Cross-term conservation relationships for electromagnetic energy, linear momentum, and angular momentum

Cross-term conservation relationships for electromagnetic energy, linear mo mentum, and angular momentum are derived and discussed here. When two or mo re sources of electromagnetic fields are present, these relationships conne ct the cross terms that appear in the traditional expressions for the elect romagnetic (1) energy, (2) linear momentum, and (3) angular momentum, over to, respectively, (1) the sum of the rates of work, (2) the sum of the forc es, and (3) the sum of the torques, that are due to the fields of each char ge or current source acting upon the other charge and current sources. Thes e relationships, although not new, appear to be rarely recognized and used in the physics literature. As shown here, they can be extremely helpful for solving and gaining a deeper physical understanding into a rather diverse range of interesting problems in electrodynamics, including (1) aspects pf Poynting's theorem when applied to charged point particles, (2) the detaile d physical basis of electrostatic analysis, (3) understanding the connectio n between different techniques used in the past for solving Casimir force p roblems, and (4) reconciling the invalidity of Newton's third law in electr odynamics.