Ballistocardiography 2D: Momentum-Flux Recoil Model

A wearable doesn't need electrodes or an LED to find your pulse — it can just feel you rock. This 2D companion model drives that recoil from real momentum flux: a stroke-volume slider (mL ejected per beat) and an aortic peak-velocity slider (m/s) are combined, rocket-equation style, into an instantaneous thrust force F = v(t)·dm/dt(t), and Newton's third law flips that into the reaction pushing the body against the sensor plate. The body itself is a driven mass–spring–damper rendered as a side-view schematic — torso, spring coupling and reaction-force arrow all rise and fall with the computed displacement — while a separate strip plots the resulting accelerometer trace and runs a live beat detector on it. Heart rate, stroke volume, aortic velocity, body mass and motion noise are all live controls: watch the ejected-mass readout track the stroke-volume slider exactly, and watch the same heartbeat shrink toward the noise floor as body mass climbs, exactly as the physics predicts.