Beeline
Question: My girlfriend tells me it is impossible to explain how the
bumblebee flies. Apparently it defies the laws of physics. Is this true?
Answer: The infamous case of the flightless bumblebee is a classic example of
carelessness with approximations.
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It stems from someone trying to apply a basic equation from aeronautics to
the flight of the bee. The equation relates the thrust required for an object to
fly to its mass and the surface area of its wings. In the case of the bee, this
gives an extremely high value鈥攁 rate of work impossible for such a small
animal. So the equation apparently 鈥減roves鈥� bees cannot fly.
However, the equation assumes stationary rather than flapping wings, making
its use in this case misleading.
Of course if equations fail in physics there is always empirical
observation鈥攊f a bee looks as if it is flying, it most probably is.
Simon Scarle
London
A full explanation of how bumblebees and other insects fly can be found
in 鈥淥n a wing and a vortex鈥� (New 杏吧原创, 11 October, p 24)鈥擡d
Glass menagerie
Question: I have just seen a film on television showing a variety of
beautiful translucent deep-sea creatures, including a squid that was completely
translucent except for its eyes and ink gland.
Why are these creatures translucent, how is this achieved and, in the event
that a gene for translucency exists, would it be possible (if not desirable) to
make humans translucent?
Answer: Several multicellular organisms are almost completely transparent,
and many possess at least some translucent body parts or tissues. The most
striking animal examples include some deep-sea squids and the amphipod
Phronima, several species of marine and freshwater shrimps, practically all
100 or so species of arrowworms (chaetognaths), the wings of some butterflies
(Callitaera menander), the predacious aquatic larvae of the insect
Chaoborus and even some species of fish, such as the catfish
Kryptopterus.
Obviously, being transparent makes visual recognition by both predators and
prey more difficult.
In marine animals, transparency permits vertical migrations across water
layers of differing hues and light intensities, without the animal having to
worry about adjusting body colour. Even mammals possess transparent tissues such
as fingernails and the lens of the eye.
A South Atlantic transparent medusa I picked up in 1967 was so perfectly
transparent and biconvex that, by shining sunlight through it like a hand lens,
I was able to light a cigarette with it.
Transparent tissues share some general features: no blood vessels or very
few, an absence of pigment cells, extracellular spaces that are smaller than the
wavelength of light, and a relatively regular and repetitive structural unit.
Commonly mucopolysaccharides and collagen are involved in animal transparency,
but glycoproteins (in jellyfish) and chitin (in insects) may also be found.
Some tissues are impossible to make translucent: nerves will always look
white even in transparent organisms because of their high lipid content, and the
retina has to remain pigmented because of its visual purple (rhodopsin).
Obviously, stomach contents cannot be made invisible.
The maintenance of transparency requires energy. Dead tissues eventually lose
their transparency, a process that is accelerated by heat鈥攍ook at the
lenses of boiled fish eyes). This explains why the 鈥渋nvisible man鈥� of TV fame
was never shown drinking a glass of wine.
V. Meyer-Rochow
Oulu, Finland
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?
Answer: Nearly all matter has an in-built natural resonance, including the
grains of sand and gravel which normally make up the surface of a dirt road. In
response to the movement and vibration of the road surface material, which is
generally caused by any kind of traffic movement, whether on tyres or not, the
grains of sand form a sinusoidal pattern related to the natural resonant
frequency of the dominant material. The pattern manifests itself as ridges or
corrugations on the road surface. It is independent of the tyre or wheel size,
and the corrugations are all generally uniform for a type of material.
This is a natural phenomenon, and even if a road is graded and levelled
regularly, the corrugations will inevitably appear. The greater the traffic
movement and hence vibration, the quicker the ridges will appear. Fine, sandy
material will not form ridges very easily, but the coarser the material, the
more severe the corrugation will be鈥攁s is easily proved here in Oman, a
land of corrugated roads.
David Fryer
Muscat, Oman
Answer: The dirt particles making up the surface of the road behave in a
similar manner to water molecules in the sea. Vehicles travelling along the road
have the same effect as wind over water, ruffling up waves perpendicular to the
direction of travel. The corrugations move along the road slowly like waves, but
the effect is confused by the fact that vehicles travel in both directions.
Helen Payne
Weinheim, Germany
This week鈥檚 questions
Box of tricks: On a recent visit to Edinburgh, we were in a pub which had an
instrument at the end of the bar approximately 30 centimetres in length and 3
centimetres wide. It appeared to be a black rectangular box, open on one side,
with a series of red lights inside. When you moved your head swiftly, a brand
name of vodka appeared to flash along the surface of the bar although not all
the letters could necessarily be seen at once. How did the box produce this
image, why could all letters not be seen simultaneously and why was the image
only obtained when your head was moved vigorously?
Ally Love and Bob Wilson
Coleraine, County Londonderry
Lucky mark: Local birds tend to eat little black insects. So how come they
void themselves on me from a great height with a white and annoyingly
conspicuous product?
M. Rogers
Great Hockham, Norfolk
Soggy pud: The traditional way to cook a boiled pudding is to tie it in a
cotton or linen cloth and immerse it in boiling water. If the water goes off the
boil, water gets into the pudding and it goes soggy. What prevents the simmering
water鈥攗ndoubtedly a liquid鈥攑enetrating the cloth, when the cloth
lets in water when the temperature is only a few degrees lower?
Lorna English
London