Look into your bowl of cereal when the last remaining chunks of cereal remain. Do it! Those last bit of Rice Krispies, Fruit Loops or Cap'n Crunch are floating to the top doing waiting for you to put that bit of sugary goodness into your mouth. Before your shove that food into your face did you stop to think? Why is my Cap'n Crunch floating together like those garbage piles floating in the Pacific? You have a great big bowl. Why is it not randomly dispersed around the bowl to increase its entropy?
The last pieces of cereal always clump together in milk due to surface tension interactions of the milk hitting the side of the bowl. The side of your IKEA bowl (I just know you shop there) is made of ceramic. Milk adjacent to the side of a container curves either upward or downward, depending on whether the liquid is attracted to or repulsed by the material of the wall. Since milk in this case is attracted to ceramic, the water surface in this container will curve upwards near the container walls, as this shape increases the contact area between the water and the ceramic. Dense objects like Cap'n Crunch or garbage can rest on liquid surfaces due to surface tension. These objects deform the liquid surface downward. Other dense objects, seeking to move downward (to the middle of your bowl) but constrained to the surface by surface tension, will be attracted to the first. Objects with an irregular meniscus (since the Cap'n Crunch is rough) also deform the water surface, forming "capillary multipoles". When such objects come close to each other, they first rotate in the plane of the water surface until they find an optimum relative orientation. Subsequently they are attracted to each other by surface tension.
This is explained by Dominic Vella and L. Mahadevan of Harvard University (scientists actually study this but they used Cheerios instead.
where γ is the surface tension, K1 is a modified Bessel function of the first kind, B = ρgR2 / γ is the Bond number, and
is a nondimensional factor in terms of the contact angle θ. This a convenient meniscus length scale:
Useful references taken from Wiki:
- "Scientists explain the 'Cheerio Effect'". MSNBC. http://www.msnbc.msn.com/id/9425907/. Retrieved 2006-08-28.
- Chan, D.Y.C.; Henry, J.D.; White, L.R. (1979). "The interaction of colloidal particles collected at the fluid interface". Journal of Colloid and Interface Science 79 (9): 410–418.
- Stamou, D.; Duschl, C.; Johannsmann, D. (2000). "Long-range attraction between colloidal spheres at the air–water interface: The consequence of an irregular meniscus". Physical Review E 62 (4): 5263–5272. doi:10.1103/PhysRevE.62.5263.
- Vella, D.; Mahadevan, L. (September 2005). "The Cheerios effect". American Journal of Physics 73 (9): 817–825. doi:10.1119/1.1898523.
Disclaimer: I hate Cap'n Crunch because it is not crunchy enough and is not really so healthy for any meal of the day. So Captain Horatio Crunch can suck it. Rice Krispies so much better. The Rice Krispies treats very delicious. Snap, Krackle and Pop should sink Cap'n Crunch's fictitious boat. Seriously ironically!!