The Physics of Clustering: From Cereal to Insects

While you would expect to learn about about physics in school, one of the least places you would expect to learn physics is on a dining table especially when you are having a plate of cereal. Do you wonder why cereals come together to form a cluster when poured into milk, or why bubbles from beverages or from washing soap will come together to form a clump or cluster, or why paper clips do the same when placed in water, or maybe thumb tacks coming together to form that cluster?

If you do not know why this happens, you do not need to be hard on yourself because even majority of scientists didn't know what it was not until the year 2005 which is very recent in the world of science. In 2005, a pair of mathematician decided to look at these phenomenon and wanted answers.

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First, do you know the way breakfast cereal is made, it is less dense than water? That is why it always stay at the top and when we see milk, it is majorly water so the cereal weighs less than the milk and so the force of buoyancy pushes up each ring until there is an equilibrium to the downward force of gravity. Before you start to look confused, this happens because the surface that interacts with the liquid is curved up giving the meniscus effect which is the same thing that is seen at the edge of a container.

While water molecules are attracted to one another, they are more attracted to the edges of bowls or cups they are poured into or the edge of the cereal or thumb tacks when placed carefully. A buoyant object will always be pushed to the meniscus and that is why they reach for the edge of the glass.

For the case of paper clips that sink when tossed into water, they do not do the same when not tossed. When placed carefully, they float as a result of surface tension and not because they are buoyant. This can be changed when you add something as simple as soap which would change the surface tension, lowering the surface tension of water thereby causing object that rely on surface tension to sink while buoyant objects remain since they do not depend on surface tension.

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Some insects use both surface tension and force of buoyancy to move on water. Insect like water striders are able to float using force of buoyancy and at such can carry themselves and a weight up to 15 times themselves while floating on water, and this is because tiny hairs on their legs trap air bubbles thereby increasing their buoyancy, while insects like water treaders use surface tension to move on water. In other for them to lift themselves, they lift their body to form an arch thereby causing the water to take them to the edge so they can lift.

The seemingly simple act of cereal clustering in milk or bubbles clumping together is rooted in fascinating principles of physics. Buoyancy and surface tension play crucial roles in these everyday phenomena, demonstrating how even the most mundane occurrences are governed by complex scientific principles. So, the next time you pour yourself a bowl of cereal or watch a water strider glide across a pond, you'll understand the intriguing physics at play.

Reference

https://softmath.seas.harvard.edu/wp-content/uploads/2019/10/2005-13.pdf
https://pure.uva.nl/ws/files/169247924/Back_matter.pdf
https://www.annualreviews.org/content/journals/10.1146/annurev.fluid.38.050304.092157
https://thales.mit.edu/bush/wp-content/uploads/2021/04/Bush_Hu_2006.pdf
https://www.nature.com/articles/432036a