Why do music boxes play the same tune?

Answer: Metal cylinder has fixed bumps

Gears can only turn one direction — Wrong. Gears can turn in any direction. The fixed tune comes from the permanent pattern of bumps on the rotating cylinder.

Springs store only one melody — Wrong. The spring just provides power to turn the cylinder. The melody comes from the specific pattern of bumps on the cylinder.

Metal cylinder has fixed bumps ✓ — Correct! Music boxes have a metal cylinder with raised bumps arranged in a specific pattern. As it rotates, these bumps pluck tuned metal teeth (the comb) in a precise sequence, always playing the same melody. Each bump placement is permanent, creating one fixed tune.