A fluid of a constant density flows through a reduction in a pipe. Find an equation for the difference in pressure, $p_1-p_2$ in terms of $v_1,A_1,A_2,$ and the density, $.$ The constants $A_1$ and $v_1$ are typed with the lower case letters $"A"$ and $"v",$ respectively, followed by the number $"1".$ Similarly for $A_2.($Greek letters should be spelled out, for example, type "rho" without the quotations for $.)$