Tuesday, June 29, 2010

My glass of water

A glass of water sits on my desk. The glass is clear and the water is clear, therefore the boundaries between them vanish. Instead of pondering if my glass is half-full or half-empty, I'm thinking about the water. In my glass, sitting still on my desk, the water looks like such a simple thing, but it is composed of zillions of tiny molecules of two atoms of hydrogen and one of oxygen pinned together like Micky-Mouse ears.

A single molecule of water is quite dull to the non-chemist like myself. But, put together a bucketfull of these molecules and an exciting thing happens: liquidity. The molecules slosh as one, they fill the nooks and cranies of their container completely and can disolve almost anything given enough time. Along with gases, liquids are considered a fluid. Their physical properties (like density and pressure) are continuous, there are no gaps or instantaneous changes occuring thoughout their volume. Like projectiles and pendulums, fluids follow Newton's laws. Mass, energy and momentum are all still conserved but, the equations describing their motion are exceptionally complex for even the simplest case.

If I drop a stone in the center of my glass a circular ripple will move outwards, taking the information about the pebble's disturbance to the edge of the glass, where it will be reflected back. This ripple is a type of wave, and though it looks like the water is moving outwards, it isn't. Instead, each water particle moves up and down, then its neighbor moves up and down next – exactly like what happens in a stadium when the audience does the wave. If I blew on the surface of the water, I would create similar waves, except this time they would be moving in one direction instead of radially away from a point. In the ocean, you get waves created this way by the wind. The waves formed can move across entire ocean basins and crash against distant shores long after the wind that formed them has stopped blowing.

If, instead of a stone, I released a drop of dye into my completely still glass of water, a different effect would occur. The momentum of the dye dropping would take the dye down into the middle of the glass. From there it would spread out in random tendrils, the edges between the dye and the water would become blurred and ultimately I would have a homogeneous (evenly mixed) solution of dye and water. But I haven't stirred or disturbed the water in the glass, so how does the dye get evenly mixed in? It is because I keep my office well above absolute zero, so the water and dye particles in the glass all have thermal energy, and this energy causes the particles to move. At the dye-water boundary, some of the dye will move out into the water and some of the water will move into the dye, blurring this boundary. With enough time this effect, diffusion, will completely mix the dye and water.

To mix in the dye faster I could stir the water in a constant circle with a chopstick. When I pull out the chopstick, the water would continue moving in a circle, which is also called an eddy, whirlpool, or vortex. The edges would be higher than the center because of centrifugal forces, that is, each water particle, once set into motion, wants to move in a straight line until it encounters the glass edge. At the edge, there is no choice except to move in a circle. A similar effect would occur if you spun the glass, or in the case of the oceans, spun the globe beneath. The effect of the spinning earth is called the coriolis force (which isn't really a force) and creates eddies in the ocean basins that spin in different directions in the north and south hemisphere. When you flush your toilet, a whirlpool often forms, but its direction doesn't depend on the hemisphere, instead it is dependent on the conditions within the toilet itself.

Perhaps I want to mix my dye and water even faster, so I put a lid on the glass and shake it. The moving water would stretch the boundary with the dye in random directions, creating more boundary surface area allowing for faster diffusion. The sloshing water can be described as turbulent, that is, the flow interacts with itself creating an element of randomness and becomes chaotic.

What I find most interesting about water, especially in the ocean, is that all of these phenomenon can happen at the same time and at all scales. On a tiny scale there can be turbulence, on a slightly larger scale there can be eddies, larger scales still may contain waves. Ultimately we reach the scale of tides, but that is a topic for another day.

Friday, June 18, 2010

Bamboo – the grass that can be almost anything.

So what can I toss into a stir-fry, play a tune on, build scaffolding out of or put on a shirt made from? The answer is bamboo – the fastest growing member of the grass family. Right now I have several hand towels made of bamboo and a bag of bamboo shoots in the freezer. I'm debating planting some in my front yard (although it never looks healthy in neighboring yards so I might not) and flooring my house in it. Bamboo sounds like a miracle plant, but like everything it has a downside.

Wikipedia tells me that grasses can be considered the most important plant group. This group includes the grain and cereal crops people cultivate for food, wild grasses eaten by livestock or other animals, as well as bamboo, from which almost anything can be made. Bamboo shoots can be eaten, they are very tasty in a stir fry and they can be fermented into a sweet wine. Like other grasses, when bamboo is harvested it is cut, not dug up, so growing bamboo can add stability to soils and prevent erosion while producing a viable harvest.

Pesticides are not commonly used when cultivating bamboo. There are a few pests out there that like to munch on bamboo (I suppose pandas would be one), but they can be dealt with manually by cutting out the infested stems. Once the bamboo is harvested, pests become more of an issue. To prevent this, some large-scale operations treat the bamboo with a mixture that can include DDT. Dark flecks in the bamboo is often a hint that that bamboo has been treated this way. Once harvested, bamboo needs to cure. There are many ways this is done from soaking in water for months to burning techniques – it can even stored vertically and allowed to dry naturally. So, now the bamboo is ready to go.

Paper could be made through techniques mastered by the Chinese eons ago. Flutes could be made; I love the haunting sound that a bamboo flute can emit – it seems unearthly. Since I have no musical ability, I won't be making my own flute even though many websites exist to tell me how.

Bamboo fiber is becoming more and more available and is often touted as an eco-friendly option. Is it better than other fibers available? The answer is maybe; it depends how it was made. Bamboo can be made into fiber by two methods. The first, eco-friendly option is similar to how flax and hemp fiber is extracted. Stalks are crushed. Then natural enzymes take over breaking the fibers down more. Finally, the fibers can be combed out and used. The second method is essentially the same as how rayon is made from cotton. Harsh and toxic chemicals are used to break down the stalks and mechanical spinners extract the fibers. The label on my hand towels only say they are made from bamboo, not which method was used in the making of them.

