This opposition would not occur if the tubes were merely capped off at the ends and filled with
stagnant water. If this were the case, the tubes would simply be heavy with the water’s weight,
and they would rotate freely about the axis just like any pair of heavy metal tubes would (whether
hollow and filled with water, or solid metal). The tubes would have inertia, but they would not
actively oppose any external effort to rotate.
Having liquid water move through the tubes is what makes the difference, and the reason becomes
clear once we imagine what each water molecule experiences as it flows from the center (axis of
rotation) to the nozzle at the tube tip. Each water molecule originating from the center begins with
no lateral velocity, but must accelerate as it travels farther along the tube toward the circumference
of the tips’ rotation where the lateral velocity is at a maximum. The fact that new water molecules
are continually making this journey from center to tip means there will always be a new set of water
molecules requiring acceleration from center velocity (zero) to tip velocity (maximum). In capped
tubes filled with stagnant water, the acceleration would only occur in getting the tubes’ rotation up
to speed – once there, the lateral velocity of each water molecule sitting stagnant inside the tubes
would remain the same. However, with water flowing from center to tip, this process of acceleration
from zero velocity to tip velocity must occur over and over again (continually) for each new water
molecule flowing through. This continual acceleration of new mass is what generates the Coriolis
force, and what actively opposes any external force trying to rotate the “anti-rotating” sprinkler.
As you might guess, it can be difficult to engineer a tubing system capable of spinning in circles
while carrying a flowstream of pressurized fluid. To bypass the practical difficulties of building a
spinning tube system, Coriolis flowmeters are instead built on the principle of a flexible tube that
oscillates back and forth, producing the same effect in a cyclic rather than continuous fashion. The
effect is not unlike shaking a hose side to side as it carries a stream of water