You don't bring any noob problems to the table. You've got a problem and are asking for help here. That is exactly what this forum is meant for.

The code you show us here looks solid on a first sight. If the jerk appears about every second it is very unlikely that the error is to be found in the code you posted here. So I see basically two options in this case:

1. There is a jerk because of a sudden framerate drop. time_smooth will work against this issue, but it's not capable of miracles. You can check if this is the case by bringing up the debug panel (F11) and looking at the the framerate. If the framerate drops about every second you know that you do something very costly (in terms of cpu cycles) at a place in your code. It's even possible that your computer does something time intensice every second. However, if you can watch a framerate drop you can be sure you have a performance problem and the jerks are only symptoms of your problem.

2. You change move_vec or fall_dist somewhere else in your code but only every second. Check your code for a loop where there is a wait(-1) or a wait(64) or a simliar large value in a wait. If you manag to find such a loop the error is likely to be in this loop.