What's better, a movie clip of an internal combustion engine, or a series of stills depicting the critical phases of the combustion cycle? Evidently there is some pretty solid evidence that, at least as far as learning goes, there is little added value in watching an animation of dynamic physical processes over looking at comparable, but static graphics.
Moving illustrations may be prettier, and take up more "reel" time, but based on experimental evidence (referenced below), it seems that learners can do as well or better looking at the stills. Why?
A couple of explanations are possible. One is that the sheer speed and control of the animation may outpace the viewers ability to grasp it. Second, the moving depiction of complex processes may result in too many visual elements to observe at once. If two or more critical events occur simultaneously in the animation, the viewer may not catch them. Suppose we are looking at a cross-sectional view of a 4-cycle engine. In the time-locked presentation style of movies or television, where the learner has no control of the time-sequence, it may be difficult to see the relationship of say, the piston rods down here and the valve lifters over there on the camshaft at a given moment in time.
From a contstructivist perspective, this makes sense. Animation may be inherently more interesting at first, due to our visual brain's "orienting reflex", gaining initial attention. Understanding the action depicted however, requires independent construction, one where we perform the animation in our heads. We can do this more readily when the action is frozen and critical elements are juxtaposed and labeled properly. Putting the static pieces together allows the learner to form concepts transferrable beyond the lesson. A little of our earlier discussion of best practices for voice-over and onscreen text can help us round out this pattern.
What does the science tell us is the best practice then for demonstrating dynamic processes?
1. Offer clear visuals, the more diagrammatic the better (excluding distracting detail)
2. Offer a "structuring explanation" with VO or text (not both)
3. Offer them as stills, allowing the user to spend as much time as they need to grasp the essential parts and relations,
4. Only then do you animate the process, allowing user control over rate and direction if possible.
Ref: Cambridge Handbook of Multimedia Learning, Richard E. Mayer, ed. Cambridge University Press, p. 457