Generalized observers and velocity measurements in General Relativity

To resolve some unphysical interpretations related to velocity measurements by static observers, we discuss the use of generalized observer sets, give a prescription for defining the speed of test particles relative to those observers and show that, for any locally inertial frame, the speed of a freely falling material particle is always less than the speed of light at the Schwarzschild black hole surface.Comment: 20 pages, 1 figure, submitted to General Relativity and Gravitatio