Why we always spill tea

Why we always spill tea
Jets of colored water are shot onto a vertical cylinder and form a helix-shaped pattern. Credit: University of Amsterdam

Who has never spilled water, tea or wine while pouring it? Pouring liquids is difficult because they tend to cling to the bottle or the teapot spout rather than flowing directly into your cup or glass. A team of scientists from the University of Amsterdam, University of Twente and Saxion University of Applied Sciences put a new spin on this annoying 'teapot effect' by using it to form liquid helices. Their results were published in Physical Review Letters this week.

Despite its ubiquity, understanding the effect has proven particularly difficult. Almost three centuries after the first study, it is nowadays accepted that the adhesion between the liquid and the solid comes from the combination of wetting and the presence of a depression in the fast turning liquid – similar to the one above airplane wings that allows the plane to fly. However, no theory has been able to capture exactly when the clinging occurs.

Helix-shaped swirls

By shooting jets of water onto vertical cylinders, the researchers observed that the liquid can cling to the cylinder, just like it clings to your teapot. Because of the clinging effect, the water swirls around the to form a helix. By modeling the helix shape and how it is formed, the team was then able to predict the exact clinging behaviour for the first time.

Because this type of clinging occurs every time a liquid stream must detach from a solid, the result can not only be used to make teapots that don't spill as much – it will also be useful for many , ranging from pouring to 3-D printing.


Explore further

Solving Teapot Effect

More information: E. Jambon-Puillet et al. Liquid Helix: How Capillary Jets Adhere to Vertical Cylinders, Physical Review Letters (2019). DOI: 10.1103/PhysRevLett.122.184501
Journal information: Physical Review Letters

Citation: Why we always spill tea (2019, May 9) retrieved 21 May 2019 from https://phys.org/news/2019-05-tea.html
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May 09, 2019
Why do we spill tea? Because, Max Ent, there are more ways to spill tea than to not spill tea. How skilled is a sharpshooter, Max Ent, there are millions more ways to miss than to hit.

May 09, 2019
As a Brit who drinks many cups of tea per day, I have long believed that the ultimate test of a robot dexterity would be to pick up a fine handled cup of tea, walk down some stairs, and then hand it to another robot that then drinks it, all without spilling the tea. I offer this 'Brit-test' patent-free to the robot community.
I also know that the best non-spill teapots have a spout end shaped like a vertically opened bird's beak, presumably using surface tension to direct the tea to hug the pointed end of the spout.

May 10, 2019
...using surface tension to direct the tea to hug the pointed end of the spout.
As a submarine sailor I learned to use butter or, if no one was looking, facial oil wiped under a spout to minimize surface tension and pour drip free.

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