public void ComputeForce()
{
var dist = (P2.Position - P1.Position); //e* //e* = r2 - r1
var e = dist / dist.magnitude; //e = e* / l //l = e*.magnitude
var p1V1D = Vector3.Dot(e, P1.Velocity); //p1's 1D vector //v1 = e dot v1
var p2V1D = Vector3.Dot(e, P2.Velocity); //p2's 1D vector //v2 = e dot v2
var springForceLinear = -SpringConstant * (RestLength - dist.magnitude); //fs //fs = -ks(lo - l)
var dampingForceLinear = -DampingFactor * (p1V1D - p2V1D); //fd //fd = -kd(v1 - v2)
var springDampingForce = (springForceLinear + dampingForceLinear) * e; //fsd = -ks(lo - l) -kd(v1 - v2) //times e for f1
P1.AddForce(springDampingForce); //f1 //positive value
P2.AddForce(-springDampingForce); //f2 //-f1
}