Parachutes work because of something called ‘air resistance.’ If there
were no air resistance, then gravity would cause everything to fall at
the same rate, so no matter what item you dropped (i.e. a feather or a
rock), it would hit the ground at exactly the same time (assuming you
dropped it from the same height). But air resistance complicates things
(and makes sky-diving a lot more fun). Air resistance happens because
as things fall, they have to push their way past the atoms and
molecules that make up air in order to get where they’re going.
For something like a rock, this isn’t really a big deal, since
rocks tend to be really heavy while being pretty small, so they can
push the air molecules out of the way quite easily. But things like
feathers can’t push the air molecules out of the way very well – for
one, they weigh less so they don’t push as hard. And for another,
they’re pretty big, so they run into a lot more air molecules than the
rock does. So the air actually slows the feather down.
This is what makes parachute work. If a person were to fall without
a parachute, they’d push the air molecules out of the way very easily,
so the air wouldn’t be able to do much to slow the person down. But if
the person is attached to a parachute, then the parachute will run into
lots of air molecules, and especially if it’s curved to be higher up in
the middle, it will be very hard for the air molecules to get out of
the way. If they can’t get out of the way, they will slow the parachute
(and hence the person) down.
(published on 10/22/2007)