Taxed roads
Question: What causes the corrugations in dirt or sand roads after they have
been used by vehicles for several weeks? Why do the corrugations occur with the
same frequency despite differences in vehicle tyres and wheel diameters?
(continued)
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Answer: Further to the answers already given, there is a similar phenomenon
with railway tracks. These degenerate over time into 鈥渞oaring rails鈥�, well-known
on British railways and here in Toronto on our streetcar system. The cure is to
grind the rails back to smoothness.
The exact process in the case of railways is unknown, but is it in fact the
same effect of inherent resonance of the material?
Philip Webb
University of Toronto, Canada
Eh?
Question: Is it true of all natural languages that the most frequently used
words are shorter than those used less frequently?
(continued)
Answer: My boyfriend completed a thesis 20 years ago on Zipf鈥檚 Law, in which
he measured the lengths of similar hieroglyphics from ancient Egypt. The
research was not published, and the results are now somewhere in a drawer. He
found that in written or carved languages, some forms of common words became
substantially shorter over hundreds of years鈥攎uch, I imagine, as they
would have before the advent of computers. The rise of standardised printing
using computers will mean that words and founts remain substantially unchanged,
but you can already see the @ symbol and other forms of shorthand that people
use in e-mail.
A. Ross
by e-mail, no address supplied
No flakes
Question: How does antidandruff shampoo work?
Answer: Dandruff is thought to be caused by overgrowth of yeasts such as
Pityrosporum ovale which live on normal skin. This overgrowth causes local
irritation resulting in hyperproliferation of the cells (keratinocytes) forming
the outer layer of the skin. These form scales which accumulate and are shed as
dandruff flakes.
Antidandruff shampoos work by three mechanisms. Ingredients such as coal tar
are antikeratostatic and they inhibit keratinocyte cell division. Detergents in
the shampoo are keratolytic鈥攖hey break up accumulation of scale. Finally,
antifungal agents such as ketoconazole inhibit growth of the yeast itself. Other
components such as selenium sulphide also inhibit yeast growth and therefore
scaling.
Roddie McKenzie
University of Edinburgh
A lie-in
Question: What physiological or psychological mechanism stops adult sleepers
falling out of bed?
(continued)
Answer: Years ago I recorded the head rotation of a few adults asleep. They
were lying on a very wide surface without any covering to give them any
unconscious clue where they were during sleep. Their heads turned to the right,
the left and then lying on their backs and so on irregularly during sleep, but
they never slept nose down.
Therefore they could not fall out of bed unless they had gone to sleep with
their backs right at the edge of the bed, or the bed was extremely narrow and
had no bedding to keep them in.
I have also observed children sleeping. Below the edge of five they did
indeed turn nose down from time to time, thus being able to turn right over and
fall out of bed. It seems that what the child learns is not to turn nose down,
probably because of the learned fear of suffocating.
John Forrester
Edinburgh
Nuke 鈥檈m
Question: It has been suggested that intercontinental ballistic missiles with
nuclear warheads could be used to destroy or deflect comets or asteroids on a
collision course with Earth.
For a comet with velocity and size of Hale-Bopp, how much energy would it
take (in kilotonnes) and how far from Earth would the missile have to
intercept the intruder in order to respectively destroy or deflect it? And our
missiles fast and manoeuvrable enough?
Answer: It would be unwise to use nuclear missiles to destroy an asteroid, as
it would only slightly reduce the problem. This is because instead of one big
lump on a collision course with Earth, we would have millions of tonnes of
radioactive dust and rubble, which on reaching the atmosphere would produce a
鈥渘uclear winter鈥� by blocking out sunlight.
As to how much energy is needed to deflect the asteroid, a simple answer is
that you would need less energy the farther away the asteroid was. Gravitational
systems are prone to an effect from chaos theory whereby small changes in
starting conditions greatly effect eventual outcomes (the infamous butterfly
effect), so a small deflection of the rock鈥檚 course at a great distance will
produce a huge change by the time it would otherwise have hit us, and it would
sail by.
Current estimates say we could easily deflect an asteroid if we spotted its
collision course 10 years in advance. Sadly, our current detection systems
wouldn鈥檛 spot it until it was about a year away, so it would need a larger blast
to deflect it.
Maxwell
by e-mail, no address supplied
Myopic mammals
Question: I would estimate that about 40 per cent of the people whom I know
need glasses or contact lenses for distance vision. Assuming that this sample is
typical of the human race, I would like to know why it is that eye problems
prevalent in humans such as myopia (short-sightedness) seem very rare in wild
animals?
As far as I know, myopia is a genetic condition and so is not usually
acquired by habits such as reading small print (otherwise one would expect
recovery after stopping the habit). Obviously, it is not easy to test the
eyesight of an animal, but if the incidence of myopia is as high in wild animals
as it is in humans, then how can animals survive?
(continued)
Answer: Any doubts I had that myopia was induced by reading were dispelled at
the 1993 conference of the American Society for Limnology and Oceanography in
Edmonton, Canada. As I queued for the barbecue I was shocked to notice that
every one of the 50 or so people ahead of me was wearing glasses (I also wear
glasses). Assuming nobody was wearing reading glasses, and that the 40 per cent
estimate of myopia is correct, the chance of selecting a such a sample of 50
myopics at random is 1.3 脳 10-20.
Simon Wright
Hobart, Tasmania
This week鈥檚 question
Concentration: People doing a tricky job will stick their tongue out and
clamp it between their lips. Why? Does it apply to all cultures?
Steve Townsend
by e-mail, no address supplied