When you see videos of Chinese martial arts masters bouncing people back a fair distance with a very light touch (YouTube is full of them) then unless the opponent is just taking a dive (as usually found in Aikido) what you are seeing is usually an example of ‘Jin’. Jin is not unique to internal Chinese martial arts like Tai Chi Chuan – all Chinese martial arts use Jin to greater or lesser extent. Or perhaps they had it at one time, and it was lost over time. Inevitably, things get lost over time.
It’s got to the stage now that if somebody shows Jin skills then it’s assumed they have been added in as a new “internal” version of said martial art by a special master. When you see somebody who is now doing an ‘internal’ version of martial art X (Wing Chun seems a popular choice at the moment) what the master usually shows is basic Jin done with very little explanation.
So, what is basic Jin? This and other questions like it will be answered by Mike Sigman in this handy video.