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Category: physics

The screech of peeling sticky tape conceals a rapid train of tiny shockwaves, ultrafast imaging shows

A new experiment has uncovered the mechanism responsible for the screeching sound made by peeling sticky tape. Using a combination of ultrafast imaging and synchronized acoustic recordings, Sigurdur Thoroddsen and colleagues at King Abdullah University of Science and Technology have shown that the noise is produced by a rapid train of tiny shockwaves, released through a specialized form of stick–slip motion. The research is published in Physical Review E.

If you’ve ever used sticky tape, you’ll probably be all too familiar with the harsh sound it makes as it peels away from a surface. Yet despite decades of experimental scrutiny, physicists have yet to fully explain the origins of this intriguing acoustic effect.

Previous studies established that peeling proceeds via a “stick–slip” mechanism—a jerky motion characterized by brief, rapid accelerations interrupted by sudden stops. Similar dynamics underpin phenomena ranging from earthquakes to the squeak of basketball shoes on a polished wooden court. However, the fine details of how this process unfolds in peeling tape turned out to be more complex than they first appeared.

Tackling industry’s burdensome bubble problem

In industrial plants around the world, tiny bubbles cause big problems. Bubbles clog filters, disrupt chemical reactions, reduce throughput during biomanufacturing, and can even cause overheating in electronics and nuclear power plants. MIT Professor Kripa Varanasi has long studied methods to reduce bubble disruption.

In a new study, Varanasi, along with Ph.D. candidate Bert Vandereydt and former postdoc Saurabh Nath, have uncovered the physics behind a promising type of debubbling membrane material that is “aerophilic”—Greek for “air-loving.” The material can be used in systems of all types, allowing anyone to optimize their machine’s performance by breaking free from bubble-borne disruptions.

“We have figured out the structure of these bubble-attracting membrane materials to allow gas to evacuate in the fastest possible manner,” says Varanasi, the senior author of the study.

Why you can’t tie knots in four dimensions

We all know we live in three-dimensional space. But what does it mean when people talk about four dimensions? Is it just a bigger kind of space? Is it “space-time,” the popular idea which emerged from Einstein’s theory of relativity?

If you have wondered what four dimensions really look like, you may have come across drawings of a “four-dimensional cube.” But our brains are wired to interpret drawings on flat paper as two-or at most three-dimensional, not four-dimensional.

The almost insurmountable difficulty of visualizing the fourth dimension has inspired mathematicians, physicists, writers and even some artists for centuries. But even if we can’t quite imagine it, we can understand it.

Why Does This Galaxy Have Tentacles? Deep Space Mystery Stuns Astronomers

A newly discovered jellyfish galaxy, seen as it existed 8.5 billion years ago, is challenging assumptions about conditions in the early universe. Astrophysicists at the University of Waterloo have identified a newly discovered jellyfish galaxy that is now the most distant example of its kind ever

Biology, not physics, holds the key to reality

Three centuries after Newton described the universe through fixed laws and deterministic equations, science may be entering an entirely new phase.

According to biochemist and complex systems theorist Stuart Kauffman and computer scientist Andrea Roli, the biosphere is not a predictable, clockwork system. Instead, it is a self-organising, ever-evolving web of life that cannot be fully captured by mathematical models.

Organisms reshape their environments in ways that are fundamentally unpredictable. These processes, Kauffman and Roli argue, take place in what they call a “Domain of No Laws.”

This challenges the very foundation of scientific thought. Reality, they suggest, may not be governed by universal laws at all—and it is biology, not physics, that could hold the answers.

Tap here to read more.

The Color of Wonder and the Chemical Code of Creation

This essay is adapted from Traversal.

We look at a thing — a bird, a ball, a planet — and perceive it to be a certain color. But what we are really seeing is the color that does not inhere in it—the portion of the spectrum it shirks, the wavelength of light it reflects back unabsorbed. Our world appears a swirling miracle of blue, but its blueness is only a perceptual phenomenon arising from how our particular atmosphere, with its particular chemistry and its insentient stubbornness toward a particular portion of the spectrum, absorbs and reflects light.

In the living world beneath this atmosphere that scatters the shorter wavelengths as they pass, blue is the rarest color: There is no naturally occurring true blue pigment among living creatures. In consequence, only a slender portion of plants bloom in blue, and an even more negligible number of animals are bedecked with it, all having to perform various tricks with chemistry and the physics of light, some having evolved astonishing triumphs of structural geometry and optics to render themselves blue. Each feather of the blue jay is tessellated with tiny light-reflecting beads arranged to cancel out every wavelength of light except the blue.

The physics of sneaker squeaks: High-speed imaging shows how they arise from supersonic detachment pulses

Basketball shoes on a gym floor, bicycle brakes in need of a tune-up, or the squeal of tires are everyday examples of squeaking sounds. Such sounds have long been attributed to stick-slip friction, or a cycle of intermittent sticking and sliding between surfaces. While this framework explains many rigid-on-rigid systems such as door hinges, it does not fully capture the physics of soft-on-rigid interfaces, like shoes on a floor.

To shed light on this little-understood physical process, researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), in collaboration with the University of Nottingham and the French National Center for Scientific Research, have used high-speed imaging to investigate the dynamics of soft solids sliding rapidly on rigid substrates.

In a study published in Nature, the team led by first author Adel Djellouli, a postdoctoral fellow in the lab of Katia Bertoldi, the William and Ami Kuan Danoff Professor of Applied Mechanics at SEAS, reports that squeaking emerges from a previously unseen mechanism.

Physicists develop new method to measure universe’s expansion rate

We have known for several decades that the universe is expanding. Scientists use multiple techniques to measure the present-day expansion rate of the universe, known as the Hubble constant. These methods are internally consistent and based on the same physics, so all observed values of the Hubble constant should agree. But those that come from early-universe datasets disagree with those that come from late-universe datasets. This problem is known as the Hubble tension and is considered to be one of the most significant open questions in cosmology.

Now a team of astrophysicists, cosmologists, and physicists at The Grainger College of Engineering at the University of Illinois Urbana-Champaign and at the University of Chicago has developed a novel way to compute the Hubble constant using gravitational waves—tiny ripples in the spacetime fabric. The researchers were able to improve upon the accuracy of prior gravitational-wave methods of measuring the Hubble constant. As our capability to observe gravitational waves improves in the future, this new method can be used to make even more accurate measurements of the Hubble constant, bringing scientists closer to resolving the Hubble tension.

Illinois Physics Professor Nicolás Yunes said, “This result is very significant—it’s important to obtain an independent measurement of the Hubble constant to resolve the current Hubble tension. Our method is an innovative way to enhance the accuracy of Hubble constant inferences using gravitational waves.” Yunes is the founding director of the Illinois Center for Advanced Studies of the Universe (ICASU) on the Urbana campus.

Physicists watch light drift in quantized steps for the first time

In physics, the classical “Hall effect,” discovered in the late 19th century, describes how a transverse voltage is generated when an electric current is exposed to a perpendicular magnetic field. Simply put, the magnetic field causes the electrons, which are negatively charged, to drift sideways, creating a negative charge on one edge of the conducting strip and a positive charge on the opposite side.

For decades, this voltage difference has been used as a diagnostic tool to measure magnetic fields with precision and characterize material doping levels, that is, the addition of a tiny, controlled amount of impurity to a pure material to change how it conducts electricity.

In the 1980s, experiments at ultra-low temperatures with ultra-thin conductors—imagine a sheet of paper—revealed that under intense magnetic fields, this voltage difference increases not in a straight line but in perfectly defined steps.

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