In quantum mechanics Quantum mechanics, also known as quantum
physics or quantum theory, is a branch of physics providing a
mathematical description of much of the dual particle-like and
wave-like behavior and interactions of energy and matter. It
departs from classical mechanics primarily at the atomic and
subatomic... , the particle in a box model (also known as the
infinite potential well or the infinite square well ) describes
a particle free to move in a small space surrounded by
impenetrable barriers. The model is mainly used as a
hypothetical example to illustrate the differences between
classical What "classical physics" refers to depends on the
context. When discussing special relativity, it refers to the
Newtonian physics which preceded relativity, i.e. the branches
of physics based on principles developed before the rise of
relativity and quantum mechanics... and quantum systems. In
classical systems, for example a ball trapped inside a heavy
box, the particle can move at any speed within the box a