Mechanical advantage force applied at "A" the end of the rope, and let "F" be the force at "B" on the moving block. Like the velocities "F" is directed downwards and "F" is directed upwards. For an ideal block and tackle system there is no friction in the pulleys and no deflection or wear in the rope, which means the power input by the applied force "F""V" must equal the power out acting on the load "F""V", that is The ratio of the output force to the input force is the mechanical advantage of an ideal gun tackle system, This analysis generalizes
The purpose of a system is what it does The purpose of a system is what it does The purpose of a system is what it does (POSIWID) is a systems thinking heuristic coined by Stafford Beer. Stafford Beer coined the term POSIWID and used it many times in public addresses. In his address to the University of Valladolid, Spain, in October 2001, he said "According to the cybernetician, the purpose of a system is what it does. This is a basic dictum. It stands for bald fact, which makes a better starting point in seeking understanding than the familiar attributions of good intention, prejudices about expectations, moral judgment,