Flow of a fluid through a sudden contraction

(a) An incompressible liquid flows through a sudden contraction from a pipe of diameter D₁ into a pipe of smaller diameter D₂. What does the Bernoulli equation predict for P₁ – P₂, the difference between the modified pressures upstream and downstream of the contraction? Does this result agree with experimental observations? 

(b) Repeat the derivation for the isothermal horizontal flow of an ideal gas through a sudden contraction.