Intermittent mechanism

This is in contrast to a continuous mechanism, whereby the film is constantly in motion and the image is held steady by optical or electronic methods.

The reason the intermittent mechanism "works" for the viewer is because of a phenomenon called persistence of vision.

The intermittent mechanism must be employed in concert with a rotating shutter which blocks light transmittance during the motion of the film and allows light through while the film is held in place usually by one or more registration pins.

In movie theater projectors, the intermittent movement is often produced by a Geneva drive (Maltese cross mechanism).

[1] The standard exposure period for regular motion in North America is 1/48 of a second, which corresponds to 180 degrees, but shutters with 200 degrees were popular back when the then-available color negative film had an ASA of 50; today's color negative film is available with an ASA of 500.

Working principle of a Maltese cross or Geneva drive
Animation of a rotating shutter . The film is transported one frame when the shutter is blocking illumination of the film.
Film advance mechanism in the Soviet Luch-2 8mm film projector, based on a Reuleaux triangle .