Sail and vacuum pump: what they have in common

1. Step 1. Sail — is part of — Windmill. A windmill’s sails are cloths on rotating arms.
2. Step 2. Windmill — evolved into — Wind turbine. A windmill with a generator instead of millstones.
3. Step 3. Wind turbine — has part — Electric generator. A generator.
4. Step 4. Electric generator — has part — Stator. The stationary part with the windings.
5. Step 5. Stator — is part of — Vacuum pump. A cylindrical chamber.

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