The Physics of Skydiving (Science Out Loud S2 Ep1)


[MUSIC PLAYING] The MIT Skydiving Club just
jumped out of an airplane. It might seem like a
wild adrenalin rush, but actually, there’s
a lot more to skydiving than just jumping out of a
plane and pulling a ripcord. Skydivers can
control their falls. They can sit, track, flip, fly
head-down, make crazy hybrids, and even fly over to
each other to dock. When you’re just
falling a few feet, there’s not much you
can do on the way down. So how is falling
thousands of feet through the sky any different? You learn in school that things
accelerate towards the ground because of gravity. But when things like skydivers
fall for thousands of feet, another force becomes important. Drag. Gravity pulls skydivers
toward the Earth. But as we fall, tiny air
molecules bump into us. Each tiny bump
causes a little bit of force against our bodies. The hit from one air molecule
may not seem like a lot. But when you add all
those tiny forces up, you get a big force called
drag, which pushes up opposite to gravity. You can feel drag when
you stick your hand out of a moving car window. When the jumpers
first leave the plane, there’s not much drag
acting against gravity, so they accelerate
towards the Earth. As skydivers fall and speed
up, the drag force grows, and the skydivers feel the force
of more and more air molecules. But with this comes control. And by positioning
our bodies, we can stop flipping by
pushing against the air. So what if Banks and I
want to jump together? Can we fall at the same speed? Swati has a lot less
surface area than me, so you’d think that
she’d fall faster. But actually, she’s so
much lighter than me that she has a tendency
to fall slower. But by reducing how much
surface area is exposed to the air molecules, I
can reduce drag and keep up with Banks. Drag can be used
for more than just speeding up or slowing down. With your arms at
the side and legs out generates extra
airflow at your feet, which pushes your body in the
direction it’s facing. This is called tracking. To really use drag,
air needs to push you hard enough, which
can only happen if you’re going fast enough. And that’s why you
can’t track when you jump off of a high
dive at a swimming pool. Skydivers can also
do things like turn in place to create
formations with each other. Other positions, like sitting,
standing, and head-down, change the surface area as the
jumper is exposed to the wind. Since fewer air molecules
hit their bodies in these positions,
skydivers can reach speeds up to 200 miles an hour. Skydivers would prefer,
though, to not hit the ground at 200 miles an hour. Because they can’t change
the pull of gravity, they need to have as
much drag as possible. So they open a parachute. The large surface
area of the parachute helps us to slow down
so we can land safely. Skydiving may seem like it
defies the laws of physics. But in the end, it’s just
playing with the wind. [MUSIC PLAYING]