Classical Mechanics: A journey from Newton to Lagrange and Hamilton

Classical mechanics, as understood today, is largely attributed to the foundational contributions of Sir Isaac Newton, building upon the work of earlier thinkers like Galileo Galilei. Here is a brief overview of the contributions of Newton and Galileo to classical mechanics:

 

Galileo Galilei (1564-1642):

• Experimental Approach:

Galileo is often considered the father of modern physics due to his emphasis on experimental methods. He conducted a series of experiments on inclined planes and falling bodies to study the fundamental principles of motion.

•  Law of Inertia:

Galileo formulated the principle of inertia, which states that an object at rest will remain at rest, and an object in motion will continue in motion with a constant velocity unless acted upon by an external force. This laid the groundwork for Newton's first law of motion.

• Uniform Acceleration:

Galileo made significant progress in understanding uniformly accelerated motion. He developed mathematical descriptions of falling bodies, showing that the distance traveled is proportional to the square of the time elapsed.

 

Isaac Newton (1642-1727):

• Three Laws of Motion:

Newton formulated three laws of motion, which are fundamental principles of classical mechanics.

First Law (Law of Inertia): An object at rest stays at rest, and an object in motion remains in motion with a constant velocity unless acted upon by a net external force.

Second Law: The force acting on an object is equal to the mass of the object multiplied by its acceleration (F = ma).

Third Law: For every action, there is an equal and opposite reaction.

• Law of Universal Gravitation:

Newton proposed the law of universal gravitation, which states that every mass attracts every other mass in the universe with a force proportional to the product of their masses and inversely proportional to the square of the distance between their centers.

• Mathematical Formulation:

Newton's work was not only conceptual but also highly mathematical. He introduced calculus to describe motion and developed differential equations to express the relationship between force, mass, and acceleration.

• Unified Theory:

 Newton's laws of motion and the law of universal gravitation provided a unified framework for understanding a wide range of phenomena, from the motion of celestial bodies to the behavior of objects on Earth. This marked a significant departure from earlier fragmented approaches.

Together, the contributions of Galileo and Newton laid the foundation for classical mechanics, providing a systematic and mathematical framework for understanding the motion of objects and the forces acting upon them. Their work is essential for understanding the physical world and continues to be a fundamental part of the study of physics.

Development into an advanced form of mechanics

There was a lull following Newton, and it took until the end of the eighteenth century for classical mechanics to advance further. The development of classical mechanics from Newton to Lagrange and Hamilton represents a significant evolution in the understanding of physical systems. Here is a more detailed overview of this progression:

 

• Newtonian Mechanics (17th century):

Isaac Newton (1642-1727):

Newton formulated the three laws of motion and the law of universal gravitation, establishing a comprehensive framework for classical mechanics. His work laid the groundwork for understanding the motion of objects and the force interactions between them. Newtonian mechanics was basically a force-based mechanics where all motions were considered to be directly associated with forces.

• Principle of Least Action (18th century):

Pierre Louis Maupertuis (1698-1759):

    Maupertuis introduced the principle of least action, suggesting that natural processes follow paths that minimize or maximize a certain quantity called action. The principle states that "the actual path taken by a physical system between two points in its configuration space is the one for which the action, defined as the integral of the Lagrangian over time, is stationary—either a minimum, maximum or a saddle point".

• Analytical Mechanics and Euler-Lagrange Equations (18th century):

Leonhard Euler (1707-1783):

 Euler made significant contributions to mechanics, formulating the Euler-Lagrange equations. These equations provided a mathematical framework for expressing the equations of motion using the principle of least action.

• Lagrangian Mechanics (18th century):

Joseph-Louis Lagrange (1736-1813):

Lagrange further developed the analytical approach to mechanics, introducing the Lagrangian formulation. In his work "Mécanique Analytique" (1788), Lagrange employed generalized coordinates and the principle of least action to derive the equations of motion.

 

• Hamiltonian Mechanics (19th century):

William Rowan Hamilton (1805-1865):

Hamilton built upon Lagrange's work and introduced Hamiltonian mechanics. He reformulated the principle of least action in terms of the Hamiltonian function (H= Kinetic Energy + Potential Energy) leading to Hamilton's principle. In 1833, he published "On a General Method in Dynamics," which introduced the Hamiltonian formulation of mechanics. This approach uses generalized coordinates and momenta to describe the dynamics of a system, and it is equivalent to the Lagrangian formulation. Hamiltonian mechanics provides an alternative perspective, particularly useful in certain physical problems and in the context of quantum mechanics.

In summary, the development of classical mechanics from Newton to Lagrange and Hamilton involved a transition from empirical laws to more abstract and general mathematical formulations. The most striking feature of this advanced form of classical mechanics is that it is no longer a force-based mechanics like its Newtonian counterpart, but it is now based on energy. Euler, Lagrange, and Hamilton each contributed significantly to the analytical and variational approaches that are foundational to classical mechanics today. The Lagrangian and Hamiltonian formulations provide powerful tools for solving complex problems and have applications in various branches of physics.

Prabir Rudra