Okay, class... here’s what a proficient answer sounds like. Different objects make different sounds because they vibrate at different frequencies — size, shape and material change the vibration. Those different frequencies can be compared, and when we choose notes with certain frequency relationships we create musical harmony. A ratio describes the relationship between two quantities. In music a ratio describes the relationship between two frequencies. A 2:1 ratio is called an octave — the higher note vibrates twice as fast as the lower. One early thinker who studied these ideas was Pythagoras. He used a monochord, a simple single‑string instrument with a moveable bridge, to test how changing string length changed pitch. Think of the monochord as a ruler for sound: one string stretched over a soundboard, marked lengths, pluck and listen. It helps you measure frequency relationships and hear ratios as musical intervals. For success, answer clearly: identify vibration and frequency, define ratio, link ratio to frequency, name the octave for 2:1, and describe the monochord as a single‑string measuring tool. This links maths and music — ACARA v9: proportional reasoning meets The Arts. Nice work — sing the numbers. Keep curious. Practice listening. Bring questions tomorrow and share discoveries.