Harmonic spring approximation

The Harmonic spring (also known as the Hookean spring) approximation assumes that the spring obeys 'Hookes Law, i.e.

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where F is the force, x is the extension of the spring, and k is the spring constant.

This approximation is often used for chemical-bond stretching terms in various force fields:

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \Phi_{str} (r_{12}) = \frac{1}{2} K_{str} ( r_{12} - b_0 )^2 }