… for extension

# Matplotlib compatibility patch for Pyodide
import matplotlib
if not hasattr(matplotlib.RcParams, "_get"):
    matplotlib.RcParams._get = dict.get

… for extension#

The differential equation for equilibrium relations for extension is based on the infinitesimal small loaded bar:

../../_images/equilibrium1.svg

leading to :

\[{q_x} = - \frac{{{d}N}}{{{d}x}}\]

This is treated in chapter 11.1 of the book Engineering Mechanics Volume 1 (Hartsuijker and Welleman, 2006).