High-Speed Snowboarding Trains

By Roland Piquepaille

This seems as a far-fetched idea, but scientists from the City University of New York think that "superfast trains of the future could glide over fluffy tracks like snowboarders over snow," according to "Trains get fluffy," an article published by Nature. They compared the lift forces experienced by red cell blood cells moving through our veins to the ones produced in snowboarding by skiers. And they concluded that the forces in presence were similar, and could be applied to high-speed trains. As long as you go fast enough, even a train can run on feathers, adds PhysicsWeb. The researchers think the future fluffy tracks, capable to support 50-ton trains, could be built by using goose feathers, like the ones found in pillows. So far, they don't have a prototype for the tracks, but they already bought the pillows. Read more...

Let's start with Nature.

In snow, this lift is created by air between the tiny ice crystals. When the snow is compressed by the weight of a board, the air is pushed out from the porous snow, exerting an upwards pressure on the board. This cushion of air means that there is very little friction slowing the snowboarder's motion.

The same forces allow red blood cells to glide smoothly along our capillaries. A loose mesh of sugar-coated proteins on the vessel walls gets squeezed by the passage of a red blood cell, pushing out fluid from between the protein strands.

But why applying red cells blood and snowboarders' behaviors to a high-speed train?

To find out whether the forces generated would be enough to support a whole train, team leader Sheldon Weinbaum, of the City University of New York, and his colleagues measured the lift force created when snow inside a cylinder is compressed by a piston.

During the first one and a half seconds or so of squeezing, there was a surge in upwards pressure as air was pushed out of the porous snow. Within a couple of seconds, this pressure dropped virtually to zero, as most of the air had drained away. This is why light, fluffy snow can support the heavy load of a snowboarder, provided that she doesn't linger for longer than about a second.

It's time to turn to PhysicsWeb for more technical details.

To measure the pressures that develop during snowboarding, Weinbaum and colleagues used a piston cylinder apparatus that was capable of reproducing the dynamic forces experienced by a moving snowboard. They calculated that the air trapped in the snow can easily support the weight of a 70-kg snowboarder. They also found that the pore pressure underneath a snowboard with a surface area of 5000 square centimetres is about 1.4 kilopascals.

Extrapolating these results to the case of a 50-ton high-speed train, Weinbaum and co-workers calculated that 9.8 kilopascals of pore pressure would be needed to support a train that was 25 metres long and 2 metres wide. According to the scientists, a porous material with a permeability of 10^-8 metres squared or smaller -- such as goose down -- could be used as a track that was capable of supporting the weight of the moving train.

You'll find additional diagrams in the PhysicsWeb article. But the conclusion belongs to Nature.

The track would consist of two side walls, filled by fluffy material with the same bouncy properties as goose down. Goose down itself would be too costly for filling miles of track; but there are plenty of synthetic substitutes, like those used to fill cheap pillows.

Because the train would only be supported when travelling at high speed, so Weinbaum and colleagues suggest that the vehicles should have retractable wheels that run along the track side walls when the train slows down or as it gathers speed from a standing start.

Will we ever see such trains? As the researchers admit,  "It's a far-out idea." But they do have the pillows.

For more information, the research work has been published by Physical Review Letters under the title "From Red Cells to Snowboarding: A New Concept for a Train Track." Here is a link to the abstract.

Sources: Philip Ball, Nature, November 10, 2004; Belle Dumé, PhysicsWeb, November 10, 2004

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