Feynman discusses the calculation of forces in molecular systems directly, rather than through energy. This approach allows for an independent calculation of the slope of energy vs. position curves, potentially increasing accuracy or reducing labor. The force on a nucleus is shown to be the classical electrostatic force exerted by other nuclei and the electron charge distribution. The paper argues that forces are as easy to calculate as energies and that all forces on atomic nuclei can be considered classical attractions governed by Coulomb's law. The electron cloud distribution is determined by Schrödinger's equation, and nuclei are treated as fixed points. A method is presented to calculate interatomic forces without needing calculations at neighboring configurations. This method allows for the calculation of the slope of the energy curve for any configuration, reducing labor. The paper shows that two definitions of force in non-steady-state conditions are equivalent in steady-state conditions. It proves that under steady-state conditions, the force is equal to the slope of the energy curve. The force on a nucleus is shown to be the classical electrostatic attraction exerted by other nuclei and the electron charge distribution. The paper also discusses van der Waals forces, which arise from charge distributions between nuclei. The Schrödinger perturbation theory for two interacting atoms leads to the result that the charge distribution of each atom is distorted, inducing a dipole moment of order 1/R^7. The attraction of each nucleus for the distorted charge distribution of its own electrons gives the attractive 1/R^7 force. The paper concludes that intercrystalline thermal currents are the dominant cause of internal friction in annealed nonferromagnetic metals at room temperature, aside from possible macroscopic thermal currents.Feynman discusses the calculation of forces in molecular systems directly, rather than through energy. This approach allows for an independent calculation of the slope of energy vs. position curves, potentially increasing accuracy or reducing labor. The force on a nucleus is shown to be the classical electrostatic force exerted by other nuclei and the electron charge distribution. The paper argues that forces are as easy to calculate as energies and that all forces on atomic nuclei can be considered classical attractions governed by Coulomb's law. The electron cloud distribution is determined by Schrödinger's equation, and nuclei are treated as fixed points. A method is presented to calculate interatomic forces without needing calculations at neighboring configurations. This method allows for the calculation of the slope of the energy curve for any configuration, reducing labor. The paper shows that two definitions of force in non-steady-state conditions are equivalent in steady-state conditions. It proves that under steady-state conditions, the force is equal to the slope of the energy curve. The force on a nucleus is shown to be the classical electrostatic attraction exerted by other nuclei and the electron charge distribution. The paper also discusses van der Waals forces, which arise from charge distributions between nuclei. The Schrödinger perturbation theory for two interacting atoms leads to the result that the charge distribution of each atom is distorted, inducing a dipole moment of order 1/R^7. The attraction of each nucleus for the distorted charge distribution of its own electrons gives the attractive 1/R^7 force. The paper concludes that intercrystalline thermal currents are the dominant cause of internal friction in annealed nonferromagnetic metals at room temperature, aside from possible macroscopic thermal currents.