Sorting Twelve Instruments When Shape Misleads
At a district school music lab, the teacher unpacks twelve instruments for a practical test: two dholaks, a ghatam, a jal tarang, a morchang, three bansuris, two sitars, a tanpura, and a harmonium. Students must place each in one of four trays labelled tata, sushir, avanaddha, and ghan. A group puts the ghatam in avanaddha because it is a hollow pot, the jal tarang in tata because its bowls look like small vessels, and the morchang in sushir because it is played at the mouth. The teacher has ten minutes before the inspector arrives and wants a rule that resolves these three disputes without memorising a list. The students also ask whether the harmonium's reeds make it sushir or ghan, and whether a broken membrane automatically changes an instrument's class.
1. Assign ghatam, jal tarang, morchang and dholak to the four classes, and state the single criterion you would give the students.
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Assign by the sound-producing material, not by shape: tata = stretched strings; sushir = air column; avanaddha = stretched membrane over a resonator; ghan = solid body whose own material vibrates. Under that rule: ghatam = ghan, because the fired clay body vibrates and there is no membrane; jal tarang = ghan, because struck porcelain bowls are solid vibrators; morchang = ghan, because the metal tongue is the vibrator and the mouth only couples it to the air; dholak = avanaddha, because two stretched skins over a hollow body are the sound source. The single rule for students: ask what actually vibrates first, not whether the instrument is hollow or held at the mouth. This also explains why the ghatam's pot shape is a resonator, not a membrane.
2. A student says 'hollow means avanaddha'. Refute the claim with two examples and describe a quick listening test.
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'Hollow means avanaddha' fails on two counts: the ghatam is hollow but has no stretched skin, so it is ghan; the morchang has no membrane at all, yet it is not avanaddha. A quick listening test: strike or pluck the instrument and ask whether the pitch is controlled by a stretched skin (avanaddha), a string (tata), an air column (sushir), or a solid plate, shell or tongue (ghan). For a blindfold test, have one student play while another sorts by mechanism; then remove the blindfold and check shape. If the answer changes because of shape, the rule is being misapplied.
3. How would you classify the harmonium, and does a broken membrane change an instrument's class?
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The harmonium is sushir in the fourfold scheme: the reeds are set in motion by air from the bellows, and the air/reed system is the vibrator; it is not ghan merely because it has metal reeds. A broken membrane does not change class: a dholak with a torn skin is still avanaddha by construction, though it is temporarily unplayable. The exam-safe distinction is between the instrument's intended sound-producing mechanism and its present condition. If the teacher wants a practical test, ask students to mute the membrane and see whether the classification remains; it should.