Physical chemistry is the study of macroscopic, atomic, subatomic, and particulate phenomena in chemical systems in terms of laws and concepts of physics. It applies the principles, practices and concepts of physics such as motion, energy, force, time, thermodynamics, quantum chemistry, statistical mechanics and dynamics, equilibrium.
Physical chemistry, in contrast to chemical physics, is predominantly (but not always) a macroscopic or supra-molecular science, as the majority of the principles on which physical chemistry was founded, are concepts related to the bulk rather than on molecular/atomic structure alone. For example, chemical equilibrium, and colloids.
Sectional density is the ratio of an object's mass to its cross-sectional area. It conveys how well an object's mass is distributed (by its shape) to overcome resistance. For illustration, a needle can penetrate a target medium with less force than a coin of the same mass.
During World War II bunker-busting Röchling shells were developed by German engineer August Cönders, based on the theory of increasing sectional density to improve penetration. Röchling shells were tested in 1942 and 1943 against the Belgian Fort d'Aubin-Neufchâteau and saw very limited use during World War II.
The following outline is provided as an overview of and topical guide to physics:
Physics – natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.