Free surface flow causes non-linearity primarily through boundary conditions, influencing flow dynamics. Thicker films exhibit greater boundary layer flow velocity, allowing surface waves to gather more fluid from thinner films, leading to breaking waves. The discussion emphasizes the mathematical aspects rather than physical explanations, prompting inquiries about specific equations involved. Reference is made to "Free-surface flow: shallow-water dynamics" by Nikolaos D. Katopodes for further insights. Understanding these dynamics is crucial for analyzing fluid behavior in various applications.
