19 Feb 2017

Living or Non-Living, There Is No Once-Living

As educators, we pay close attention to common misconceptions of our students and readers, and are prepared to correct them. Being human, we ourselves are equally susceptible to misconceptions and errors of logic. This particular one has popped up from more than one source, so I’m going to explain it here.

Readability is very important to educators, and particularly to children’s writers. We try to use vocabulary that students won't get stuck on, preventing them from concentrating on the concepts that are being explained. For this reason, we often use categories of living and non-living when describing the biotic/abiotic dichotomy in science. Biotic means living, and abiotic means non-living.

However, this language sometimes leads into a misconception of associating living with the state of being alive. Dead stuff is still biotic, or living if we’re using simplified language. Lacking signs of life does not make something abiotic. (Texting teenagers, for example, may not appear alive but still remain classified as biotic.)

This becomes less problematic if we apply the categories to groups, rather than to individuals. Lumber doesn’t resemble a tree, but it is still biotic. Trees are biotic components of the world. Similarly, an infertile individual does not get classified as non-living (abiotic). They are classified along with their whole species, as biotic.

Neither is there is a third, “once-living” category—no “once-biotic.” Sedimentary rocks were formed from the remains of living things millions of years ago. In that sense, the components of rocks were once living, but rocks are classified as non-living.

Biotic: things that reproduce, grow, and die, and the waste from these things
  • plants
  • animals
  • microorganisms
Abiotic: not derived from biotic things

  • air
  • water
  • sunlight
  • rocks
  • etc.

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Photo via US Dept Agriculture, used under CC BY-2.0 license.

10 Feb 2017

Surprisingly Slippery Science

Canada is a land of ice skating.  The longest skating trail in the world (according the Guinness World Records) is a 30 km trail around Lake Windemere in BC. Both our Women's and Men's Hockey teams have the best records in the world. Canadian figure skaters are an international powerhouse. So we really should know how a skate works. But do we?

Many of us have been taught that skates put pressure on the ice, which causes the ice to melt, and the skate then glides on a cushion of water.

It's certainly true that pressure decreases the melting point of ice. The pictures below show this. They're screen captures from an experiment shown in the National Geographic video at

 http://video.nationalgeographic.com/video/i-didnt-know-that/idkt-ice-skating-science
 


Scientists place a wire with weights attached on top of a block of ice. Weights on the thin wire exert a lot of pressure on the ice.


The pressure melts the ice and the wire cuts through the block. The ice re-freezes above the wire as the pressure is released.

But there's a problem. The pressure of a skater is only enough to increase the melting point of ice by less than 1 degree. So how do skates work at -20 degrees?

A second explanation often offered is that the friction of the skate moving across the ice generates enough heat to melt the ice, and that creates the water for the skate to glide on. But that can't be the only explanation.



We've all had the experience of finding out that ice is slippery even when you're standing still. There's no need for friction to melt the ice to make it slippery.

The third answer was known by Michael Faraday as long ago as 1850, but somehow his views were largely ignored. There is always a layer of water on the surface of the ice. That's why two blocks will freeze together if you join them. The water layer occurs because the structure of the ice breaks down at the surface. The thickness of the water layer increases with the temperature of the ice.
Surface of Ice - from Wikimedia Commons


So pressure and friction make a small difference, but essentially skates slide on a layer of water that is always on the surface of the ice.

SkateTechnology

The technology of skates has changed a lot over the ages.

Steven G. Johnson (creative commons licence)
This picture is of medieval bone skates on display at the Museum of London. The accompanying label quoted a 12-century description of skating in London by William FitzStephen (Londoners would "fit to their feet the shinbones of cattle" and propel themselves with an iron-tipped stick).

This is an illustration of modern speed skating "clap skates". In my book Faster, Higher, Smarter you can find out how clap skates work and read the story of how this clever invention took a hundred years to become mainstream in speed skating.