- Every so often, one comes across facts
that take one aback. Take the warning issued earlier this month by an American
scientist about the lethal dangers of clearing snow.
-
- Anyone who has shovelled snow knows that
what starts out as fun rapidly turns into rather hard work.
-
- Before long, the scarf, hat and gloves
are off. Then the coat. After 20 minutes, one could cheerfully be shifting
the stuff sporting nothing but boots and a builder's crease.
-
- A back-of-the envelope calculation by
Prof Dr Daniel Black, of Wartburg College, Indiana, reveals why. Roughly
speaking, six inches of snow is equivalent to one inch of rain. And rain
is water - one cubic foot of which weighs about 62lb. So clearing a three-inch
dusting of white, fluffy snow from an area, say, 30ft by 30ft, is equivalent
to heaving a ton of the stuff aside. No wonder more than a few people drop
dead doing this simple chore each winter.
-
- It is one of those "strange but
true" facts that I shall be adding to a mental list I began when,
aged six, I first read that if you could get a bowl of water big enough,
the planet Saturn would float in it like a rubber duck.
-
- I have been adding to this list ever
since. Some simply reveal the miracles of nature. For example, the fact
that each cell in our bodies is packed with about a yard and a half of
DNA; or that we share 30 per cent of our genetic make-up with leaf spinach
(vegans please note).
-
- Another - and this one is of particular
relevance this year - is that the Earth is the only planet in the solar
system whose moon is at precisely the right distance to cover the Sun's
face exactly during an eclipse.
-
- Not that the man-made world is bereft
of strange-but-true facts. I recently learned that the weight of the Eiffel
Tower is so elegantly well-distributed that it presses on its foundations
more lightly than a man sitting on a chair.
-
- Best of all are those phenomena whose
surprising nature hints at profound truths - if one only has the wit to
spot them. None better illustrates this than the bizarre fact that if you
drop a brick and a bulldozer off a bridge, they will hit the ground at
the same time.
-
- Why on earth should it be that the weight
of something makes not a shred of difference to how fast it falls?
-
- The explanation for this fact - first
demonstrated, according to legend, by Galileo dropping weights from the
Leaning Tower of Pisa - is in fact rather simple, and rests on the fact
that "mass" actually affects two key properties of objects.
-
- The first, most obviously, is how hard
they are pulled to Earth by gravity. As Newton told us, the more massive
an object, the stronger the gravitational force it feels.
-
- But there is a second, altogether more
mysterious property also linked to mass - the inertia of objects. That
is, their reluctance to respond to imposed forces. As we all know, the
more massive an object, the greater its inertia, and thus reluctance to
respond to forces.
-
- So we have a situation in which a brick
is, because of its relative lightness, pulled relatively feebly by gravity,
but responds willingly to that force because it lacks much inertia.
-
- The bulldozer, by contrast, feels the
force of gravity far more strongly, but also possesses far greater inertia,
and thus reluctance to respond.
-
- These two opposing influences exactly
compensate for each other, and the brick and bulldozer hit the ground at
the same time.
-
- This cancelling-out effect is astonishingly
accurate. To date, all attempts to find even the slightest difference between
how strongly a given mass of material responds to gravity and how much
inertia it possesses to compensate have failed.
-
- Exquisitely sensitive experiments have
shown that the level of compensation is exact to at least one part in a
thousand billion.
-
- Quite why this is so remains a mystery.
About 80 years ago, however, this strange-but-true fact about our universe
was used as one of the foundations of an entirely new theory of gravity,
which now underpins the scientific understanding of the entire cosmos.
-
- It takes true genius to see so much in
so little. But then, the author of this theory of gravity was someone called
Albert Einstein.
|
