Now we consider a new system consisting only of m2, the 2.0-kg block. The horizontal force exerted on it by m1, the 1.0-kg block, is the external force F with arrow12 shown in the free-body diagram below. A free-body diagram of block m2. An upward arrow, originating from the top surface of the block, is labeled vector n2. A rightward arrow, acting upon the leftmost surface of the block, is labeled vector F12. A downward arrow, originating from the bottom of the block, is labeled m2 vector g. A rightward arrow, which is not connected to the block, is displayed near the upper-right corner of the block and labeled vector a. In this diagram, n with arrow2 is the normal force of the frictionless surface on m2, the 2.0-kg block. Applying Fx = max from Newton's second law to this system gives F12 = m2ax