Sock Physics - Experiments with Static Electricity

Zap!  Pull your clothes from the dryer and unless you've used one of those funny smelling anti-static papers you just might get a shock of electricity.   When the clothes tumble in the dryer and the water is removed, electrons are removed from their bonding atoms and static charges build on the clothing the same way walking across a rug on a dry day builds charge which is then released with a zap when you touch a conducting surface, like a door knob.  Zap!

When I tossed my clothes into a pile for sorting, I  watched as a loose strand from one sock reached upward as to defy gravity but stayed tethered to the sock.   Even knowing why this is so (or at least one explanation) it fascinates.  Over the next few minutes I held off sorting the clothes and took a few photographs.

Fig 1: Back lit sock with strand balanced against gravity by the repulsive force of static electricity

Even more amazing (to me), was the fine structure in the hair-like appendages that stood in repulsion to the main strand due to the repulsive forces of like charges.  When electrons are removed from neutrally charged atoms, a net positive charge remains.  The force between like charges is a repulsive one so the individual strands are forced apart.

Fig 2: fine structure detail from Fig 1 showing small fibers of the sock in mutual repulsion.

A few minutes later, the long strand was clearly losing the battle against gravity as the collected charges slowly dissipated as nitrogen and oxygen molecules took them away.   

Fig 3: Strand 5 minutes later

Eventually, the rebellious strand lost its charge and rejoined the sock.  

Fig 4:  Composite showing positions of strand over 5 minutes as it loses charge and settles under the force of gravity

Fig 5: Mouse-click for animation 

All Aboard II

All Aboard II, a set on Flickr.

West Oakland's 16th Train Station was closed following Loma Prieta in 1989. The local train service has been relocated, but the 16th Street Train Station is gaining a new life as a center for community activities and special performances.

For more information, see http://www.indiegogo.com/16thStreetStation

Wildcat Creek in Time Lapse

Wildcat Creek did not run dry this year and still has a respectable flow. As I watched some leaves floating slowly by, I thought ahead when heavy rains will fill the creek above the rocks I was standing on. I also wondered how fast the leaves would be moving with the increased flow. One way to visualize this would be to take a time-lapse sequence!

Using the iPad I shot two sequences of 200 frames each. The first sequence was shot at 10 fps and the second at 1 fps. The two sequences were combined into a 40 second video using iMovie for the iPad and a soundtrack was added from a recording made a few years ago using a Sony MD Walkman. The first 20 seconds of the video shows the flow at normal speed and the second 20 seconds shows the flow at approximately 10 times normal speed. When the rains come, I can take a standard sequence and compare them. Perhaps not the most direct way to determine the comparative speed of flow in a creek, but it offers an alternative approach.

di Rosa Art Preserve

di Rosa Art Preserve, a set on Flickr.

Located near Napa, the di Rosa Art Preserve is 200 acres of the selected works of Northern California artists and includes metal work, ceramics, photography, paintings, and other categories that I cannot identify (e.g., 50's vintage cars adorned with a collage of collected items).  For more information and tours see http://www.dirosaart.org/.