Answer
Analytical mechanics, the study of motion using mathematical equations, owes much to Siméon Denis Poisson. His work on elasticity, celestial mechanics, and fluid mechanics laid the groundwork for many modern theories. Poisson's equation, which describes the behavior of electrostatic and gravitational fields, is a cornerstone of physics. His contributions to Theory of elasticity, including Poisson's ratio, are still used today to understand the behavior of materials under stress.