There is a very interesting feature of the human eye actually allows animation to exist.
It is in fact a flaw in our eyes that is known as persistence of vision; first written
about by Peter Roget in his paper The Persistence of Vision with Regard to Moving
When an object is placed in our line of sight and then rapidly taken away, we actually
see the object there for a fraction of a second longer then it is really there. If
that first object were taken away and then replaced by a second object, the persistence
of vision would actually blend the two images together to make a smooth transition.
Imagine if we didn't have that flaw in our eye and we did in fact see every movement of
an animation. When the first cel were taken away and quickly replaced with the next
we would see a moment where there was no picture at all [the moment when the pictures were
being switched]. This would give all animation a very jerky look to them, and it wouldn't
look like the characters on screen were moving naturally at all.
Images illustrait this point int the other sections.
The speed at which this
fusion frequency occurs is usually around 40 Hertz (Hz) or 40 frames per second.
Classical animation is usually shown at 24 frames per second, but has a rotating blade that
interrupts a single frame 2 times in order to have a rate of 48 Hz or 48 frames per second.