90-year-old physicist finds new vibration mode, wind energy solution in bathroom

90-year-old Israeli-American professor of physics Amnon Yariv may have just repeated history by discovering something while in the bathroom. Four years ago, during the COVID-19 pandemic, the physicist first noticed something while taking a shower, which, over years of work, has been confirmed to be a new mode of vibration in nature.

On a hot summer afternoon during the COVID lockdown, Yariv was taking a shower and left the showerhead dangling with the water running. While such an event does not attract our attention, it caught the eye of the National Medal of Science-winning professor who has spent over 70 years studying waves and their properties.

Yariv noticed that the showerhead wasn’t just a flexible fixture in the bathroom but displayed properties of being part of the oscillating system. Legend says that the Greek physicist Archimedes ran immediately out of the bath two millennia ago upon making a ground-breaking observation. The modern-day scientist Yariv was more measured in this approach.

What did Yariv observe?

Yariv noticed that as he increased the water flow, the showerhead oscillated bimodally. In plain speak, this means that the showerhead displayed two different oscillations: one where it was swinging back and forth like a pendulum and the other where it was twisting in two directions.

The intriguing bit was that these two oscillations were in sync, driving each other instead of canceling each other.

“This bimodal oscillation is like an Argentinian tango, where each dancer has to remain completely in sync with the other or else they stumble on each other,” said Yariv in a press release. “The idea that a steady force can be used to excite this kind of entangled bimodal oscillation has never been proposed nor demonstrated.”

The nonagenarian physicist then spent the next few years working out the mathematical models that could explain this behavior.

Standing on the shoulders of giants

Yariv found that to explain the oscillation, he had to rely on the single-mode oscillation model. Proposed by Michael Faraday and then mathematically explained by Lord Rayleigh, the model suggests that natural oscillations have a periodic force driving them.

To simplify, Yariv gave an example of a child on a swing that needs an external push to keep swinging. Typically, a parent or friend provides this push. However, as the child grows, s/he learns to push the swing independently, using their legs or weight.

Back in the bathroom on a hot afternoon in 2020, Yariv saw the showerhead oscillate due to the entangled collaboration of two oscillation modes caused by a system nonlinearity.

Once the showerhead started twisting, the steady force of the water pushed back, generating a periodic force that drove the pendulum’s movement. The pendulum movement, in turn, modulated the showerhead’s twisting action at twice its frequency, as seen in the video above.

The mathematical model explaining the motion has been dubbed Yariv’s groove. It can explain phenomena like a STOP sign fluttering or suspension bridges swinging on windy days. It could have applications in civil engineering and even green energy, helping harness more energy from the wind .

The research also comes with a caveat. “My study only follows the system through the onset of the bimodal oscillation and into the early stage of the unstable oscillation, and stops before the heavy showerhead craters the wall,” added Yariv in the press release . “But the new entangled bimodal oscillation is unstable. It doesn’t reach a steady state. It keeps getting larger.”

The research findings were published in the journal PNAS .