Useful changes we engineer

We use changes deliberately to make life better:

• Cooking: chemical change transforms raw ingredients into digestible, flavourful food.
• Fermentation: microbes turn milk into curd, grapes into wine, dough into bread.
• Baking: yeast + heat → spongy bread (gas bubbles trapped inside).
• Smelting: heat iron ore + carbon → pure iron (chemical change).
• Generating electricity: burning fuels or using chemical cells.
• Refrigeration: slow down chemical spoilage with cold.

Nature also uses changes constantly: photosynthesis, decay of leaves to soil, formation of fossil fuels over millions of years.