Specifically, you're looking for a simple machine that changes the magnitude or direction of a force while only requiring a single moment to operate. This description fits two of the six classic simple machines:

* Lever: A lever is a rigid bar that pivots around a fixed point called a fulcrum. It can be used to multiply force (e.g., a crowbar) or change the direction of force (e.g., a seesaw). A lever requires only one moment to operate, as it's a one-time application of force.

* Pulley: A pulley is a wheel with a groove that helps change the direction of force applied to a rope or cable. A single fixed pulley changes the direction of force, while a system of pulleys can multiply the force applied. Like a lever, a pulley operates with a single moment of force.

Important note: While the definition you provided is a good starting point, it's important to remember that the concept of "moment" can be applied to more complex machinery. Therefore, while these are the two most likely answers, there might be other devices that fit this description depending on your specific definition of "moment."