| 2841/
The fact that water expands when it freezes is another anomaly
that is responsible for the presence of life on our planet.
If this didn't happen, the ice would sink to the bottom of
lakes and oceans and they would freeze all the way through,
killing any living organisms in them.
2842/ A steel bridge
across a river in a continental city may well be exposed to
temperatures ranging from 0 degrees to 40 degrees centigrade.
The length of such a bridge may well vary by several feet
between winter and summer, and if the structure is not to
buckle, allowance has to be made for this fact.
2843/ Cool water, and
it will shrink until it reaches a temperature of about 4 degrees
centigrade. Below this temperature, water actually expands
when cooled and shrinks when it is heated. This is why the
water at the bottom of the Earth's oceans does not freeze,
no matter how cold it gets, since water colder than 4 degrees
centigrade will be less dense and will float upward.
2844/ According to the
atomic theory of heat, what we call heat arises from the motion
of molecules, so heat can be thought of as a special kind
of kinetic energy.
2845/ Absolute Zero is
about 273 degrees centigrade below zero ( minus 456 degrees
fahrenheit). The third law of thermodynamics says simply that
absolute zero is unattainable - like the speed of light.
2846/ The first serious
study of the mechanism of plant growth was done by the Flemish
aristocrat Jan Baptista van Helmont. He weighed the dirt in
a pot, then planted a tree in it. He watered the tree for
several years, then weighed the tree and the dirt again. He
found that the tree had gained 164lbs (74kg) while the soil
had lost only a few ounces. Obviously, the material that had
been incorporated into the growing tree had not been drawn
from the soil.
2847/ The substance known
as urea is a typical example of what are called organic molecules.
The molecule is used by most animals to excrete unused nitrogen
that they ingest in their food. Human urine, for example,
contains 2-5% urea.
2848/ The fact that the
total amount of water on the earth is roughly constant has
some interesting consequences. In the last ice age a lot of
the Earth's water supply was locked up in the ice caps that
moved down from the poles, so the level of water in the oceans
was much lower then it is now.
2849/ If you had lived
18,000 years ago, you could have walked from England to Europe
or from Aisa to Alaska on dry land, and the western coast
of England was 100 miles (150km) farther west than it is today.
2850/ The size of a typical
satellite antenna corresponds roughly to the middle of the
wavelength range of microwaves.
2851/ Radiation with
wavelengths from a few atoms across down to sizes typical
of hundreds of nuclei are called X-rays. This radiation can
penetrate living tissue, and is therefore enormously useful
in medical diagnosis. In fact, as was the case with radio
waves, it was not long after these rays were discovered in
1895 that they were put to use, to create the first X-ray
photograph in a hospital in Paris. (The Pasisian newspapers
of the time seemed too interested in the fact that X-rays
could penetrate clothing to recognize their potential in medicine.)
2852/ The lowest-wavelength,
highest-energy part of the electromagnetic spectrum is home
to gamma rays - extremely energetic photons. Gamma rays are
routinely used in cancer therapy to obliterate tumours, but
extreme care has to be taken not to harm the surrounding healthy
tissue.
2853/ The surface temperature
of the Sun is about 5000 degrees centigrade.
2854/ For a beam of light
from a distant star that just grazes the edge of the Sun,
Einstein predicted that the deflection would be 1.75 seconds
of arc (about one two-thousandth of a degree), whereas Newtonian
physics predicted just half of that. Thus the measurement
by Sir Arthur Eddington (1882 - 1944) was a triumphant experimental
confirmation of the theory of general relativity.
2855/ Anthropologists
believe that early modern humans went through a population
bottleneck about 100,000 years ago. This would explain why
humans are so genetically similar to one another. There is,
for example, more genetic variation among members of gorilla
clans in a single African forest than there is among all of
the human beings on this planet.
2856/ French Scientist
Louis Pasteur discovered that wine could be preserved by heating
it. Heating killed the microbes that would otherwise initiate
further reactions which would spoil the wine. This is the
basis of the pasteurization process, still used to make the
milk supply safe in most of the world.
2857/ The density of
the Moon is about 3.6 times that of water - about the density
of the rocks in the Earth's outer layers. But the density
of the Earth is about 5.5 times that of water (the Earth's
core is made of heavy iron and nickel).
2858/ The process of
Photosynthesis traps energy from the Sun and stores it in
chemical bonds in carbohydrate molecules, most notably in
the six-carbon sugar called glucose. When these molecules
are ingested by other organisms, the processes of glycolysis
and respiration extract that stored energy and use it to run
the organism's metabolism. The overall chemical process can
be summarized as:
glucose + oxygen —>
carbon dioxide + water + energy
A simple way to visualize
these processes is to imagine the organism "burning"
the carbohydrates to get its energy.
2859/ Effusion is the
process by which gases leak out of containers through small
(often microscopic) holes. If you've ever thrown a birthday
party complete with helium-filled balloons, only to find the
balloons collapsed the next morning, then you have encountered
effusion. While you were sleeping, the helium in the balloon
leaked out through microscopic pores in the material of the
balloons.
2860/ The average temperature
at the Earth's surface is 15 degrees centigrade.
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