What is an example of a physical change to hair?

A physical change to hair refers to a change that alters the form or appearance of the hair without affecting its chemical structure. Hair cutting exemplifies this concept perfectly, as it involves removing length from the strands and shaping the hair, but does not alter the hair's chemical composition. The results are immediately visible, and once the hair is cut, it maintains its original color and texture.

Dyeing, perming, and bleaching all involve chemical processes that change the molecular structure of the hair. Dyeing changes the color of the hair by adding pigments, perming alters the hair's texture and shape through chemical reactions, and bleaching lightens the hair by stripping it of its natural pigments. These processes create lasting effects that affect the hair in deeper ways than just a change in appearance. Thus, hair cutting stands out as a pure physical change, focused solely on altering the length and style without any chemical alteration.