Posts Tagged ‘vibration’

It’s getting kind of hectic

Those tremors you feel in your high-rise building may not be an earthquake.  Ten minutes of violent shaking in a 39-story Seoul skyscraper were attributed in 2011 to “17 middle-aged people” doing Tae Bo to “The Power” by early 1990s German hitmakers Snap!

Every building has its own natural resonances that can be excited by rhythmic activity.  In most buildings these resonances are relatively docile and hard to excite, but when wide structural spans and thin slabs lead to a low natural frequency, it doesn’t take many kickboxers to get things…kind of hectic.

Sight of sound

Your eardrum converts the motion of the air into something you can hear, but what if everything around you could work the same way? In a recent TED Talk, MIT researcher Abe Davis demonstrates cutting edge research into extracting audio from silent video of everyday objects exposed to sound. Using high-speed video equipment and even a consumer-level camera, he extracts intelligible music and speech just by watching a nearby houseplant or a snack bag—the proverbial “fly on the wall”. Acknowledging the surveillance possibilities (which were already feasible using lasers), the research pushes beyond audio to expose the natural modal movement of an object by simply ensonifying it and recording what happens, allowing one to push, pull, and shake something virtually without ever touching it.

Did you hear that meteor?

This past weekend, the Perseid meteor shower reached its peak overnight between Sunday and Monday.  With a little patience and clear skies, the electromagnetic radiation in the visible spectrum that meteors release is easily seen.  But did you know that meteors also release very low frequency radio waves, below 30 kilohertz? According to livescience, going back hundreds if not thousands of years, people have claimed to hear sounds of meteors as they raced across the sky.  The very low frequency radio waves travel at the speed of light (not at the speed of sound) and arrive at the same time observers see a meteor passing overhead.  However, the radio waves need a transducer to could create a sound that is audible to people. This phenomenon is known as electrophonics, and in order to study it further, physicist Colin Keay created sounds in ordinary objects by exposing them to very low frequency radiation in a laboratory. Lightweight, membrane-like objects such as aluminum foil, foliage, thin wires, even dry frizzy hair produced sounds that were easily heard.

2012 Geminid Meteor Over Texas

Never having heard this before, we thought we would head out to Long Island to try and hear it for ourselves. We saw and heard a few things…First, there are quite a few sky-watchers in New York, which unfortunately meant that second, people noise and car stereos are louder than the sound from meteors.  Also, being by the beach, the sound of the ocean waves were also louder than the meteors.  Even if we couldn’t hear them this time, and although there were a few passing clouds, meteor showers still create a wondrous sight.  We will just have to make plans to go somewhere a bit quieter next time.

 

Frozen spring

One of the things one learns studying acoustics (and many other physics topics) is that the behavior of a complicated physical system can often be simplified into an analogy of masses and springs.  The gobs of air that surround us have elasticity and they have mass, and these are the properties that allow waves to travel through the air as sound.

Perhaps a more intuitive example of a spring-mass system can be found in any toy store: the classic Slinky.  The familiar coil toy can be used to demonstrate lots of different wave phenomena (longitudinal waves, transverse waves, standing waves), and when that gets boring, it is more commonly used to demonstrate walking down stairs.

We recently came across this high-speed video of the very interesting spring-mass behavior of an extended Slinky at rest, dropped from height, in which the bottom end of the Slinky seems frozen in mid-air.  There are excellent technical explanations of what is going on out there (and probably on a tricky physics midterm or two), but suffice it to say that it all goes back to the interplay between mass and elasticity as the Slinky simultaneously contracts and falls.

[Via kottke.org, @jenvalentino]

See the unseen

To promote their new vibration analyzer, measurement instrumentation company Fluke commissioned some amazing high-speed video of—you guessed it—things vibrating!  Putting the fascinating physics of vibrating plates and cylinders aside, you will have to admit that it’s interesting how a cymbal deforms at 1,000 frames per second.  (And if that doesn’t do it for you, the shaking basset hound at the end is pretty nice too!)