3 min readHere’s what you’ll learn when you read this story:
- Today, scientists don’t discover “laws” but instead perfect theories, always aware that there’s more to learn.
- A new study shows why centuries-old “laws” need some tweaking, as a 300-year-old law of friction fails to predict interactions between two magnetic materials.
- Understanding this physics-based exception could help improve micro- and nano-devices that rely on magnetism to function.
Today, scientists aren’t in the habit of creating “laws.” Sure, we still refer to scientific breakthroughs of centuries past as “laws,” chief among them being Isaac Newton’s laws of motion, among many others. But as science has matured, we’ve come to learn that these laws are far from inviolable. Newton’s laws of motion, for example, break down at extreme scales, which is where Albert Einstein’s general theory of relativity comes in.
Now a team of scientists at the University of Konstanz in Germany have once again proven why the word “theory,” which allows some flexibility for future discoveries, replaced “laws” in today’s scientific parlance. The law in question is Amontons’ first law of friction. Postulated by French physicist Guillaume Amontons in the treatise De la résistance causée dans les machines in 1699, the idea is pretty intuitive: “The force of friction is directly proportional to the applied load.” This simply means that a heavier object (say a couch) is going to exert higher friction than something lighter (a chair). This is because tiny deformations in materials increase in contact under heavier loads, which in effect enhances friction.
But in a new study published in the journal Nature Materials, researchers discovered that this law breaks down when considering magnetic materials. In an experiment, the authors used a two-dimensional array of freely rotating magnetic elements above a second magnetic layer. Although these materials never come into contact, there is measurable magnetic friction between the two.
“By changing the distance between the magnetic layers, we could drive the system into a regime of competing interactions where the rotors constantly reorganize as they slide,” said Hong Kong University of Science and Technology’s Hongri Gu, who co-authored this research while at the University of Konstanz.
What the researchers discovered is that at close and far distances, friction was at its weakest, but it actually increased at intermediate distances. That’s because at these medium distances, competing interactions take over. For example, in the top magnetic layer, magnetic moments point in parallel but opposite directions, which is known as “antiparallel alignment,” while the bottom layer flows into a same-direction parallel alignment. This unstable configuration causes increased magnetic friction as the materials are forced to constantly switch between parallel and antiparallel states.
“What is remarkable is that friction here arises entirely from internal reorganization,” University of Konstanz’s Clemens Bechinger, supervisor on the project, said in a press statement. “There is no wear, no surface roughness, and no direct contact. Dissipation is generated solely by collective magnetic rearrangements.”
Of course, this experiment wasn’t designed just to prove Amontons wrong (after all, his laws do work remarkably well under normal circumstances), but whatever magnetic behaviors occur at these macroscales likely can occur under microscopic ones as well, potentially unlocking a range of micro– and even nanoelectromechanical devices, including magnetic bearings and atomically thin magnets.
Once again, science proves why there’s not such a thing as a “law”—because there’s always more to learn.
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Darren lives in Portland, has a cat, and writes/edits about sci-fi and how our world works. You can find his previous stuff at Gizmodo and Paste if you look hard enough.