Final answer:
Both rust forming on a bicycle frame and baking cookies are examples of irreversible changes, where new substances are formed that cannot easily revert to their original forms.
Step-by-step explanation:
The common factor between rust forming on a bicycle frame and baking cookies is that both are irreversible changes. The process of rust formation involves the iron in the bicycle frame reacting with oxygen and water, which is a chemical reaction known as oxidation, resulting in a new substance, iron oxide or rust, which cannot be easily reverted back to iron. Similarly, baking cookies induces chemical reactions between ingredients that result in a baked product that cannot be returned to its original form of raw dough and separate ingredients.