Edublogger Copyright Rules-Start here for the answers to many of your questions.
Cornell University Copyright Chart-Copyright Term and the Pulic Domain in the United States
Copyright in the K-12 Classroom-Includes information for teachers, and Fair use guidelines, from the University of Texas at San Antonio.
Copyright Office Fast Facts- Duration of copyright.
Stanford University Fair Use Guidelines-Measuring Fair Use: The Four Factors.
Center for the study of the Public Domain-January 1, 2020 is Public Domain Day: Works from 1924 are open to all!
Copyright Crash Course- From the University of Texas Libraries.