In the Mechanical Engineering optional subject for UPSC, there are several topics that are more theoretical or conceptual in nature. These topics require a deep understanding of fundamental principles and concepts rather than practical application. Here are some of the specific topics that fall into this category:


- Thermodynamics is a branch of physics that deals with the relationships between heat and other forms of energy.
- It involves the study of energy transfer, work, and the properties of substances.
- Topics such as laws of thermodynamics, entropy, heat engines, and refrigeration cycles require a strong theoretical understanding.


- Fluid mechanics deals with the behavior of fluids (liquids and gases) at rest and in motion.
- Topics such as fluid properties, fluid statics, Bernoulli's equation, and fluid dynamics involve theoretical knowledge and mathematical modeling.
- Understanding concepts like viscosity, flow rate, pressure distribution, and boundary layer theory is essential.


- Solid mechanics is the branch of mechanics that studies the behavior of solid materials under external forces.
- Topics such as stress and strain, Hooke's law, elasticity, and plasticity require a theoretical understanding of material behavior.
- Concepts like axial loading, bending, torsion, and stress concentration are important to grasp.


- Theory of Machines deals with the study of mechanisms and their motion.
- Topics such as kinematics, dynamics, and mechanism design require a theoretical understanding of the principles governing the motion of machines.
- Concepts like gear trains, cams, flywheels, and balancing of rotating masses need a conceptual understanding.


- Heat and mass transfer involves the study of the movement of heat and mass from one place to another.
- Topics such as conduction, convection, and radiation require a theoretical understanding of the mechanisms of heat and mass transfer.
- Concepts like heat exchangers, heat transfer coefficients, and boundary layer theory need conceptual knowledge.


In the Mechanical Engineering optional subject for UPSC, there are several topics that are more theoretical or conceptual in nature. These topics include Thermodynamics, Fluid Mechanics, Solid Mechanics, Theory of Machines, and Heat and Mass Transfer. Understanding the fundamental principles and concepts behind these topics is essential for a comprehensive understanding of mechanical engineering.