Hi all, I recently learned about the breakdown of Newton's 3rd law in electrodynamics and this got me thinking. The forces we consider in classical mechanics like friction and normal forces are microscopically electromagnetic interactions (repulsions?) of the atoms of two surfaces. If Newton's 3rd law doesn't hold for those interactions (which are certainly not static), how come it holds macroscopically? Perhaps it holds just as a good approximation, "on average"? Thanks in advance for any comments!