Engineering Design Mechanisms
A mechanism may be simple or complex to achieve the desired function 
A combination of part design, assembly design and kinematics. Mechanism design acheives mechanical motion by the use of rigidly connected bodies transferring force via surface or point contact. An engine is a great example of this, it combines the mechanisms of rotary and reciprecating motion which are made more complex by the number of times their duplicated - in this case eight times and we all know the result! Mechanims are greatly used in product design (utilising gears & springs, bearings etc.) to a subtle degree or in machine design where linear, regular or irregular and intermitent motion (with time displacement) is required to achieve the desired function.