make sure you edit a joint's state on every frame you apply force via the script.
this is because toribash only records your position/velocity data when you edit a joint, and the physics fill in the rest (to save filesizes on .rpl files)
it doesn't know that something happened when you apply force using the script, but when you edit a joint on the same frame, it goes "ah yes i will now write this down"
and boom u avoid those awkward teleportation moments and you can actually levitate