Newton’s laws of motion do not hold good for objects

Newton’s laws of motion are the foundation of classical mechanics and provide an accurate description of motion for objects at everyday speeds [1]. However, these laws have specific domains of validity and break down under extreme conditions. Specifically, Newtonian mechanics fails when an object's velocity is comparable to the velocity of light. At such relativistic speeds, space and time are no longer absolute but interwoven into a single continuum called spacetime [1]. As an object approaches the speed of light, its effective mass increases and relativistic momentum must be used instead of the classical definition. Einstein's theory of special relativity replaces Newtonian mechanics in this high-velocity regime to account for effects like time dilation and length contraction [1]. While Newton's laws remain a valid approximation for objects at rest or moving slowly, they do not hold good for relativistic motion [1].

Sources

1. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 1: The Universe, The Big Bang Theory, Galaxies & Stellar Evolution > Einstein's Theory of General Relativity > p. 5