Pressure force on a control volume

[princejan7]

Homework Statement

http://postimg.org/image/4a8sv6umh/

Why do the pressure forces due to p1 and p2 act in the same direction?

Homework Equations

The Attempt at a Solution

I thought that, given the direction of the flow, the pressure force on the bottom and top would act in opposite directions

 

[Chestermiller]

The region outside the control volume exerts a pressure force on the region inside the control volume at two locations. The pressure at the top is pushing the fluid into the control volume. The pressure at the bottom is trying to keep the fluid from coming out of the control volume. Both these pressures act in the same direction (from outside the control volume to inside the control volume).

Chet