Aircraft carrier and headphones: what they have in common

1. Step 1. Aircraft carrier — evolved from — Ironclad. The first aircraft carriers were converted from battleships and cruisers.
2. Step 2. Ironclad — has part — Gyrocompass. Steel ships distort a magnetic compass.
3. Step 3. Gyrocompass — evolved from — Compass. A compass without a magnet.
4. Step 4. Compass — has part — Permanent magnet. The needle is a magnet.
5. Step 5. Permanent magnet — is part of — Headphones. A magnet moves the diaphragm.

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