In a few chemistry books/resources I've seen the Bohr model of the atom is developed equating the electrostatic force to a centripetal force. Yet these sources also depict the centripetal force as being directed outward, away from the nucleus. (a single proton for the H atom) One even called it the centrifugal force. Another looked at centripetal force as a "separate" force, that is: (Ze^2)/(4*pi*e0*r^2) - (mv^2)/r = 0 e0 = epsilon naut The equation is correct of course, but the author stated this as an "equilibrium" condition, almost as if the net force should be 0 for a "stable orbit." Some of these derivations seem quite wrong. Isn't centripetal force a "requirement" for circular motion, in this example? If Fnet = F1 + F2 + ... Fn then centripetal force should simply be Fnet, not one of the component forces, like electrostatic attraction/repulsion, right? The centripetal force being directed outward is probably the most discomforting. Am I missing something here, or am I misinterpreting the authors? Gray's "Chemical Bonds" gives the "stable orbit" condition and directed the centripetal force outward. http://chem1.che.caltech.edu/chem1a/LectureNotes/Series01AtomsAndBohrModel.pdf [Broken] also draws the force outward and calls it centrifugal, if this helps any.