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A video of the cylinder-levitation experiment.

You spin me ’round: a cylinder hovers next to a greased belt moving at just the right speed. Credit: M. P. Dalwadi et al./J. Fluid Mech.

Fluid dynamics

How does a cylinder levitate? Scientists explain the maths behind the magic

A model shows how a spinning cylinder can stay suspended in the air next to an oil-slicked moving belt.

An oil-coated belt run like a vertical treadmill can levitate a cylinder held next to it. Now researchers have developed a mathematical model to explain this goopy form of anti-gravity.

Previous research showed that a cylinder placed against the side of a moving belt covered in oil and then released will start to rotate, get coated in the fluid and, at the right belt speed, stay suspended against the belt. But the model devised to explain the phenomenon had some gaps.

Mohit Dalwadi at the University of Oxford, UK, and his colleagues have fleshed out the details. The group experimented with cylinders of various masses and sizes to find the belt speed needed to levitate each object. The model that the team developed takes into account how the oil from the cylinder comes together with oil from the belt — and shows that pressures near that joining point support the cylinder against gravity.

More Research Highlights...

Camera-trap image of Dendrohyrax interfluvialis

Some tree hyraxes scream in the night, but the newly identified Dendrohyrax interfluvialis (above, camera-trap image) utters a complex series of squawks, rattles and barks. Credit: J. F. Oates et al./Zool. J. Linn. Soc.

Zoology

A bark in the dark reveals a hidden hyrax

Its neighbours scream, but a new species of tree hyrax — a cousin of the elephant — unleashes a rattling bark.
Plastic and other debris floats underwater in blue water

Plastic detritus from snacks and meals floats in the Red Sea. Marine sampling shows that food waste accounts for nearly 90% of plastic pollution at some locales. Credit: Andrey Nekrasov/Barcroft Media/Getty

Ocean sciences

Humanity’s fast-food habit is filling the ocean with plastic

Food bags, drink bottles and similar items account for the biggest share of plastic waste near the shore.
Conceptual artwork of a pair of entangled quantum particles.

An artist’s impression of ‘entangled’ particles, which share properties even at a distance. Entangled photons can be used to help secure a multi-party video meeting. Credit: Mark Garlick/Science Photo Library

Quantum information

Quantum keys dial up tamper-proof conference calls

A new experiment efficiently distributes the highly secure keys to four parties instead of the typical two.
Farmers harvest pineapples in a field.

Workers harvest pineapples in Lingao County, China. Less than one-third of the money spent on food eaten at home reaches farmers. Credit: Yuan Chen/VCG/Getty

Economics

Poor harvest: farmers earn a pitiful fraction of the money spent on food

The bulk of consumer food spending around the world ends up in the coffers of distributors, processors and other parties beyond the farm gate.
A woman wearing a protective face mask splashes her hands in a jet of water

A pedestrian seeks relief from searing temperatures in Spain, where a high proportion of heat-related deaths have been linked to climate change. Credit: SALAS/EPA-EFE/Shutterstock

Climate change

More than one-third of heat deaths blamed on climate change

Warming resulting from human activities accounts for a high percentage of heat-related deaths, especially in southern Asia and South America.
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