A force is applied to m1 connected to m2 by a "massless" cord. where m2>m1. the acceleration, a, is a = F/m1+m2 By decomposing the system into A and B where A refers to the tension on m1 upon having the force applied onto m2, the tension TA is to the positive x-direction. However, in the case of the system B, the tension TB is to the negative x-direction as the force F is applied directly to m2. Why does TB arises in the block m2 but yet not in m1?