What do you call the video effect where water looks like it's standing still when filmed

Question

I found a few interesting effects, which was labelled under the rolling shutter effect, however I was told that this was NOT an example of rolling shutter effect, what would you call this effect?

The question is 3 fold: I heard they used this effect in movies, which ones, an example clip would be nice, what do they officially call it, and why does this happen?

These are the examples I am referring to:
REALLY interesting effects:
For example, the water looks like its static. [PetaPixel][1] explains it; "by pressing a water tube against a speaker, bibio was able to control the vibration frequency of the water flowing through the tube. He then adjusted the pulses of the water to match up with the frame rate of his Canon 5D Mark II."

Another example was the static helicopter:

Answer 1

This is called stroboscopic effect. It refers to when the sample rate is synchronized or very slightly out of sync resulting in a much slower representation of the motion that results from taking a picture that is at the same point or slightly advanced point in a subsequent cycle of a higher frequency cyclic motion.

You can actually do the same exact thing in real life for your own eyes by using a strobe light, which is the more common demonstration, though frame rate can be used too if you can adjust it closely enough.

Answer 2

I'm unsure if there is a specific "official" word for this effect. I guess I would call it frequency synchronisation.

This effect appears whenever the framerate (e.g. frequency your camera takes a picture) of you camera matches the frequency of another recurring action. It doesn't have to be the exact same frequency but a multiple of it. So if the rotor of the helicopter is turning at 50 rotations per seconds, filming this with 25 fps would theoretically be enough for the effect to appear (not accounting for motion blur and other artifacts when dealing with fast moving objects). So the camera always captures a frame when the moving object completed a full movement giving the illusion that it doesn't move because we only capture it every time its at a specific position. Being slightly over or under the frequency of the object will make it look like its moving in slow motion forwards or backwards because we only increment in the position by tiny amounts.

The movement has to be an exact recurring loop, otherwise this can not work.

In movies you can see this in tire movement but usually its not a desired effect, I haven't seen a movie where is effect was deliberately used.