The video "American Reacts Medieval Engineering | How Trebuchets Work" explains the physics behind how trebuchets were used in medieval times to launch heavy payloads including rocks, flammable materials, and animal carcasses over castle walls. Although these weapons haven't been used for over 500 years, they remain popular today for educational and recreational purposes. The video details the ratio between the long and short ends of the beam and how it affects the acceleration of the beam and the speed of the projectile. It also explains the double pendulum action that gives trebuchets their power and range, and how to accurately model their physics using iterative methods. The simulation can be used to optimize the proportions of components for maximum throwing distance. The video concludes with a promotion for NordVPN.