| − | Suppose there is a potential, <math>V(x)</math>, that has a equilibrium point (minima) at <math>x_0</math>. <math>V(x)</math> can be approximated around the minima using a [[Taylor series]] as: | + | Suppose there is a potential, <math>V(x)</math>, that has an equilibrium point (minima) at <math>x_0</math>. <math>V(x)</math> can be approximated around the minima using a [[Taylor series]] as: |
| − | where <math>V'(x_0)</math>, <math>V''(x_0)</math> are the first and second derivatives of <math>V(x)</math> evaluated at <math>x_0</math>. As <math>x_0</math> is an equilibrium point, the gradient of the potential is 0 (at the equilibrium point, the net [[force]] is zero). Therefore the second term in the expansion is 0. Near to <math>x_0</math>, terms of cubic order or higher can be neglected and so the potential is approximately: | + | where <math>V'(x_0)</math>, <math>V''(x_0)</math> are the first and second derivatives of <math>V(x)</math> evaluated at <math>x_0</math>. As <math>x_0</math> is an equilibrium point, the gradient of the potential is 0 (at the equilibrium point, the net [[force]] is zero). Therefore, the second term in the expansion is 0. Near to <math>x_0</math>, terms of cubic order or higher can be neglected and so the potential is approximately: |