As you found out in the previous part, Bernoulli's equation tells us that a fluid element that flows through a flow tube with decreasing cross section moves toward a region of lower pressure. Physically, the pressure drop experienced by the fluid element between points 1 and 2 acts on the fluid element as a net force that causes the fluid to .

Increase in speed.

Explanation: Since mass must be conserved, if the cross section of the flow tube is not the same, that is varies, the flow speed must change to conserve mass.

This means that there is a non-zero net force acting on the fluid that causes the fluid to increase or decrease in speed depending on whether the fluid is flowing through a portion of the tube with a smaller or larger cross

the independent variable, or the one that is intentionally manipulated is the speed.