structure , ▁such ▁as ▁mud s , ▁sl ud ges , ▁susp ensions , ▁polym ers ▁and ▁other ▁glass ▁form ers ▁( e . g ., ▁sil ic ates ), ▁as ▁well ▁as ▁many ▁food s ▁and ▁add it ives , ▁bod ily ▁flu ids ▁( e . g ., ▁blood ) ▁and ▁other ▁bi ological ▁materials , ▁and ▁other ▁materials ▁that ▁belong ▁to ▁the ▁class ▁of ▁soft ▁matter ▁such ▁as ▁food . ▁ ▁Newton ian ▁flu ids ▁can ▁be ▁character ized ▁by ▁a ▁single ▁coefficient ▁of ▁vis cos ity ▁for ▁a ▁specific ▁temperature . ▁Although ▁this ▁vis cos ity ▁will ▁change ▁with ▁temperature , ▁it ▁does ▁not ▁change ▁with ▁the ▁stra in ▁rate . ▁Only ▁a ▁small ▁group ▁of ▁flu ids ▁exhib it ▁such ▁constant ▁vis cos ity . ▁The ▁large ▁class ▁of ▁flu ids ▁whose ▁vis cos ity ▁changes ▁with ▁the ▁stra in ▁rate ▁( the ▁relative ▁flow ▁velocity ) ▁are ▁called ▁non - New ton ian ▁flu ids . ▁ ▁R he ology ▁generally ▁accounts ▁for ▁the ▁behavior ▁of ▁non - New ton ian ▁flu ids , ▁by ▁character izing ▁the ▁minimum ▁number ▁of ▁functions ▁that ▁are ▁needed ▁to ▁relate ▁str esses ▁with ▁rate ▁of ▁change ▁of ▁stra in ▁or ▁stra in ▁rates . ▁For ▁example , ▁k etch up ▁can ▁have ▁its ▁vis cos ity ▁reduced ▁by ▁sh aking ▁( or ▁other ▁forms ▁of ▁mechanical ▁ag itation , ▁where ▁the ▁relative ▁movement ▁of ▁different ▁layers ▁in ▁the ▁material ▁actually ▁causes ▁the ▁reduction ▁in ▁vis cos ity ) ▁but ▁water