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Physicists Manipulate Waves To Make Tractor Beam

Scientists studying how floating particles move on the surface of water have come up with a way to pull them in, push them away or make them stay still. They can now precisely control objects by generating waves with specified frequency and amplitude.

The work by Australian National University researchers might find use in cleaning up oil spills. It could also lead to a better understanding of how moving water develops into rip currents.

"We have figured out a way of creating waves that can force a floating object to move against the direction of the wave," said physicist Horst Punzmann, who led the research. "No one could have guessed this result."

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What Some Can Do With A Little Tension

These striking images of an insect that walks on the surface of water come from the lab of John Bush, an MIT applied mathematics professor. Bush studies fluid dynamics, focusing his science—and the art that often comes from it—on surface tension.

Visualized in the pictures above is the movement of the water strider, a bug that, according to Bush, stands on water through “surface tension force generated by curvature of the free surface.” It propels itself across the surface by rowing hydrophobic legs, which transfer momentum to the water by deforming the film-like surface and shedding fluid vortices as seen in these pictures. Click here to see a larger version of the top picture, which graced the cover of the journal Nature several years ago. Read the paper that describes the physics of water strider motion here.

The lab showed the vortices by floating Thymol Blue, a dye that is insoluble in water and is often used as a pH indicator, on the water’s surface.

We’ve featured work from the Bush lab before. Check out this story to see how you can play with surface tension to make fun cocktail boats driven by alcohol.

All images courtesy David Hu, Brian Chan & John Bush/MIT.

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Predicting Where Water Will Go In A Hurricane

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by Joel N. Shurkin, Inside Science

In most hurricanes the greatest damage is done not by the wind but from the storm surge, the mountain of water pushed by raging winds from the ocean to deluge the land.

There is always a level of unpredictability when dealing with Mother Nature, but knowing where the water would go when a storm is bearing down on the coast would be useful, particularly in densely populated coastal cities such as New York, which maintains complex systems of houses, office buildings, sidewalks, basements, alleys, subway stations, and streets clogged with parked cars.

Scientists at the College of William & Mary’s Virginia Institute of Marine Sciences at Gloucester Point, Va., reported they have a computer model that may do that, starting about 30 hours before the storm comes ashore. At least it worked in retrospect with the Hurricane Sandy, which devastated the East Coast in 2012.

Click through for an interactive map of New York City flooding and a video.

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The Science Of Ice

Ever wonder what makes ice slippery? As it turns out, the answer is more complex than this simple question lets on. It has to do with the unique attributes of water molecules and nearly frictionless movement over ice.

There is a lot of slipping and sliding now in the spotlight because of the skating, skiing and curling going on at the 2014 Winter Olympics. That’s why the National Science Foundation and NBC Learn put together a video primer on the science of ice.

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