Hook's Law

f=−k(x−x0)\mathbf{f}=-k\left(\mathbf{x}-\mathbf{x}_0\right)
  • ff is the force acting on a node
  • kk is the stiffness
  • x0x_0 is natural length

Force acting on particles:

f12=−k∥(x1−x2)∥(x1−x2)∥x1−x2∥f21=−f12\begin{aligned} &\mathbf{f}_{12}=-k\left\|\left(\mathbf{x}_1-\mathbf{x}_2\right)\right\| \frac{\left(\mathbf{x}_1-\mathbf{x}_2\right)}{\left\|\mathbf{x}_1-\mathbf{x}_2\right\|} \\ &\mathbf{f}_{21}=-\mathbf{f}_{12} \end{aligned}