I will write a program about principle bernoulli, but i have a problem. My input data: Pressure(p1) = 1000 Cross-section(A1) = 1 Velocity(V1) = 1 Cross-section(A2) = 0.5 Velocity(v2)= (V1A1)/A2 to simplify: h1=h2 i'm counting the pressure p2 : p2 = p1 + 0.5*v1*v1 - 0.5*v2*v2 , so i getting negative pressure.. This is a problem (negative pressure) I'm trying to add atmospheric pressure, but it doesn't solve my problem. Is a mathematical formula is good? Is there any other relationship?