Classical physics In contrast to classical physics, "modern physics" is a slightly looser term which may refer to just quantum physics or to 20th and 21st century physics in general. Modern physics includes quantum theory and relativity, when applicable. A physical system can be described by classical physics when it satisfies conditions such that the laws of classical physics are approximately valid. In practice, physical objects ranging from those larger than atoms and molecules, to objects in the macroscopic and astronomical realm, can be well-described (understood) with classical mechanics. Beginning at the atomic level and lower, the laws of classical physics break
Comparison of chemistry and physics studies the properties of matter at a larger scale (for example, astrochemistry) and the reactions of matter at a larger scale (for example, technical chemistry), but typically, explanations and predictions are related back to the underlying atomic structure, giving more emphasis on the methods for the identification of molecules and their mechanisms of transformation than any other science. Although both physics and chemistry are concerned with matter and its interaction with energy, the two disciplines differ in approach. In physics, it is typical to abstract from the specific type of matter, and to focus on the common properties of many