NPR : News

Filed Under:

What Does Sound Look Like?

When light passes between areas of different air density, it bends. You've probably noticed the way distant pavement seems to shimmer on a hot day, or the way stars appear to twinkle. You're seeing light that has been distorted as it passes through varying air densities, which are in turn created by varying temperatures and pressures.

In the mid-19th century, German physicist August Toepler invented a photography technique called Schlieren Flow Visualization to visually capture these changes in density. The setup is a bit hard to explain in words (watch the video above for a full explanation) but it allows scientists and engineers to see things that are normally invisible: the rising heat from a candle, the turbulence around an airplane wing, the plume of a sneeze.

It can also be used to see sound. Sound, after all, is just another change in air density — a traveling compression wave. A speaker pushes on the surrounding air, creating a wave that travels outward until it encounters the ear drum.

As a result, Schlieren Flow Visualization can be used to see sound as well. Sound waves travel extremely fast (761.2 miles per hour) so a high-speed camera is needed to see the waves' passage.

Michael Hargather, a professor of mechanical engineering at New Mexico Tech, uses just this approach to study the shock wave caused by explosives. He's made Schlieren videos of everything from firecrackers to car bombs, but he's also filmed more benign shock waves — a book landing on a table, the end of a towel being snapped, and a man clapping. You can see them all in the video.

Copyright 2014 NPR. To see more, visit http://www.npr.org/.

NPR

'It's A Surviving Tool': 'Native' Tells Satirical Stories Of Life In Israel

NPR's Kelly McEvers talks to author Sayed Kashua, an Israeli-Palestinian whose satirical weekly columns in Haaretz newspaper are collected in his new book called Native.
NPR

What The Heck Is Natural Wine? Here's A Taste

Natural wines can be off-putting at first: perhaps darker than usual, a little fizzy or cloudy. Some find them charming, others unsophisticated. Here's a guide to this trending, quirky style of wine.
NPR

#MemeoftheWeek: What Would Honest Abe Really Think Of Politics Today?

#ThingsLincolnDidntSay brought the 16th president back to Twitter on his birthday to weigh in on the current presidential race. But in reality, he might actually feel at home.
NPR

Colonialism Comment Puts Facebook Under Scrutiny

A Facebook board member lambasted a decision by regulators in India, the social network's second-largest market. He thereby sparked new scrutiny of Facebook's intentions in that country.

Leave a Comment

Help keep the conversation civil. Please refer to our Terms of Use and Code of Conduct before posting your comments.