Ask Mr. Science
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What happens if the earth gets cut in
half?
This was a great question, which led to a number of topics. First of all,
what would happen if half of the earth would magically disappear?
The most important concept here is that the earth is mostly a liquid, not
a solid. To show what would happen to a half-sphere of liquid in space, I
modeled the situation with a blob of salad oil, shaped like a semicircle,
floating on top of water.
[In a casserole dish, pour 1/2" water; Out of a
few thicknesses of aluminum foil, make a 1" high wall, in the shape of a
semicircle; stand this in the water, and pour oil on the inside; When you
quickly lift the aluminum foil away, the semicircle of oil will rapidly
shape itself into a circle.]
Just like the oil on the water, the half of the earth will quickly shape
itself back into a (smaller) sphere, in the process of which the remaining
surface will crumble and crack, and probably re-melt completely.
What about a smaller earth? All we have to do is look in the neighborhood, to mars or the moon. Mars is a little smaller than the earth, and the moon even smaller. The smaller they are, the less gravity they have, andthe faster they lose their atmospheres - mars has a little left, the moon nothing. Second, small objects cool faster: the moon is frozen solid already. Why do we care - after all, if the earth turned solid, there would be no more earthquakes, no more volcanoes. However, after a while, all the carbon would end up on the ocean floor, ... (more text) Here are some links I found:
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Margins of error
Margins of error are an important concept in experimental science.
This morning at breakfast there was this article on the front page of the
Santa Fe New Mexican, showing
the results of a poll taken in the race for the 3rd congressional district.
It showed Udall with 42%, Redmond 35%, Miller 8%, undecided 15%.
If the election were held today, I asked the kids, who would win? This was a great question, which led to a number of topics. First of all, what Volcanoes, Earthquakes, and Plate Tectonics |
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How many stars are there
in the universe?
I don't have a copy of Carl Sagans book to look up how many billions and
billions he thought there were, but here's my guess: Just this week there
was a nice article in Scientific American (Oct 98) on our own galaxy and
its close neighbors. There I found the estimated number of stars in our
own galaxy: about one trillion. The next thing to find out is how many
galaxies are there in the universe? For that I went to the Hubble Space
Telescope. In 1995, Hubble made a set of observations called the
'Hubble Deep Field'.
Basically it stared a tiny patch of the sky which
contained no foreground stars or dust clouds, and made an exposure so
long that the faintest, furthest galaxies showed up. The size of the field
was the size of the period at the end of this sentence, when seen at
reading distance. If I assume the dot is 1/2x1/2mm, and reading distance
50cm, it would take about "100%" height=5 000 such fields to cover the whole sky. I
believe there are 1000-2000 galaxies in the HDF picture. So my guess for
the number of stars in the universe is equal to the number of galaxies in
the HDF, times the number of HDF's on the sky, times the number of stars
per typical galaxy, or 1500 x 500 000 x 1000 000 000 000 is
750000000000000000000 stars, or 10**21 when rounded up, which is a
sextillion start. [We talked about how you form the names of big numbers
like that].
Are all these stars sprinkled randomly through space? This is similar to asking if people are distributed randomly on the surface of the earth. People live in small groups in houses, houses are strung together along streets; streets cluster to make towns and cities, and cities can be mostly found along coastlines and rivers. There are vast spaces (oceans, deserts) where hardly a person can be found. Stars similarly congregate: our sun is grouped together with many others in an arm of a spiral-arm galaxy, several arms make up the galaxy; our galaxy is a member of a local group of galaxies, which in turn is a member of the local galaxy supercluster. These clusters can be found along ribbons and sheets of other clusters, and so on up to the largest scales at which we have been able to look. In between the ribbons, sheets and walls of galaxies, there are vast volumes in which hardly a star can be found. be found.
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How come people and dogs live longer
than they did 100 years ago? I don't know about dogs (yet), but
if you look at the links below, it is certainly true for humans over
the last centuries. Check out Japan (83 for women), Sub-Saharan
Africa (50), the middle ages (31), and the last 100 years in Estonia.
Increases in life expectancy is due to sanitation mostly, and then
primary care medicine. The graph on
the top right (stolen from one of the links below), shows an
interesting trend: although your chances at birth are getting better
and better, the maximum age has not risen much at all.
The maximum life span of humans seems to be pretty much fixed, but
more and more people are getting up there.
I could not find much about dogs, but the part about medicine should hold true for dogs too. Are things getting better for horses too? You'd think that continuous advances in training, medicine and careful breeding would produce ever faster race horses. This seems to be true if you look at short-distance races, where records regularly get broken. However, for longer races this is not true. Why? Nobody knows. (SciAm xx 1991).
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