Physics that does not make use of quantum mechanics or the theory of relativity. Newtonian mechanics, thermodynamics, and Maxwell's theory of electromagnetism are all examples of classical physics. Many theories in classical physics break down when applied to extremely small objects such as atoms or to objects moving near the speed of light. ◇ Classical mechanics refers to the classical physics of bodies and forces, especially newton's laws of motion and the principles of mechanics based on them. Compare quantum mechanics.