2

I was making coffee for myself, when I observed that when I poured coffee from the frying pan (having curved edges), the fluid went directly into the cup without falling; but when I transferred coffee from one cup to another at a particular inclination, the fluid ran down the edge of the cup in straight line rather than going directly into the other cup.

Question: why did the fluid run down the edge of the cup rather than directly falling into the other cup due to gravity?

Observation It has something to do with the shape as both the containers had different edges: one was round and other was bulging out.

Qmechanic
  • 220,844
imposter
  • 1,200

1 Answers1

2

I suspect it has to do with the edge of the cup you were using to transfer the liquid and the adhesive forces between the liquid and the cup. When the cup is tilted at an angle lesser than, say, $\theta_\text{max}$, the relevant component of the weight of the liquid moving out from the cup is not sufficient to outweigh the adhesive forces between the cup and the liquid, causing the liquid to run down the edge.

On the other hand, at sufficiently large angles $\theta > \theta_\text{max}$, the weight component is large enough to direct the liquid straight into the second cup without adhesion. The overall effect of the adhesive force depends on the edge of the cup: curvy edges change the direction of said force and might affect the results.

Yejus
  • 2,136