Sadly, the follow-up "Betty Boop explains Uncertainty" never made it past the initial sketches

OK, just kidding about Betty, but the incredibly inventive Fleischer Studios did produce this interesting attempt at introducing Einstein to the masses (if you'll pardon the expression).

From Wikipedia;

Six months later, on February 11, 1923, the Fleischers released their relativity film, produced in collaboration with popular science journalist Garrett P. Serviss to accompany his book on the same topic. Two versions of the Fleischer film are reported to exist - a shorter two-reel (20 minute) edit intended for general theater audiences, and a longer five-reel (50 minute) version intended for educational use.[1] 

The Fleischers lifted footage from the German predecessor, Die Grundlagen der Einsteinschen Relativitäts-Theorie,[2] directed by Hanns-Walter Kornblum, for inclusion into their film. Presented here are images from the Fleischer film and German film. If actual footage was not recycled into The Einstein Theory of Relativity, these images and text from the Scientific American article suggest that original visual elements from the German film were.[3] 

This film, like much of the Fleischer's work, has fallen into the public domain. Unlike Fleischer Studio's Superman or Betty Boop cartoons, The Einstein Theory of Relativity has very few existing prints and is available in 16mm from only a few specialized film preservation organizations.