What is work?

A couple of weeks ago I had to fill out an application that asked for average number of hours worked per week. I thought the request was odd to ask of a professional. In some ways line between my hours of work and not work is fuzzy. Even when I was in college there were times I could not differentiate between working, preparation and studying. Just to make sure that I was not totally on my own in this question over Shabbat I asked a teacher how many hours a teacher works per week. He answered that it is hard to tell. Teachers need to make preparations outside of class. There is no end to the preparation and study. Even though as the years go by the preparation for any given subject may be reduced or be less intense, preparation is still part of the job. When a teacher has vacation, they continue to think and learn.

In halaha we have an exact definition of work that is forbidden on Shabbat and holidays. In physics we have a definition of work. Many kinds of work as defined in physics are allowed on Shabbat and many aspect of forbidden Shabbat work are not work in the rules of physics. If an employee keeps track of hours for the purpose of getting paid, they one can calculate the average number of weekly hours. If the amount of work never ends, then how do you answer the question of hours worked? If I grant that one can not work every hour in week, how is work defined? Is reading a book for pleasure work for a librarian? Is down time for sleep part of preparation? If your machines are working for you, are you working? If your investments are earning a return are you working? If one preparation hour can be used for two or more paid jobs, how many hours do you credit for that work? One can easily say they work more than 168 hours per week if they consider sleep as preparation and every hour their machines work is credited to more than one paid job.


So -- What is the definition of work as applicable to employment history?