Flying Circus of Physics newsletter for Nov 2014 - Jan 2015
Data pubblicazione: 5-nov-2014
First, a few words about the web site at www.flyingcircusofphysics.com
The site now has over 400 stories, and four more are added every month.
The index has been greatly expanded to include not only individual items but also collections of related items. Here are a few of the collections:
- Accidents
- Animals
- Bathroom, physics to do in a
- Breakfast, physics to do at
- Cars
- Closet, physics to do in a
- First date, physics to do on a
- Food
- Garden
- History
- Ice
- Illusions
- Kitchen, physics to do in a
- Magic tricks
- Patterns
- Pizzas
- Pub physics
- Rubber bands
- Shadows
- Sports
- Stunts
- Vortex
The site has several thousand video links, and the number of journal citations exceeds 12 000.
If you have ideas for new stories or new index collections, please let me know.
Flying Circus of Physics newsletter for Nov 2014 - Jan 2015
Surges
The sudden onrush or release of materials is the subject of research in all the sciences and engineering fields, even social engineering. Often you might not notice a surge, such as a surge of cold air, but some surges can be so threatening that they are riveting. Here I have sorted out a few of my favorite examples of surges in three main types: water, electric, and people.
Water surges
Freeway geyser
http://www.youtube.com/watch?v=4BkFp5CL4q0&feature=related
We can guess that the geyser was caused by a sudden rain downpour elsewhere in the city and that so much water has run downhill through the drainage pipe that it erupts from a vertical shaft in the freeway, blowing the huge manhole cover off and into the traffic lanes. But if that is the explanation, then why do we see a second geyser? (There could have been even more.)
Civil engineers who study such geysers can explain the repeat performances. The water flows through the drainage pipe, rapidly filling a temporary storage area at the low end. As more water flows toward that area, a surge front of high pressure in the water moves up the pipe. When the surge front reaches a vertical shaft, it pushes water up the shaft so rapidly that the water gushes from the shaft, as we see in the video. That upward motion relieves the water pressure down in the pipe but within seconds, the column of water still in the shaft slumps, sending a high pressure wave back down the pipe toward the storage area. The wave reflects from the lower end, and when it returns to the vertical shaft, another geyser shoots out of the shaft.
Japan tsunami
http://www.youtube.com/watch?v=noq8FYvRqgs
Soon after the earthquake that hit Japan in 2011, a huge wave was sent rushing toward the shore. This terrifying footage shows the complete lack of respect that the surge of water had on the cars, buildings, and people caught in its path. Tsunamis are studied by a wide range of people, from oceanographers to architects to politicians.
Electric surges
Fireball traveling along power lines
A surge of current through the power lines produced electric arcing between two lines. The large electric field ionized air molecules, which then gave off light when they regained electrons. The arcing also heated the air, which caused the arcing to migrate along the wires. The bright flash that you see at the end of the video was due to a transformer exploding when the arcing reached it.
Surge of electric demand: England switches on tea kettles at the end of The East Enders television show
http://www.wimp.com/britskettles/
People surges
Many scientists and engineers study the traffic behavior of people in every situation from walking across a campus to forming organized movements into or out of stadiums. However, the most important situations involve an uncontrolled surge of people, such at the 1979 concert by The Who in Cincinnati, Ohio, here in the U.S. Most of the seats in the stadium were unassigned, which meant that a ticket holder needed to rush into the stadium as soon as the entrance gates were opened in order to get a good seat. Before anyone was admitted and with those gates still closed, The Who began a sound check. Many people in the crowds at the gates apparently thought that the music meant the concert had begun and so they surged forward, compressing people in front of them. In those awful few moments, 11 people were killed and 26 hurt.
Simulations
Here is an example of modern computer simulations of dense crowd flows:
http://www.youtube.com/watch?v=pqBSNAOsMDc
Engineers and architects attempt to use such modeling to design safer entrances and exits for crowds in sporting and religious gatherings, especially when there is a possibility of a panic exiting.
Football audience surging (Turn down your volume to avoid the loud heavy metal background music.)
http://www.youtube.com/watch?v=kJiBg9Y3P8A
Although the danger of surges in sporting audiences is widely known, such surges continue to occur almost yearly. The excitement is so great that the sports fans ignore the strong chance that someone down at the field barrier will be crushed.
Black Friday store surge
https://www.youtube.com/watch?v=DigiWS1YhxI
Black Friday is the name given to the day after Thanksgiving Day in the U.S. On that day, a store will offer big discounts to lure in customers so that the profits are in the black (successful) instead of the red (not successful). However, as the video shows, a black-Friday surge of people into a store can be dangerous. This last video gives a hint of that danger. No one was killed or seriously hurt but they could have been.
https://www.youtube.com/watch?v=YOVD-m8urJU
There are countless other examples of surges. As a general rule, you don’t want to be in one.
Physics is everywhere, even in a black-Friday shopper surge.
Cheers,
Jearl Walker