The shelf in my fridge broke, dropping my fermenter something like 10-20cm, all though he is still close, can it oxidise my beer? The wort was 2 days into the fermentation process and the yeast is safeale us-05 if that's relevant
Mostly you should be concerned with contamination. If the fall didn't compromise the lid or cause unwanted wild yeast or bacteria to get into your fermenter then you should be fine. Since I am assuming that your wort is actively fermenting then you should have a nice blanket of CO2 protecting your wort and oxidation shouldn't be an issue. I am also assuming there was not a rush of air into your fermenter through your airlock or something crazy like that. Your yeast probably got stirred up and you may have a muddy mess inside but give it a couple of days and that should settle out. So unless I am misunderstanding your situation I think you will be fine. Good luck!
If the drop did not cause your fermenter to break, and it did not cause suction of fluid through the waterlock so that air could enter, your fermentation should still be all right. I do not think that the deceleration forces would have influence on the yeast.