in today's lecture, we delve into the fascinating world of seesaws, a playground staple that offers myriad examples of basic physics principles in action. one concept often overlooked is the 'sub rosa' strategy used in design, a term borrowed from secretive practices but here meaning subtle, integral safety features that bypass direct observation. for instance, the preexpulsive mechanisms built into seesaws ensure a smoother, safer landing for younger users, a clever engineering feat not immediately apparent. when we consider redesigning or upgrading playground equipment, it's akin to deciding to restart with a clean slate, yet we always integrate those sub rosa elements to enhance safety and functionality, ensuring children's play remains both joyous and secure.