Array ( [0] => Array ( [title] => L59A [link] => https://www.youtube.com/embed/Xc78eTzlscI ) ) 國立清華大學開放式課程OpenCourseWare(NTHU, OCW) - 第59講|Lecture 12 Electrodynamics and Relativity|12_2A 12_2 Relativistic Mechanics 12_2_1 Proper Time and Proper Velocity