The official explanation for this problem appears to me to be incorrect.
Here is the video I watched before creating this one(go watch it first ideally): • How Physicists FINALLY...
Here is the answer as currently given on Wikipedia:
The behavior of the reverse sprinkler is qualitatively quite distinct from that of the ordinary sprinkler, and one does not behave like the other "played backwards". Most of the published theoretical treatments of this problem have concluded that the ideal reverse sprinkler will not experience any torque in its steady state. This may be understood in terms of conservation of angular momentum: in its steady state, the amount of angular momentum carried by the incoming fluid is constant, which implies that there is no torque on the sprinkler itself.
Alternatively, in terms of forces on an individual sprinkler nozzle, consider Mach's illustration. There is:
the reaction force on the nozzle as it sucks in the fluid, pulling the nozzle anti-clockwise;
the inflowing water impacting on the inside of the nozzle, pushing the nozzle clockwise.
These two forces are equal and opposite, so sucking in the fluid causes no net force on the sprinkler nozzle. This is similar to the pop pop boat when it sucks in water-the inflowing water transfers its momentum to the boat, so sucking in water causes no net force on the boat.
Many experiments, going back to Mach, find no rotation of the reverse sprinkler. In setups with sufficiently low friction and high rate of inflow, the reverse sprinkler has been seen to turn weakly in the opposite sense to the conventional sprinkler, even in its steady state. Such behavior could be explained by the diffusion of momentum in a non-ideal (i.e., viscous) flow. However, careful observation of experimental setups shows that this turning is associated with the formation of a vortex inside the body of the sprinkler. An analysis of the actual distribution of forces and pressure in a non-ideal reverse sprinkler provides the theoretical basis to explain this:
Differences in the regions over which internal and external forces act constitute a force-couple with different moment arms consistent with reverse rotation. the resulting flow-field asymmetry developed downstream from the sprinkler-arm bends supports the role of vortices in reverse sprinkler rotation by suggesting a mechanism for generating vortices in a consistent direction.
Негізгі бет Feynman's sprinkler solved (correctly?) in Scrap Mechanic
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