Recently, I came across a video from the 1930s explaining how a differential gear works. I think a lot of people know the purpose of the differential in our cars but have a hard time visualizing how/why it works. The first 1:50 of the video is an intro that can be skipped and from 1:50 to 3:30 motivates the need for the differential. The video after 3:30 develops the differential one step at a time. I wish I had been shown this video in my machine elements class.