The science behind an important unexplained everyday occurrence in our world has finally been described. Called the “teapot effect,” it refers to an experience many of us have probably had: We go to pour a piping hot beverage out of a teapot too slowly, and end up with unwanted tea all over the table.
The history behind the phenomena
First described in 1956 by Israeli scientist Markus Reiner, scientists have actually studied the “teapot effect” for decades. When he emigrated to the US, Reiner became a pioneer of the science of flow behavior, or in more scientific terms ‘rheology.’
Since then, people have tried to precisely explain the physics behind the event, but the forces at play here are more complicated than you would think for a mere teapot! In 1999, researchers won the Ig-Nobel Prize for work on this topic, which is an award to annually celebrate unusual discoveries and progression.
Understanding the spillage
Finally, a team from the Vienna University of Technology has published a paper in the Journal of Fluid Mechanics explaining what is going on. The underside of the teapot, where there is a cutting edge, plays a key role. Here, drop formation happens and it always remains wet. The speed at which the tea is poured influences the size of the drop, and if this speed is lower than a force threshold, the tea dribbles down the side of the teapot.
“Although this is a very common and seemingly simple effect, it is remarkably difficult to explain it exactly within the framework of fluid mechanics,” said Bernhard Scheichl, one of the researchers to finally describe the occurrence. “We have now succeeded for the first time in providing a complete theoretical explanation of why this drop forms and why the underside of the edge always remains wetted.”
The exact forces and mathematics behind this concept are complicated, though the main idea is the interaction of forces between the flow of the liquid and the teapot spout. The key takeaway? It may seem counterintuitive but pour quickly to avoid a spill.
Source study: Journal of Fluid Mechanics – Developed liquid film passing a smoothed and wedge-shaped trailing edge: small-scale analysis and the ‘teapot effect’ at large Reynolds numbers
