Does anyone know which is the best definition on inertia frame of reference?
Ohanian defines "inertial reference frame" as a frame in which Newtons
laws of motion are valid to a first approximation.
Ludwig Lange argued that any three material points simultaneously
projected from a single point, and moving freely in noncoplanar
directions, constitute an inertial system.
In John Denker's website, he suggests "a freely-falling frame". (It
seems to suggest accelerated frame of reference.)
Best regards,
Alphonsus
Lange, Ueber das Beharrungsgesetz, Ber. der Ko¨nig. Sachsischen
Gesellschaft der Wissenschaften zu Leipzig, Math.-Phys. Klasse 37, 331
351 ~1885!.