Wheel and voltaic pile: what they have in common

1. Step 1. Wheel — is part of — Lunokhod. Wheels.
2. Step 2. Lunokhod — has part — Solar panel. A solar panel.
3. Step 3. Solar panel — is part of — Electronic calculator. Many run on a solar cell.
4. Step 4. Electronic calculator — has part — Alkaline battery. A calculator runs on a battery, sometimes on a tiny solar panel.
5. Step 5. Alkaline battery — evolved from — Dry cell. An improved zinc–manganese cell.
6. Step 6. Dry cell — evolved from — Voltaic pile. A convenient form of the galvanic cell.

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