Wet hair being set and dried into a temporary new shape is an example of what kind of change?

Setting wet hair and drying it into a new shape (for example, with rollers or a blow-dryer and round brush) is a temporary physical change. The hydrogen bonds in the hair are broken by water and reformed in a new position as the hair dries, holding the style until the hair gets wet or absorbs moisture again, at which point it reverts. This contrasts with permanent chemical changes (like perms or relaxers) that restructure the hair. Recognizing wet styling as a temporary physical change is basic hairstyling science.