Classical mechanics, which encompasses Newtonian mechanics, can explain a wide range of observations in nature within its applicable regime. It is a highly successful and accurate framework for describing the motion of macroscopic objects, such as planets, projectiles, and everyday objects. Classical mechanics provides accurate predictions for a vast number of phenomena, including the motion of objects under the influence of forces, the behavior of fluids, and the dynamics of mechanical systems.
However, there are certain observations and phenomena in nature that classical mechanics alone cannot fully explain. In the early 20th century, the field of quantum mechanics emerged to address the behavior of particles at the microscopic scale, such as atoms, electrons, and photons. Quantum mechanics introduced probabilistic descriptions and wave-particle duality, which fundamentally differ from the deterministic and continuous nature of classical mechanics.
Furthermore, at extremely high velocities or in the presence of very strong gravitational fields, classical mechanics breaks down and is superseded by Einstein's theory of relativity. Relativity provides a more accurate description of motion and gravity in these extreme conditions, accounting for phenomena such as time dilation, length contraction, and the bending of light.
Therefore, while classical mechanics is a powerful and essential tool for understanding the behavior of objects in many scenarios, it is not sufficient to explain all observations in nature. Quantum mechanics and relativity are necessary to describe phenomena at the microscopic and extreme scales, respectively. To have a comprehensive understanding of the natural world, a combination of classical mechanics, quantum mechanics, and relativity is required.