Hello everybody! I'm layman in physics, but recently I have very strong interest. Now I am struggling to obtain some knowledge all by myself. That's so complex, probably impossible for me... that's why i decided to sign up in the forum and I hope to get help from people who are versed and educated in physics. Here is the first question which I hope to get answer.... I know about the notorious formulation: p = m x v p - momentum; m - mass; v - velocity. Two weeks ago, I read a text about "free moving (circulation) in gravitational orbit". In the text they talk about orbital momentum. The formulation of orbital momentum was presented as: p = miv/(2πl) = const p - orbital momentum; m - mass; iv - orbital velocity, also: velocity of circulation (it was represented as a kind of imaginary velocity; i - imaginary unit ???) 2πl - orbital length (circumference). I searched in the physics textbooks, which I have at home... I searched in google... but i can't find information (and explanation) about this formulation. "p = m x v" is derived from "p = miv/(2πl)"? Or "p = miv/(2πl)" is derived from "p = m x v"? I will be very thankful for every comment about this mysterious formulation ( p = miv/(2πl) ).... Have a nice day everybody! P.S. English is not my native language, but I hope I managed to ask my questions clearly enough..