I'm confused; forgive me if this dumb. I'm trying to reason what "force" is, on a molecular level. I'm only concerned about normal forces here (pushes and pulls), not field forces. Forces in Newtons are vector quantities and only represent relationships between two things right? It isn't anything fundamental - just a way of deciding whether a mass accelerates? Let me give an example to illustrate my confusion. You pick up a twig and press it in the middle so that it snaps, and you can measure the force that surpassed the twigs shear strength that your forearms generated. Now I understand that such forces are a measurable result of molecular orbitals refusing to give way to each other, but I don't understand where the movement leading to the confrontation is coming from in the first place. In this example, you only need to go as far back as the chemical energy inside your muscle cells. Myofibers contain ATP and signalling molecules which can initiate the release of chemical energy at will. A reaction is activated where myosin heads pull along a titin molecule, and chemical energy is released from ATP afterwards. This is explained as "chemical energy being converted into movement", but I can't find any explanation more descriptive. So what's happening? Hydrolysis of ATP releases mostly heat. So is heat being absorbed by the myosin heads which then have kinetic energy, and that's the "pulling" which is then being carried down through the muscle cell so that it contracts, and the cell has tight junctions with other cells and proteins, which eventually join to tendons and bone, creating the movement of your fingers against the twig which is the "force"? So basically it's a molecular collision, where the energy comes from heat but is converted into kinetic energy, and when that kinetic energy is compromised by an obstacle, there's some conversion into force, based on mass and stiffness etc? Or does nothing on the macro scale really have kinetic energy here, and it's all more to do with angular movement/configurational change, that creates the tension between the molecular orbitals of your hands and the twig, and twisting and pivoting is ultimately being created by heat release from ATP? Many thanks.