Leonardo begins dissecting human cadavers, a practice forbidden by the Church at the time. His detailed anatomical drawings revolutionized the understanding of human anatomy and physiology. These studies were driven by his desire to understand the physical basis of human movement and expression for his art.

Employed by Ludovico Sforza, Leonardo designs innovative weapons, fortifications, and siege machines. His inventions include early prototypes of tanks, armored vehicles, and various artillery systems. These designs often incorporated advanced mechanical principles.

Leonardo develops numerous designs for flying machines, including ornithopters (machines that flap their wings like birds) and gliders. He meticulously studies bird flight and attempts to replicate its principles in his inventions. While none of his flying machines were successfully built during his lifetime, they demonstrate his visionary thinking.

Leonardo designs canals, irrigation systems, and hydraulic pumps to improve water management. He studies the flow of water and develops innovative solutions for diverting and controlling water resources. His projects included plans for canals around Milan.

Leonardo creates detailed anatomical drawings of the human body, showcasing his understanding of muscles, bones, and organs. His "Vitruvian Man" (c. 1490) exemplifies his exploration of human proportions and their relationship to geometry and the universe.

Leonardo studies geological formations, fossils, and the Earth's history. He theorizes about the formation of mountains and valleys and observes the effects of erosion and sedimentation. His geological observations were remarkably prescient for his time.

Leonardo's curiosity extended to optics. He studied light and shadow, the working of the human eye, and perspective, applying his insights to improve his painting techniques and understand the natural world. His investigations included experimenting with lenses and mirrors.