There are a few differences:
1. Classical mechanics deals with macroscopic objects, such as everyday objects with sizes much larger than atoms and molecules. It describes the motion of objects based on Newton's laws of motion and concepts like forces, mass, and energy. On the other hand, quantum mechanics deals with microscopic particles, such as atoms and subatomic particles, and provides a framework to understand their behavior.
2. Classical mechanics is deterministic, meaning that if you know the initial conditions of a system precisely, you can predict its future behavior with certainty using mathematical equations. Quantum mechanics, however, is inherently probabilistic. It introduces the concept of wave functions that describe the state of a system, and the outcomes of measurements are described by probabilities rather than definite predictions.
3. Quantum mechanics introduces the concept of superposition, which states that particles can exist in multiple states simultaneously. For example, an electron can be in a superposition of spin-up and spin-down states until it is measured, at which point it "collapses" into one of the states. Additionally, quantum mechanics exhibits wave-particle duality, suggesting that particles can exhibit both wave-like and particle-like behavior.