2nd Look...Copyright Laws

After reading several posts I realize I may have missed the mark with my first one. So here's a second go at it.

Once I had reflected on the Fair Use Copyright Laws article more closely, it seemed the law's basic intention was to find a balance between protecting the rights of authors and inventors while still allowing the use of their works to foster learning and growth.

I learned that works published over 75 years ago fall under public domain. If I am understanding this correctly, this opens up a world of texts, scripts and music that are free to use w/out infringing on the copyright laws.

In thinking about fair use and how to use copyrighted materials in classrooms there were two gray areas that surfaced. First, was the length of text that may be used. Excerpts may be used that are "short in relationship to the work". Short was not qualified other than to say a paragraph was alright, but possibly not a chapter. Percentages of a work might help to clarify matters here. Does this exist? The second, unclear topic is a bit more difficult to gauge. Under fair use, segments that do not "reflect the essence of the work" may be used. I find this very difficult to measure. Who is to judge this? Once this judgement is made...who and how does it get enforced. Seems to be an extremely daunting task.