Physics · Ch 1 — Nature of Physical World and Measurement
Branches of Physics
Branches of Physics
Physics is not one narrow subject but an umbrella over many branches, each opened up at a different point in history and each with its own characteristic scale, method and mathematics. Broadly, everything developed before the 20th century is grouped as Classical Physics, and everything that emerged from about 1900 onward -- when quantum ideas and relativity forced a rethink of mechanics itself -- is grouped as Modern Physics. Section 1.2.1 maps out these branches, and section 1.2.2 looks at why the subject keeps being exciting to work in, in terms of the sheer range of scales it covers and the way its discoveries happen.
Classical Physics covers the branches that were already well developed before the 20th century:
- Classical mechanics -- forces acting on bodies at rest or in motion; it further splits into statics (bodies at rest), kinematics (describing motion without asking what causes it), kinetics/dynamics (motion together with the forces that cause it).
- Thermodynamics -- the relationship between heat and other forms of energy.
- Optics -- the behaviour of light.
- Electricity and magnetism -- electric and magnetic phenomena and how the two are linked.
- Acoustics -- how sound is produced and how it propagates.
- Astrophysics -- the physics of stars, planets and other astronomical bodies.
- Relativity -- how space, time and energy are related, especially for objects moving at very different speeds.
Modern Physics covers the branches that surfaced from the beginning of the 20th century, once experiments started probing scales too small or too fast for classical mechanics to describe correctly:
- Quantum mechanics -- the discrete (quantized), rather than continuous, nature of phenomena at the atomic and sub-atomic scale; it is the broader framework, in the sense that every classical result can, in principle, be recovered from it in the appropriate limit. It further splits into a non-relativistic branch and a relativistic branch.
- Atomic physics -- the structure and properties of the atom.
- Nuclear physics -- the structure, properties and reactions of atomic nuclei. …
What this figure shows. A tree diagram with 'Physics' at the top splitting into two main limbs, Classical Mechanics and Modern; the classical side further branches into Statics, Kinematics, Kinetics and Dynamics, and separately into Thermodynamics & Kinetic Theory of Gases, Optics, Electricity & Magnetism, Acoustics, Astrophysics and Relativity; the modern side branches into Quantum Physics (splitting again into Non-relativistic and Relativistic), Atomic Physics, Nuclear Physics, Molecular Physi …
Classical Physics (recognized and developed before the 20th century):
| # | Branch | Major focus |
|---|---|---|
| 1 | Classical mechanics | The study of forces acting on bodies whether at rest or in motion |
| 2 | Thermodynamics | The study of the relationship between heat and other forms of energy |
| 3 | Optics | The study of light |
| 4 | Electricity and magnetism | The study of electricity and magnetism and their mutual relationship |
| 5 | Acoustics | The study of the production and propagation of sound waves |
| 6 | Astrophysics | The branch of physics which deals with the study of the physics of astronomical bodies |
| 7 | Relativity | Deals with the relationship between space, time and energy, particularly for objects moving in different ways |
Modern Physics (concepts that surfaced since the beginning of the 20th century):
| # | Branch | Major focus |
|---|---|---|
| 1 | Quantum mechanics* | The study of the discrete nature of phenomena at the atomic and subatomic levels |
| 2 | Atomic physics | The branch of physics which deals with the structure and properties of the atom |
| 3 | Nuclear physics | The branch of physics which deals with the structure, properties and reaction of the nuclei of atoms |