http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
https://ocw.mit.edu/courses/physics/
http://www.einstein-online.info/
https://www.physicsforums.com/
https://en.wikipedia.org/wiki/Physics
http://www.hazemsakeek.net/ar/
http://www.phys4arab.net/vb/forumdisplay.php?s=6ec8d974944eb97d9e5af042733ba8ad&f=2
http://courses-lectures.com/2016/07/learn-physics-basics/