Actual mechanical advantage (AMA) is the force that a machine can multiply while subtracting losses from the machine having to overcome friction. Mechanical advantage (MA), on the other hand, is the factor by which a machine multiplies applied force. The mechanical advantage is calculated from the ratio of forces involved or from the ratios of the distances in which they move.
There is also ideal mechanical advantage (IMA), which is when both ratios are equal, making it easier to calculate the ratio of the distance the effort moves to the distance the resistance moves. The IMA is always more because loss for friction isn't included in the calculations. The efficiency of a machine measures how much friction and other factors reduce the overall work output from the machine. A machine that works with no friction would have an efficiency rating of 100 percent. A machine with an efficiency rating of 10 percent would only perform at one-tenth of its theoretical output.
Most machines are used to multiply a force in order to move a greater resistance, but may also be used for other purposes. With a catapult, there is a force greater than the load that moves at a short distance, causing the load to be moved a long distance before it is released. Since the load is moving farther, it has more time to build up speed before it is launched, according to The Columbia Electronic Encyclopedia.