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Tag archives: fluids

Why are rectangular pipes like circular pipes?

Go with the flow. (Courtesy: iStockphoto/Inok)

Go with the flow. (Courtesy: iStockphoto/Inok)

By Matin Durrani

Consider a spherical cow.

No, wait, actually, let’s try something different. Consider a rectangular pipe.

In fact, consider what happens when liquid flows along a rectangular pipe, by which I mean one with a rectangular cross section. The flow’s bound to be asymmetrical, right?

Yes, that’s true, but not always. New research published in Physical Review Letters suggests that for liquid flowing along a rectangular pipe that’s exactly 1.87 times wider than it is high, the flow is entirely symmetrical.

Now, I’ll admit that water flowing along a pipe is probably not something that keeps you awake at night, but the new discovery is weird. In fact, Roberto Camassa from the University of North Carolina, Chapel Hill, who was involved in the study, calls it “bizarre”.


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The July 2015 issue of Physics World is now out

By Matin Durrani

Sometimes, nature does something unexpected – something so rare, transient or remote that only a lucky few of us get to see it in our lifetimes. In the July issue of Physics World, we reveal the physics behind our pick of the weirdest natural phenomena on our planet, from dramatic rogue waves up to 30 m tall, to volcanic lightning that can be heard “whistling” from the other side of the world, and even giant stones that move while no-one is watching. We also tackle tidal bores on rivers and the odd “green flash” that is sometimes seen at sunset.

Plus, we’ve got six fabulous full-page images of a range of weird phenomena, including salt-flat mirrors, firenadoes, “ice towers”, beautifully coloured nacreous clouds, mysterious ice bubbles of gas trapped in columns, as well as my favourite – the delicately wonderful “frost flowers” seen very occasionally on plants.


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The biophysics of Godzilla, skipping stones, Schrödinger in the morning and more


By Hamish Johnston

I’m a bit of a connoisseur of the art of stone skipping. That’s because I grew up a stone’s throw from the western end of Lake Ontario, which thanks to its shale shoreline has the best skipping stones in the world. As a result, I was fascinated to read a piece on the Figure One blog about entitled “Frisbee meets fluid: Skipping stones takes spin and skill”.


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Honey at the asymptotic limit

By Hamish Johnston

What’s the buzz in physics this week? Forget dark matter, it’s honey – or rather the strange properties of this tasty fluid.

If you have a sweet tooth (or an interest in the Rayleigh–Plateau instability) check out this paper in Physical Review Letters.

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