This lecture covers the dynamics of mechanical systems, focusing on the example of piston machines at EPFL. It explains the space laws of the connecting rod, crank, and piston, as well as the discretization of masses and calculation of inertia forces. The instructor demonstrates how to balance oscillating forces and discusses the addition of masses to reduce oscillations. Various examples, such as piston compressors and engine crankshafts, are used to illustrate the concepts of inertia forces and mass balancing in mechanical systems.