Ballistocardiography: Heartbeat Recoil Sensing

A wearable doesn't need electrodes or an LED to find your pulse — it can just feel you rock. Every systole ejects a slug of blood up the aorta, and Newton's third law recoils the rest of the body in the opposite direction; a chest patch, smart bed, or even a bathroom scale can pick that recoil up as a tiny periodic acceleration. This simulator drives a real second-order mass–spring–damper model with a physiologically shaped ejection-force pulse, renders the blood packets travelling up a 3D aortic arc alongside the reaction-force arrow at the chest, and plots the resulting accelerometer trace live. Heart rate, ejection force, patient body mass and motion noise are all live controls — turn up body mass and watch the same heartbeat shrink toward the noise floor exactly as the physics predicts, or crank up motion artifact and watch the beat detector below start missing and inventing beats.