‘Faculty’ is the word used to refer to the entire teaching staff.
Examples: The faculty agreed to work on a Sunday.* Our faculty will be on strike all of next week.
The word `faculties’ is used to refer to the power of the mind or body. In other words, you are talking about an individual’s physical and mental abilities.
Examples: The man is nearly 95 years old. You can’t possibly expect him to be in possession of all of his faculties. * The man was drunk. He definitely wasn’t in control of his faculties.