Question

Why is a single fixed pulley used as its mechanical advantage always less than 1?

Answer 1

A single fixed pulley only changes the direction of the effort; it does not multiply the force. For an ideal, frictionless pulley, its mechanical advantage is exactly 1. In a practical pulley, some effort is used to overcome friction and the resistance of the pulley, so the useful load lifted is less than the effort applied. Thus, the actual mechanical advantage is less than 1.