Over three centuries after Isaac Newton formulated the laws of motion and universal gravitation, this paper demonstrates that additional fundamental implications of Newton’s concept of inertia remain to be explored. By re-examining inertia and its intrinsic relation to energy, gravity, motion and heat, a unified physical framework is proposed. Matter is shown to express its natural inertia through two fundamental, intrinsic forces: inertia-at-rest (Ir), a pulling force driven by sharing-energy (Es), and inertia-in-motion (Im), a pushing force driven by excess-energy (Ee). Under this framework, gravity (F) and weight (W) are recognised as direct expressions of inertia- at-rest (W = F = Ir), which draws particles together to form hierarchical, nested structures termed unities ─ ranging from base particle groups and atoms to planets, stars, and galaxies. Conversely, when acted upon by a sufficient external pushing force (Im ≥ Ir), a unity member is displaced into a free particle. Heat is redefined as the pushing force (Im) of free particles, and radiation is generalised as heat transfer through successive particle collisions until Ee is dissipated and the particle rejoins a unity. Applying these principles provides new perspectives on several core physical concepts: conventional quantum models are re-evaluated, electric generators are recognised as electric transferors, and electromagnetic phenomena, including the motor effect, are unified under electronism ─ where magnetic fields are shown to be electronic fields of circling free electrons. Because matter organises and moves relative to its respective unity centre, reference frames and relativistic dependencies are nullified. Ultimately, the universe is shown to evolve through repeated cycles of unity formation, heat transfer via free particles, and reintegration, offering a cohesive, ground-up foundation for physics built directly upon Newtonian principles.