How to Calculate AMA & IMA of Simple Machines
The most basic reason to use machines is they provide an advantage over doing something manually. In physics, this is called a "mechanical advantage," and represents the number of times a simple machine--particularly a lever--multiplies any force applied to it. The two main types of mechanical advantage are the "ideal" mechanical advantage (IMA), or the best possible advantage a machine can offer under optimal circumstances, and the "actual" mechanical advantage (AMA), the mechanical advantage of a real machine. Calculating each of these values is simple--and the ratio of the IMA to the AMA represents the machine's efficiency.
Calculate the IMA as a ratio of the "effort distance"--the distance from the pivot point of a lever to its end, where you apply effort--to the "resistance distance," which is the distance from this fulcrum to where the machine encounters resistance, or force pushing back against its efforts. For example, if you have a lever system whose handle is 3.9 meters away from its pivot point and you begin to encounter resistance, upon pulling it, when this distance is 1.3 meters, your IMA would be 3.9/1.3, or 3.
Establish a ratio of the resistance force--the force pushing back against the lever when it encounters resistance--to the effort force--the force you apply to push it--to represent the AMA. If your textbook or physics problem notes a push to the lever system above with 11 newtons will result in a resistance force of 22 newtons, the lever's AMA will be 22/11, or 2.
Divide the lever's AMA by its IMA to calculate its efficiency. For the lever system above, the efficiency is 2/3, or .666, or 66.6 percent.