Hi I'm having some trouble understanding spring damping, in particular, this document. Can anyone help explain where the second part of that equation comes from? I (think) understand the first part (before the + sign,) is Hooke's law, Fs=-kx (where k is spring constant and x is displacement.) With just this, the spring seems to work OK. The problem is the second part. I tried just implementing Fd = -cv for damping, then adding to Fs to get the total force, but everything went totally haywire. I took v to mean the velocity of the spring's current expansion, which is calculated using the velocities of the particles attached to the ends of the spring. So I rewrote the code as per the second part of that equation and now it works, but why? Why didn't the damping force work as calculated before? I really don't like simply taking code for granted... Clearly I am a physics noob and have done something very wrong, so be kind :)