This lecture covers the fundamental concepts of constraints, power, work, and kinetic energy in mechanics. It begins with the analysis of a vertical metronome, detailing the forces acting on it, including weight, normal reaction, and elastic forces. The instructor explains the motion laws governing the metronome's behavior, emphasizing the conditions for equilibrium and small oscillations. The discussion then transitions to the concept of a circular rail, where the angle of detachment of a mass is determined based on its velocity. The lecture utilizes the kinetic energy theorem and the conditions for detachment, illustrating the relationship between forces and motion. Finally, the lecture introduces a conical pendulum, analyzing the forces acting on it and deriving the equations of motion. Throughout the lecture, the instructor provides clear examples and mathematical formulations to illustrate the principles of mechanics, making the content accessible and engaging for students.