I saw this information about a driveshaft and how it works and thought some here might be interested. There is also a video that explains better than reading, check it out.
http://speedsociety.com/this-is-a-perfect-demonstration-on-how-your-driveshaft-works/?source=farm
http://speedsociety.com/this-is-a-perfect-demonstration-on-how-your-driveshaft-works/?source=farm