hello,

Please consider the following:

I am trying to understand how to solve for acceleration when dealing with Atwood machines. I keep getting hung up on one part: the direction of tension. In the image above, why is tension in the sum of the forces for m

_{2}negative when if I were to draw a force diagram it is pointing up. Furthermore, why is gravity positive? Tension is pulling the masses up and gravity is pulling them down. A force diagram's directions are not different between m

_{1}and m

_{2}, so why are they different when summing the equations.

Many Thanks.

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