Page 79 - BBC Focus - August 2017
P. 79
DR ALASTAIR ALEX FRANKLIN- DR PETER PROF ALICE PROF MARK CHARLOTTE
GUNN CHEUNG J BENTLEY GREGORY LORCH CORNEY
Astronomer, Environment/ Computer Psychologist, Chemist, Zoo director,
astrophysicist climate expert scientist, author sleep expert science writer conservationist
DR HELEN DR CHRISTIAN EMMA LUIS DR AARATHI PROF ROBERT
SCALES JARRETT DAVIES VILLAZON PRASAD MATTHEWS
Oceans expert, Neuroscientist, Heath expert, Science/tech Biologist, Physicist,
science writer science writer science writer writer geneticist science writer
Y OU R QU E S TI O N S AN S WE R E D
AUGUST 2017 EDITED BY EMMA BAYLEY
Why do rockets follow
a parabola after
launch?
FRED WILHELM, US
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-
range rockets, things are more complex. For example, air
resistance must be taken into account. But even ignoring that,
a projectile doesn’t really follow a parabola – because the
Earth isn’t flat. This means that gravity doesn’t simply pull
objects straight back down. Instead, it pulls them towards the
centre of the Earth, whose direction changes as the projectile
moves further down-range, away from the launch site.
Detailed calculations then reveal that the true trajectory is
not a parabola, but part of an ellipse. RM
PHOTO: SPACEX
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