Newton's law of motion cannot be applicable to the particles moving at a speed comparable to the speed of

Newton's laws of motion are the foundation of classical mechanics, which accurately describes the motion of macroscopic objects at speeds much lower than the speed of light (v << c). However, these laws are no longer applicable when particles move at speeds comparable to the speed of light (approximately 3 × 10⁸ m/s).

At such high velocities, the effects of Albert Einstein's Special Theory of Relativity must be considered. In relativistic mechanics, mass is not constant but increases with velocity, and space and time are interconnected. Speeds of sound, rockets, and bullet trains are extremely small compared to the speed of light, meaning Newtonian physics still provides a highly accurate approximation for them. For subatomic particles in accelerators moving near c, classical equations yield incorrect results.