What makes a fluid flow?

There are basically two ways to make fluid flow through a pipe.

  1. Tilt the pipe and let gravity pull the fluid downhill.
  2. Make the pressure higher at one end of the pipe than the other. A pressure difference is equivalent to a net force, accelerating the fluid toward lower-pressure regions.

In our tube of varying cross-section, where is the pressure greatest?

  1. At the ends, where the tube is wide
  2. In the middle, where the tube is narrow