Mechanical Engineering: The Four Major Mechanics Subjects—Thermodynamics

Today, in our series introducing the four major mechanics subjects, I would like to discuss thermodynamics.

What Is Thermodynamics?

Thermodynamics is a branch of physics that deals with heat, work, and temperature, and how they relate to energy, entropy, and the physical properties of matter and radiation.

The behavior of these quantities is governed by the four laws of thermodynamics, which provide quantitative descriptions using measurable macroscopic physical quantities. These laws can be explained in terms of microscopic constituents through statistical mechanics.

Thermodynamics applies to many subjects in science and engineering. It plays a particularly important role in physical chemistry, biochemistry, chemical engineering, and mechanical engineering, and also applies to complex fields such as meteorology.

The Laws of Thermodynamics

The four laws of thermodynamics are used to describe a thermodynamic system. These laws form an axiomatic foundation.

The first law states that energy can be transferred between physical systems in the forms of heat, work, and transfer of matter.

The second law defines the existence of a quantity called entropy. It explains the direction in which a system can evolve thermodynamically and can be used to quantify the system's state of order and the useful work that can be extracted from it.

The History of Thermodynamics

Historically, thermodynamics developed from efforts to improve the efficiency of early steam engines. In particular, the French physicist Sadi Carnot believed that engine efficiency was the key to France winning the Napoleonic Wars. The Scottish-Irish physicist Lord Kelvin first offered a concise definition of thermodynamics in 1854.

Although the early application of thermodynamics began with the study of mechanical heat engines, it soon expanded to the study of chemical compounds and reactions. Chemical thermodynamics examines the role of entropy and the nature of chemical reaction processes, contributing much of the expansion and knowledge in this field.

Other formulations of thermodynamics also emerged. Statistical thermodynamics, or statistical mechanics, concerns statistical predictions of collective particle motion based on the microscopic behavior of particles. In 1909, Constantin Carathéodory proposed a purely mathematical approach, an axiomatic formulation often called geometric thermodynamics.

This post has briefly introduced the basic concepts and history of thermodynamics. Thank you.