Lecture
This lecture focuses on the study of collisions, particularly the systems of two particles interacting for a brief moment. The emphasis is on using conservation laws to describe the interactions, as forces during collisions are often unknown. The lecture provides motivation by showing how conservation laws extend beyond mechanics to fields like particle physics and nonlinear optics. Examples include particle collision studies and photon entanglement production. The concept of elastic and inelastic collisions is explained, along with the dissipation of energy into heat. The lecture concludes with a detailed analysis of collisions in different scenarios, including the calculation of kinetic energy changes and the implications of different mass ratios.