Rifling and petri dish: what they have in common

1. Step 1. Rifling — uses — Angular momentum. Spin stabilizes the bullet.
2. Step 2. Angular momentum — is used in — Potter’s wheel. A heavy disc keeps spinning by inertia.
3. Step 3. Potter’s wheel — is used in — Pottery. The wheel made shaping vessels faster and more even.
4. Step 4. Pottery — evolved into — Saucepan. The first pots were ceramic.
5. Step 5. Saucepan — has part — Pot lid. A cap.
6. Step 6. Pot lid — is part of — Petri dish. A cap.

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