Page 9 - BBC Knowledge - October 2017 IN

N U M B E RS

25

The percentage of
the world’s
population who eat
chillies every day.

100

The number of tiny
needles embedded into
a painless skin patch
vaccine that could
be used instead of
traditional syringes.
WHY DO ROCKETS FOLLOW A PARABOLA
AFTER LAUNCH? 6,000

Students have long been taught that all projectiles follow a curved path known as a parabola.
The explanation is that, as they fly, they cover distance both horizontally and vertically – but only the
latter is affected by the force of gravity, which bends the path of the projectile into a parabola. For long- The number of
range rockets, things are more complex. For example, air resistance must be taken into account. But, wildebeest that
even ignoring that, a projectile doesn’t really follow a parabola – because the Earth isn’t flat. This means drown during
that gravity doesn’t simply pull objects straight back down. Instead, it pulls them towards the centre of the migration
the Earth, whose direction changes as the projectile moves further down-range, away from the launch every year.
site. Detailed calculations then reveal that the true trajectory is not a parabola, but part of an ellipse. RM

HOW LONG COULD
YOU SURVIVE ON COULD YOU
BEER ALONE? THROW A
FRISBEE ON
Beer typically has around 40 calories per 100ml
(one pint = 568ml). To get your daily 2,000 calories MARS?
just from beer, you’d need to drink 11 pints every
day, which is hardly healthy. But the alcohol is
the least of your problems. Beer, even real ale
or Guinness, contains no fat, almost no protein
and – crucially – no vitamin C. Without any source
of vitamin C, you’ll experience symptoms of scurvy
in two or three months and be dead in six. LV

PHOTO: SPACEX, GETTY X 2 Since the Martian atmosphere is about 100 times less dense than Earth’s, the ‘lift’
a frisbee experiences would also be about 100 times less. But the gravitational
force on Mars is about a third of that on Earth, so a frisbee on Mars would act
as if it is about 33 times heavier (100/3). Since the lift depends on the size of the
frisbee, the angle of attack and the velocity it is thrown (as well as the air density),
it would still be possible to make a frisbee glide, but it would require much more
effort on the part of the thrower! AGu
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OCTOBER 2017