That weird phenomenon found in your sink has finally been explained

8 Aug 2018

A hydraulic jump seen in a sink. Image: graalz/Shutterstock

Something weird happens every day in your sink, and physicists finally think they have an answer for the ‘hydraulic jump’.

Perhaps unbeknownst to the vast majority of people, a mysterious physics phenomenon occurs every time you turn on your tap in a sink.

Whether it’s brushing your teeth or just getting some water, you will notice how, when the water hits the sink, it splays out leaving a somewhat hollow ring.

First described by Leonardo da Vinci in the 1500s, this phenomenon is referred to as a hydraulic jump and its cause has frustrated scientists for centuries.

Since the 1820s, it was believed that hydraulic jumps are the result of the gravitational pull of the Earth, but that has since been disproved.

Now, new research conducted by a team from the University of Cambridge may have finally revealed an answer.

In a paper published to the Journal of Fluid Mechanics, Rajesh Bhagat and his team described how they fired jets of water upwards and sideways on to flat surfaces. In doing so, the team saw the same hydraulic jumps occur as if the water was flowing downwards.

Suspecting it could be caused by a combination of surface tension and viscosity, Bhagat and the team altered these attributes of water to accurately predict the size of hydraulic jumps, regardless of which direction the water was moving. In doing so, they disproved the 200-year-old gravitational theory.

Major implications for industry

Prof Paul Linden, one of the authors of the paper, described the discovery as “groundbreaking”.

“[Bhagat’s] experiments and theory show that the surface tension of the liquid is the key to the process and this has never before been recognised, even though the problem was discussed by da Vinci and many others since.

“This work represents a remarkable achievement in our understanding of the dynamics of thin layers of fluid.”

While the discovery is unlikely to change the life of the average person, it will have major implications for industry where hydraulic jumps exist on a grander scale.

“Understanding this process has big implications and could reduce industrial water use dramatically,” Linden said.

“The new theory is already being used in practical work in the chemical engineering department. People can use this theory to find new ways to clean everything from cars to factory equipment.”

Colm Gorey was a senior journalist with Silicon Republic