Hook’s Law

$\mathbf{f}=-k\left(\mathbf{x}-{\mathbf{x}}_0\right)$

• $f$ is the force acting on a node
• $k$ is the stiffness
• $x_0$ is natural length

Force acting on particles:

$$\begin{array}{rl}& {\mathbf{f}}_{12}=-k\Vert \left({\mathbf{x}}_1-{\mathbf{x}}_2\right)\Vert \frac{\left({\mathbf{x}}_1-{\mathbf{x}}_2\right)}{\Vert {\mathbf{x}}_1-{\mathbf{x}}_2\Vert }\\ & {\mathbf{f}}_{21}=-{\mathbf{f}}_{12}\end{array}$$