1. The problem statement, all variables and given/known data I'm looking at how to calculate the tension in the ropes in an Atwood machine (two masses hanging on either side of a pulley, with mass 2 on the right side). We were told, for connected objects, that it was easiest to treat the two objects as a system and use a curved coordinate axis; then we were supposed to use this overall acceleration to find individual internal forces in a second step. 2. Relevant equations The first step is ay= (m2-m1)g/(m1+m2) But then in the second step he's suddenly giving us either of these equations to use: Fnet2y= T-m2g= m2 (-ay) Fnet1y= T-m1g=m1 (+ay) 3. The attempt at a solution ay is negative for T2 and positive for T1. Does this mean that we're no longer using the curved axis in the second step?