**Classical Physics and its Applicability**

Classical physics refers to the branch of physics that deals with the laws of motion and the behavior of matter and energy at macroscopic scales. It is based on Newtonian mechanics, which includes concepts like force, mass, acceleration, and motion. This branch of physics was developed before the advent of quantum mechanics and relativity theory.

**Macroscopic World**

The macroscopic world refers to the realm of objects and phenomena that are visible to the naked eye and are relatively large in size. This includes everyday objects like cars, buildings, planets, and galaxies. Classical physics is highly applicable to the macroscopic world because it accurately describes the behavior of these objects and phenomena.

1. **Newton's Laws of Motion**: Classical physics, specifically Newtonian mechanics, provides a comprehensive framework to understand the motion of objects in the macroscopic world. Newton's laws, such as the law of inertia, the relationship between force and acceleration, and the principle of action and reaction, allow us to accurately predict and explain the behavior of macroscopic objects.

2. **Conservation Laws**: Classical physics also encompasses various conservation laws, such as the conservation of energy, momentum, and angular momentum. These laws are fundamental in understanding and describing the behavior of macroscopic systems. For example, the conservation of energy allows us to analyze the energy transformations in macroscopic systems, such as the conversion of potential energy to kinetic energy in a falling object.

3. **Fluid Mechanics**: Classical fluid mechanics, a branch of classical physics, deals with the behavior of fluids (liquids and gases) in the macroscopic world. It provides tools and principles to analyze fluid flow, pressure variations, and other phenomena relevant to macroscopic systems.

**Microscopic World**

The microscopic world refers to the realm of objects and phenomena that are not visible to the naked eye and are extremely small in size. This includes atoms, molecules, subatomic particles, and quantum systems. Classical physics, based on Newtonian mechanics, is not applicable to the microscopic world.

1. **Quantum Mechanics**: Quantum mechanics is the branch of physics that describes the behavior of particles at the microscopic level. It provides a more accurate and comprehensive framework to understand the behavior of subatomic particles and quantum systems. Classical physics fails to describe the wave-particle duality, quantization of energy, and other phenomena observed at the microscopic level.

2. **Relativity Theory**: Relativity theory, both special and general relativity, deals with the behavior of matter and energy at high speeds and in the presence of strong gravitational fields. Classical physics fails to describe the relativistic effects and phenomena observed in such extreme conditions.

**Conclusion**

In conclusion, classical physics is applicable to the macroscopic world, where it accurately describes the behavior of objects and phenomena at everyday scales. However, it is not applicable to the microscopic world, where quantum mechanics and relativity theory are required to understand the behavior of particles and systems at extremely small scales and in extreme conditions.