what can be copyrighted and what can't?

I know that actual characters and story can be copyrighted. How about certain TYPES of weapons? For example, would someone be able to produce a film or write a book where the characters used some type of "plasma" or "heat" sword that are similar to a lightsabre?
If certain weapon types could be copyrighted, then I suppose there would be only one movie with laser weapons, one with "hyperdrive" etc..but these are all staples of sci-fi. I really don't know if "plasma" swords can be sued in another film or book. Does anyone have any answers?

 

The topic Legalities of lightsabers outside Star Wars discuss the lightsaber aspect and that might help you out there.

 

thank you very much for the link. It is a big help.