1. Classical Physics: This encompasses the well-established theories that describe the behavior of matter and energy at macroscopic scales. It includes:

* Mechanics: The study of motion and its causes, including kinematics, dynamics, and statics.

* Thermodynamics: The study of heat and its relation to other forms of energy.

* Electromagnetism: The study of electric and magnetic phenomena.

* Optics: The study of light and its properties.

* Acoustics: The study of sound and its behavior.

2. Modern Physics: This encompasses the theories that emerged in the early 20th century, dealing with phenomena at atomic and subatomic scales. It includes:

* Quantum Mechanics: The study of the behavior of matter and energy at the atomic and subatomic level.

* Special Relativity: Deals with the relationship between space and time, particularly at high speeds approaching the speed of light.

* General Relativity: Describes the force of gravity as a consequence of the curvature of spacetime.

* Nuclear Physics: The study of the structure, properties, and interactions of atomic nuclei.

* Particle Physics: The study of the fundamental particles that make up matter and their interactions.

It's important to note that this division is somewhat arbitrary, as there are areas where these two branches overlap. For example, some aspects of classical mechanics are essential for understanding quantum mechanics.