why newton had taken force as change in momentum per time? i mean i need to get physical interpretation?what is this force actually? also help me to get an idea about energy in sense(core concept)? not with some equations? i see these equations every time?but didn't know meanining? somebody please help with these or give the name of texts which i should refer to? Calculus was invented by Newton in order to discuss the way that things vary in a concise way,ie,if it is integral calculus,it is the summation of continuous values represented by function,ie we it has a meaning;i'd like to get a simliar kinda explanation,ie,how the eqn f=dp/dt states what happens so much better than a long sentence involving instances and examples;ie,if u were the one to formulate this eqn, why would you define force like this?