Make part move with a bomb, but not by a player?

Hello. I've been concerned about something since a long time ago. Now, I noticed that I need to use that in my game. I don't know how to do it, so I'll ask here to see if somebody knows.

I've seen in many game like "Natural Disaster Survival" parts that are moved by a tornado, for example, but if a character tries to push it, the part won't move at all. How do I do that? I know to anchor parts, but if I anchor them, they won't be moved by the tornado! And I may do that when the tornado touches the parts, it sets Anchored to false, but, what if there are parts on top of it and they keep fliying even if there's nothing supporting it? I can't understand! Please somebody help on how to make a part "push-able" to determined objects/forces but not by a character and to make the part if there is nothing holding it, to fall! I can't understand! I'm seeing the matrix! PLEASE HELP!