# Does this water effect require wind?

http://wins.failblog.org/2012/07/05/epic-win-photos-book-fountain-win/

It’s a water sprinkler attached to a sculpture of an open book, such that the water has the appearance of a page being turned. It’s not just that the water goes back and forth–the water stream is rigged somehow to appear to “bend” far to the left of the sprinkler’s rotating cycle, giving the “page turning” effect that much more realism.

I’ve seen water sprinklers of course, but to my recollection, when the sprinkler is pointing straight up, the water goes straight up and down, regardless of the momentum of the rotating sprinkler itself.

Am I right to think that the effect in the animated gif would only work in the presence of wind?

Looks similar to a normal lawn sprinkler to me. Maybe a faster gearing to give it more oomph as it moves to the left.

I don’t think so, but I can’t really defend my position. I really just wanted to say that’s an awesome fountain!

It’s hard to visualize what could be happening here since the water gives the illusion of being a solid “pagelike” object. But if I think about the momentum of the individual particles of water (so to speak), it seems like for this fountain to do what it’s doin, bits of water must shoot off to the left–and then fall straight down rather than continuing leftward as they sink. How to account for that change in momentum? (Or am I wrong to think that has to be happening?)

I don’t think so, it’s the rotation of the cylindrical thing in the middle that causes the effect. You can get a similar effect by pivoting the nozzle of your hose.

I don’t think wind is involved. It’s not like the streams of water are static. The flow seems to be slow enough that the streams appear to bend because they are rotating fast enough that the top of the stream is in a different place than the bottom. So unlike a lawn sprinkler, the rotation is noticeably faster than the water flow. It appears that the ‘spray bar’ is just turning in a circle at a steady speed. If you look at a ‘rain bird’ type of sprinkler that shoots water out horizontally you’ll see the same kind of curved effect in the stream if it’s rotating quickly.

I don’t think you are right to think of the water as being divided into “individual particles.” In a stream of water there is molecular cohesion between the molecules, just as there is between the molecules in a sheet of paper or other solid. Of course the cohesion in a liquid is not as strong, and the stream eventually breaks into droplets that move according to the momentum that they have when they separate, but up until then the stream will indeed behave more like a flexible solid than a collection of droplets. It is not an illusion.

I have to admit I don’t really get what you’re describing here. It’s a cool fountain and a neat effect, but to me the water definitely behaves predictably. I don’t see where the “bending” comes in.

I, also, see no bending outside of the usual curve of water falling. As the “page” turns the previously arced water has fallen down and is being replaced by a fresh spray located a bit over the the side.

I see now. There were two conflicting visual intuitions I was victim of–both inaccurate. One was that water sprayed straight up was somehow being “pulled” to the left by the subsequent spray. (Giving rise to the illusion of the page being pulled to the left.) The other was that water being sprayed to the left was somehow falling straight down once it reached a certain point, instead of continuing (as momentum would have it) to the left. (Giving rise to the illusion of the page folding down on the lefthand side.)

After reading what you guys said (except you njtt I think you’re giving the water’s cohesion too much credit :D) I am now able to see it as an arc of water created by the spray which falls and then is replaced by a new arc of water. No water’s being “pulled” or “pushed” to the left or right.