This study presents an advanced extension of classical mechanics to examine photon dynamics and its parallels with cosmological phenomena, particularly dark energy. Central to this framework is the concept of effective mass (Mᵉᶠᶠ), a dynamic property uniting rest mass (Mᴍ) and apparent mass (Mᵃᵖᵖ). For photons, which have zero rest mass, their apparent mass dictates their energy-momentum exchanges and response to forces, culminating in the reformulated force equation: F = −Mᵃᵖᵖaᵉᶠᶠ. The study reinterprets Newton’s law of gravitation by integrating effective mass, allowing for ground breaking scenarios where negative apparent mass yields negative gravitational mass when −Mᵃᵖᵖ. This phenomenon echoes the behaviour of dark energy (Mᴅᴇ<0), which accelerates the universe's expansion by generating antigravitational effects.By linking photon dynamics and dark energy, this study unveils a shared mechanism: negative effective mass. This revelation provides a unifying perspective on the interplay between energy and momentum across quantum and cosmological scales, paving the way for a cohesive understanding of gravitational dynamics and fundamental forces.This nuanced exploration of photon dynamics offers significant insights for understanding the force of antigravity caused by dark energy, even when dark energy remains physically imperceptible and elusive. By extending classical mechanics to incorporate dynamic mass properties, this framework enables better mathematical modelling of the enigmatic force driving cosmic acceleration.By bridging classical and quantum mechanics with cosmological frameworks, this study deepens our understanding of gravitational interactions and lays the groundwork for future research into the universe’s fundamental workings. The cohesive interpretation of negative effective mass presented here encourages interdisciplinary exploration, with profound implications for unravelling the mysteries of dark energy and its role in shaping the cosmos.The extended classical mechanics framework thus opens pathways for new theoretical explorations, offering a cohesive mechanism to reconcile classical, quantum, and cosmological phenomena, with implications for deciphering the universe's fundamental forces.