What is Animation?

Traditional animation (Disney cartoons, Spongebob, anime and manga) is an illusion of movement.  You don't actually see things moving -- you see a series of drawings placed one after another [around 24-30 images per second] which makes your brain believe it sees movement.  That phenomenon is called Persistence of Vision.  Traditionally an artist draws/paints 24-30 drawings for every 1 second of animation.  With computers as tools, artists have the luxury of having computers complete the "in-between" frames automatically.  For example, you draw two shapes: a circle in one corner of the screen on frame 1 and then in the opposite corner around 10 seconds later -- and then you tell the computer to figure out the "in-between" (or "tween").

The nice thing about computerized "tweens" is that image one can be a tiny red circle and image 2 can be a large green square, and the computer will gradually morph them from frame to frame.

Here is a sample video:

Over 100 years ago "arcades" were full of machines that people would put coins in and look through the viewfinder as they turned a crank which would flip through a series of photographs on a big spool.  More modern examples of this technology is a "flip book".  Typically these are done by rapidly flipping through images to create the illusion of motion.

Here's a great example of using Post-It notes to create a flip book movie:

Here's an example of animation using a MUCH slower "frame rate": http://www.youtube.com/watch?v=783uWoSqdX0