Just as powdery snow supports a slaloming snowboarder, a material as fluffy as goose down may be able to support a speeding train, a team of biomedical engineers has calculated.
Sheldon Weinbaum of City College of New York and colleagues arrived at this provocative idea from studying blood flow. Blood vessels are lined with a compressible gel, and red blood cells glide over it by surfing the liquid trapped in the gel. In the same way, the scientists calculated, a sliding snowboarder rides the air trapped in fresh snow and not the snow itself. They squeezed snow in a piston and found that it held air long enough to support a snowboarder moving at 10 meters per second, they report in the 5 November Physical Review Letters.
The scientists then tried squeezing goose down. It didn't hold air as well as snow did, but it still sustained a sizable pressure surge for a couple tenths of a second. Scaling up from the data, the researchers argue that when spread in a channel with airtight sides, a material like goose down could support a 25-meter-long, 50-metric-ton train car moving at least 70 kilometers per hour. Weinbaum hopes to build a working scale model of the tobogganing tram.
"It's surprising that such great loads can be supported by just air and a porous medium," says Timothy Pedley, a fluid dynamicist at the University of Cambridge in the United Kingdom. But spiriting trains along fluffy byways is so far just a wild idea.
CREDIT: PHOTOS.COM |
