Story → Sinusoid: Centre, Amp, Period, Start
Cosine if it starts at the top (−cosine at the bottom); sine if it starts at the centre. Reflex: Centre, amplitude, period, starting position — in that order, every time.
Cosine if it starts at the top (−cosine at the bottom); sine if it starts at the centre. Reflex: Centre, amplitude, period, starting position — in that order, every time.
6 rev/min → 10 s period. Tides: 13.6 h period. Pendulum swing 4 s ≠ height-period — height repeats every HALF swing → 2 s. "First max at 2.4" → quarter period. Reflex: Ask what quantity repeats first — that's the period, not the mechanical cycle.