In 1961 Peter Mitchell proposed that respiration does not make ATP directly — it pumps protons across a membrane, storing energy as a proton-motive force: an electrical part (the voltage ΔΨ) plus a chemical part (the pH difference). Both push protons the same way.
ATP synthase is the turbine that cashes it in. Protons trickle back through the Fo c-ring one subunit at a time, spinning the ring and the central γ-shaft; that shaft cams the three catalytic heads of F1, and each full turn snaps out three ATP. With a ten-subunit ring, that is about 3.3 protons per ATP.
The beautiful part: it is a balance, not a ratchet. Load the shaft — push the ATP/ADP ratio up until making the next ATP costs more than the protons deliver — and the rotor stalls. Push harder and it runs backward, hydrolysing ATP to pump protons uphill. ATP synthase is a reversible motor; which way it turns is just which potential is winning. (Real rings spin ~100 turns a second; this one is slowed to watch.)
The simulation stopped unexpectedly — the lesson continues without it. You can move on; nothing you did was wrong.