Cognitive load has nothing to do with weights and pulley systems. 🙂
Cognition is the application of one’s mind in acquiring knowledge or understanding of a topic or idea. In a formal education context, cognitive load is the volume of learning that is expected of the student in a particular unit of time. Managing cognitive load is important as too much will push students towards surface learning and generally result in poorer outcomes.
Another aspect of cognitive load relates more specifically to multimedia learning. In this instance the learner can become overwhelmed when there is multiple channels of visual and audible stimulus provided concurrently, such as adding interesting music over to an audio/visual presentation (http://www.imej.wfu.edu/articles/2000/2/05/).