Each normal mode keeps its spatial shape while oscillating at one frequency

Evidence

Note that all the beads for a given mode n share the same frequency fn, but each in general has a different amplitude an,i. The same sinusoidal function multiplies all the amplitudes for a given mode n, showing that indeed the shape is retained during the oscillation. — Eric J. Heller, Why You Hear What You Hear- An…, 791

Categorization

• DEFINE: Explains the mathematical signature of a normal mode: shared frequency, distinct amplitudes, retained shape.