Drum brake and petri dish: what they have in common

1. Step 1. Drum brake — uses — Friction. The shoes brake by friction.
2. Step 2. Friction — is used in — Quern. Grain is crushed and ground by the friction of the stones.
3. Step 3. Quern — is used in — Bread. Flour was ground on millstones.
4. Step 4. Bread — uses — Fermentation. Yeast dough rises through fermentation.
5. Step 5. Fermentation — is used in — Antibiotic. Penicillin is produced by fermentation.
6. Step 6. Antibiotic — uses — Petri dish. Fleming noticed mould in a Petri dish.

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