Undergrad What is causing those patterns on the glass?

[John Morax]

I couldn't come up with a satisfying explanation myself so I figured this is where I might find an answer.. I have been drinking smooth yogurt of this glass, after I drunk it I left the glass on the side and after few minutes this pattern appeared on the inside of the glass. I know it comes from the left over yogurt slowly sliding down the bottom of the glass after I raise it to drink. But why this pattern? Why the liquid doesn't slide uniformly along the surface of the glass? What's gravity doing here? I have tried again and the same patterns appears. Sorry if this sounds like a silly question, but I fell like something intriguing is happening here... Call me crazy but I fantasized about cluster of galaxys and space time itself while looking at it...

Thank you very much to anyone that will be so kind to shine some light on this problem.

 

[Ibix]

Almost certainly there are microscopic scratches in the surface of the glass. When there's only a thin film of yogurt they are big enough to deflect the flow. So you'll see similar patterns time and again because the scratches are always there, but they'll evolve as your glass acquires more tiny scrapes from your dishwasher or whatever.

You might be able to see the scratches with a strong hand lens.

 

[FilipLand]

It's because you don't have an ideal glass, nor an ideal liquid,, nor noninteracting particles, your glass had dried leftovers and dirt, causing the liquid not to cross those paths. And why it doesn't cross those paths is because of chemical forces and to some extent friction combined with the principle of least action.

If you pour water on a very odd and hilly surface the you will not get a smooth plane/layer of water over it.

If you neglect the fact that particles interact and distribute them through a ideal surface it would be somewhat distributed uniformly.

 

[256bits]

What's gravity doing here?

Gravity not doing anything except causing the flow/
You have precipitation of the suspended solid particles on the glass forming patterns.
As already stated,
It can be attributed to the uneven surface of the glass, impurities on the glass rendering it hydrophobic or not.
Water droplets running down glass exhibit similar features in that they do not fall straight down but meander.

In this case, there also is a changing viscosity of the smoothie as it leaves particles behind, forming fractal patterns.
https://www.researchgate.net/publication/1825859_Fractal_Behavior_of_Flow_of_an_Inhomogeneous_Fluid_Over_a_Smooth_Inclined_Surface

 

[John Morax]

Thank you everybody for the explanations. There must be impurities distributed on the glass and traces of chemicals from the dishwasher. I do also understand clearly that the principle of least action is at work.
...still such a cool pattern is it? It looks like the estuary of a river.
Thanks again to all.