Camshaft and sickle: what they have in common

1. Step 1. Camshaft — has part — Cam. The shaft carries several cams.
2. Step 2. Cam — is part of — Trip hammer. Cams on the shaft lift the hammer.
3. Step 3. Trip hammer — evolved from — Hammer. A trip hammer is a hammer lifted and dropped by a water wheel.
4. Step 4. Hammer — evolved from — Stone tool. The first hammer was a stone in the hand.
5. Step 5. Stone tool — evolved into — Sickle. The first sickles had flint inserts.

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