▁ ▁An ▁Ide al ▁Fl uid ▁is ▁a ▁fluid ▁that ▁has ▁no ▁vis cos ity , ▁means ▁it ▁will ▁offer ▁no ▁resistance , ▁p rag matically ▁this ▁type ▁of ▁fluid ▁does ▁not ▁exist . ▁It ▁is ▁in com press ible ▁in ▁nature . ▁Real ▁flu ids ▁are ▁compress ible ▁in ▁nature . ▁They ▁offer ▁some ▁resistance ▁and ▁thus ▁have ▁vis cos ity . ▁All ▁Fl u ids ▁existing ▁are ▁real ▁flu ids . ▁A ▁Newton ian ▁Fl uid ▁is ▁a ▁fluid ▁whose ▁vis c ous ▁she ar ▁str esses ▁( act ing ▁between ▁different ▁layers ▁of ▁fluid ▁and ▁between ▁the ▁fluid ▁layer ▁and ▁surface ▁over ▁which ▁it ▁is ▁flow ing ) ▁are ▁directly ▁proportional ▁to ▁the ▁rate ▁of ▁change ▁of ▁velocity ▁of ▁the ▁flow ▁of ▁the ▁fluid ▁with ▁respect ▁to ▁the ▁distance ▁in ▁the ▁trans verse ▁direction ▁( distance ▁measured ▁per pend icular ▁to ▁the ▁flow ), ▁also ▁known ▁as ▁velocity ▁gradient . ▁The ▁constant ▁of ▁proportional ity ▁is ▁known ▁as ▁the ▁dynamic ▁vis cos ity ▁of ▁the ▁fluid ▁denoted ▁by ▁' μ '. ▁The ▁functional ▁relationship ▁between ▁vis c ous ▁she ar ▁stress ▁and ▁velocity ▁gradient ▁is ▁linear ▁in ▁a ▁Newton ian ▁fluid . ▁This ▁relationship ▁may ▁be ▁written ▁as ▁: ▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁ ▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁ ▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁ ▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁ ▁ ▁Where ▁ ▁= ▁vis c ous ▁she ar ▁stress ▁▁▁▁▁▁▁▁▁▁▁▁▁ ▁= ▁dynamic ▁vis cos ity ▁of ▁the ▁fluid ▁▁▁▁▁▁▁▁▁▁▁▁▁ ▁= ▁velocity ▁gradient ▁across ▁the ▁flow ▁ ▁A ▁Non - New ton ian ▁fluid ▁is ▁a ▁fluid ▁which ▁is ▁different ▁from ▁the ▁Newton ian ▁fluid ▁as ▁the