I was recently introduced to the liquid rope coil effect by this video:
https://www.youtube.com/watch?v=zz5lGkDdk78
I noticed while the video mentioned the equations governing the motion, it didn't really talk about the reason for the effect. All it really said was that the honey is flowing too fast so it needs to get out of the way of itself.
I also looked at any papers I could find on the subject, and while many have a mathematical model for what's happening and the speed the coils are formed, I couldn't find any intuitive explanation for why/how the coils are formed in the first place.
So in particular, below are the things I don't understand about the effect. I would appreciate help with understanding either of these questions.
Why does it fall in a circle pattern? Is it that once the honey has been displaced a bit from the center and has some tangential velocity, it experiences a viscous force towards the center (and also upwards, but gravity counteracts that) from the honey above it which causes it to move into a circle?
Why does it start to coil? If the honey is dropping, obviously it starts out by moving straight down. I can imagine how once some honey falls in the middle, the next honey that falls will fall on the middle and then slide off the middle column and fall outwards. So at this point we have our stream slightly displaced from the middle but has no tangential velocity. What effect gives the stream a tangential velocity so it can start to move circularly?
Best Answer
the coil effect only works when you have high viscous fluids like honey. It doesn't work with a low viscous fluid because the low viscous fluid flows faster than the honey, making the fast flowing fluid like water to not have the rope coiling effect