<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">John and Vivian and others,</div><div class=""> Yes, inertial mass must be defined by F=ma and F=dp/dt as Newton defined it, though he couldn’t explain what causes it. It is caused by a particle’s circling internal momentum, as I derive in <a href="https://www.academia.edu/25641654/A_New_Derivation_of_Eo_mc_2_Explains_a_Particles_Inertia" class="">https://www.academia.edu/25641654/A_New_Derivation_of_Eo_mc_2_Explains_a_Particles_Inertia</a> , which is attached.</div><div class=""> Richard</div><div class=""><br class=""></div><div class=""></div></body></html>