Physics explains why humans can walk through crowded places and not spill their coffee – Physics World
https://physicsworld.com/physics-explain-why-humans-can-walk-through-crowded-places-and-not-spill-their-coffee/
They found that for weak oscillations, there was a sharp switch between in phase and antiphase control at the system’s resonant frequency – something that they said can be fully understood using linear systems control theory. For stronger oscillations, the duo discovered a transition region, rich in behaviour, where the motions of the cart and pendulum are not synchronized.