Human physical intuition is based on macroscopic physical phenomena as are experienced in everyday life, which can mostly be adequately described by the Newtonian mechanics of classical physics. Early 20th-century models of atomic physics, such as the Rutherford–Bohr model, represented subatomic particles as little balls occupying well-defined spatial positions, but it was soon found that the physics needed at a subatomic scale, which became known as "quantum mechanics", implies many aspects for which the models of classical physics are inadequate. These aspects include: