This lecture covers the principles of gear systems, focusing on straight gears and their load-bearing capacities. It begins with the analysis of bending resistance and practical tensile strength, providing formulas for calculating the minimum module required to withstand specific loads. The instructor presents numerical examples, illustrating how to determine gear dimensions based on applied forces and material properties. The discussion includes the importance of selecting appropriate gear modules and widths to ensure durability under operational stresses. The lecture also addresses the design considerations for helical gears and bevel gears, emphasizing their advantages in terms of noise reduction and efficiency. Additionally, the instructor explains the mechanics of gear trains, including epicyclic gear systems, and their applications in automotive differentials. The session concludes with a practical demonstration of gear manufacturing processes, highlighting the significance of precision in gear design and the impact of material selection on performance.