Since a lever is a tool, its object is to assist in distributing strength or speed to the best advantage. Suppose a lever is used in moving a heavy stone. By what means can the amount of assistance rendered by it be determined? This assistance, called the mechanical advantage, is obtained by dividing the force arm or effort arm (the perpendicular distance from the fulcrum to the direction of the force), by the weight arm (the perpendicular distance between the fulcrum and the weight), or by dividing the resistance or weight by the effort or applied force. In other words, there are two ways by which a lever can be made to be of more service: first, by lengthening or increasing the force arm; second, by shortening or decreasing the weight arm.

If a mechanic, for example, desires to have more advantage, or, as he usually says, more "leverage," he may increase the length of the force arm by taking a tool with a longer handle.