If the first method is used, bamboo has a lot going for it. Like other natural fibers it is biodegradable. From the same sized space, bamboo produces ten times more fiber than cotton while requiring significantly less water. A website selling bamboo clothing says that bamboo fabric is soft (which is true of my towels), anti-fungal, anti-static and even cuts out most harmful UV rays. So, if you need a new shirt bamboo produced the right way is a great option. However, I don't recommend you throw out all your cotton shirts and replace them with bamboo - sometimes the most environmentally sensible option is to get the most wear and use out of the things you already have. But when your cotton shirts wear out, go shopping for a naturally prepared, bamboo shirt.

Wednesday, June 16, 2010

Drifting Spiders

I've been reading Rachel Carson's 'The Sea Around Us' after discovering it among my books during my recent move. My grandfather gave it to me when I first expressed interest in ocean science many years ago. The book was actually presented to him in the 50's as recognition of meteorological measurements he took as a mariner. When I first was given the book I started reading it, but didn't finish so when I found it this time I thought it was time to sit down and read the whole book.

In her chapter on island formation, this intrigued me:

So bare and desolate that not even a lichen grows on them, St Paul's Rocks would seem one of the most unpromising places in the world to look for a spider, spinning its web in arachnidan hope of snaring passing insects. Yet Darwin found spiders when he visited the Rocks in 1833, and forty years later the naturalists of H.M.S. Challenger also reported them, busy at their web-spinning.

Spiders? How did they get there? St Paul's Rocks are near the equator right in the middle of the Atlantic Ocean. Discovered by the Portuguese navy in 1511 by accident, that is by crashing into them, these islands are now part of Brazil. They jut up from the ocean floor 800 km off the coast of South America, and are made up of 15 small islands and rocks with a highest point of 17 m. This group of islands is one of the few places (Iceland is another) where the mid-ocean ridge breaks the surface. Currently, the Brazilian Navy has a science station and a lighthouse on the islands.

On the 16th of February, 1832 the H.M.S. Beagle stopped at St Paul's Rocks and Darwin had an opportunity to explore. His inventory of life included: 2 types of sea birds (boobies and noddies), a type of large crab, a fly, a parasitic tick (preying on the birds), a moth that survived by eating feathers, a beetle, a woodlouse and lots of spiders. He also observed that not a single plant or lichen could be found, since that time mosses and grasses have found their way to the island, probably helped by people.

Not including the crab, the only life form on the island that can't fly or hitch a ride is the spider. No spider can fly, even though there is an Australian spider called the flying spider. Flying spiders are tiny with pretty blue and green iridescent colouring. Their abdomens have flaps that can be extended allowing them to glide when they leap, increasing their range. But even an ability to glide wouldn't help spiders colonize remote islands.

Young spiders are forced to move away from their parents and siblings to avoid competing for food and other resources with them. To begin their journey, a spider climbs to a high point, and then point its abdomen into the air. It releases a long filament of silk that is picked up by the wind, taking the little spider up into the sky. Drifting spiders have been found thousands of meters above the remote Hawaiian Islands. Or according to Rachel Carson:

Airmen have passed through great numbers of the white, silken filaments of spiders' 'parachutes' at heights of two to three miles.

Drifting is a great way to travel as it requires no energy expenditure from the spider. I wonder how many of these drifting spiders eventually find a suitable home?

Wednesday, June 9, 2010

Sidewalks - where worms commit suicide on wet days

I walk to and from work, a round trip of 6 km or 3 km each way. It isn't a long walk, but, enough time for a little exercise and lots of thinking before I get to the office. The walk home allows me to unwind. Since I live in an urban area, the sidewalks are paved the whole way. Everyday, I see weeds poking up through cracks, worms committing suicide on rainy days, and the changing colour between wet and dry concrete.

A paved sidewalk probably wears out my shoes and knees faster, but, do sidewalks make us safer? Apparently the U.S. Department of Transportation has studied this (I'm sure other nations have looked at this as well). They found that the presence of a sidewalk, along with the speed limit, reduced the likelihood of a vehicle hitting a pedestrian by 88.2 percent – as a pedestrian, that's a big difference.

On a rainy day sidewalks look darker than when it's dry. Concrete is a matte surface, which is not shiny at all. Light is reflected diffusely off a matte surface, scattering in all directions as shown in the diagram. Dry concrete looks rather featureless and the same from all angles.

When the concrete is wet, a thin coating of water forms a smooth and glossy layer on top. A portion of the incoming light is reflected by the water layer, meaning less light reaches the concrete. The concrete now looks darker because less light reaches it to be absorbed. As an added feature, multiple reflections within this thin water layer highlights surface features in the wet concrete that can't be seen when it's dry. When the weather is frosty, a near invisible slippery film of black ice can form, which looks just like wet pavement and is a result of the same optical tricks.

Frost heave can create cracks in the concrete as can roots of nearby trees. I suspect small earthquakes could also form cracks. Once there is a crack, plants move in and take advantage of this new growing space. Ultimately they widen the cracks and more plants move in, creating a cycle that can destroy a sidewalk. Where I live dandelions and chamomile seem to thrive in these cracky environments.

So, why do so many worms commit suicide on sidewalks? When it rains, the worms' underground home fills with water. Since worms breathe through their skins, to avoid drowning they come up to the surface. Once in the air they can breath again. If they wander about and end up on the sidewalk they may not find their way back into the ground again, ultimately drying up when the sun comes out or forming a robin's lunch. Good for the robin I guess.