# Strength of intermolecular forces as a function of distance

In Introduction to Mechanics by Kleppner and Kolenkow they talk about the tension force of a string and its microscopic origins. They explain how applying a force on a string slightly increases the distances between the molecules and makes them attract each other, in a way that balances the applied force. In their explanation, they present the following graph, which qualitatively describes the force between two molecules as a function of their distance.

For $$r it is repulsive, then attractive for $$r>r_0$$; moreover it reaches a maximum and then decays to $$0$$.

I'm interested in an explanation for this behavior. Which forces govern it? Why is the graph shaped as it is?

• Some aspects, such as the Van der Waals force being $1 / r^6$ for large $r$, are derived in a classic paper by Pauling. pubs.acs.org/doi/10.1021/cr60018a003 Nov 9, 2021 at 17:50