Bell gong and gyroscope: what they have in common

1. Step 1. Bell gong — is part of — School bell. A metal cup resonator.
2. Step 2. School bell — has part — Electromagnet. An electromagnet strikes the hammer.
3. Step 3. Electromagnet — works like — Permanent magnet. An electromagnet attracts iron like a permanent magnet, but only while current flows.
4. Step 4. Permanent magnet — is part of — Compass. The needle is a magnet.
5. Step 5. Compass — evolved into — Gyrocompass. A compass without a magnet.
6. Step 6. Gyrocompass — has part — Gyroscope. A gyroscope.

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