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A machine is any mechanical or organic device that transmits or modifies energy to perform or assist in the performance of tasks. It normally requires an input as a trigger, and transmits the modified energy to an output, which performs the desired task.
Humans have used mechanisms and machines to amplify their abilities since before written records were available. The primary difference between simple tools and simple mechanisms or machines is a power source and a somewhat independent operation. The term machine generally applies to an assembly of parts operating together to perform work. Generally these devices decrease the intensity of an applied force, altering the direction of the force or transforming one form of motion or energy into another.
The mechanical advantage of a machine is the ratio between the resistance or load, and the force required to overcome it, although this ratio is not entirely accurate as force is required to overcome friction, as well. To compensate for this, mechanical advantage is calculated as the ratio between the distance moved by the force applied, and the distance moved by the force not applied. The mechanical efficiency of a machine is the ratio of the actual mechanical advantage (AMA) to the ideal mechanical advantage (IMA). Functioning physical machines are always less than 100% efficient.
Inefficiency of a machine is the degree or percentage to which a machine does not accomplish the work it could do without the restrictions of friction.
Modern power tools, automated machine tools, and human-operated power machinery complicate this definition greatly. Machines used to transform heat or other energy into mechanical energy are known as engines.
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