You have seen rain fall and splatter on the ground.  You have seen snow twirl and land softly.  You have seen shooting stars fly through space.  You have seen leaves drift out of trees.  What is it like to fall so far?  Why do some things fall faster than others?  If you are falling, can you choose how fast you go?  There's only one way to answer these questions.  We must skydive for science!


Oh, did I not tell you we are in a plane?  Well, we are.  We are 13,000 feet in the air, and you are wearing a parachute.  There's a farm way down below.  The cows, the fields, and the barn look as small as toys.  Ready?  Jump!  ZOOM!  JUST TELL ME WHEN YOUR STOMACH SETTLES DOWN!  GOOD?  GOOD!  Right now you are in free fall, which means you are falling with nothing pushing or pulling on you.  You were not thrown.  You are not being pulled by a giant rope.  The only thing that is pulling you is gravity.  You are just falling.  So sit back and relax.  Actually, spread your arms and relax.  Now listen to this science lesson in the middle of the air. 

This is so easy. Look ma, no hands?


Faster, faster, faster . . . You may have seen that some things, like rain, fall straight to the ground and splash there.  Other things, like snow, will sort of drift, taking their time before landing softly.  Drag is the word for the way that air slows things down as they move through the air.  It may not seem like it, but everything is pulled down with the same force, no matter how heavy or light it is.  It's the shape of a thing that will change how much air hits it and slows it down.  You can test this right now.  By changing your shape, you can change how much drag you have.  Think of diving into a pool.  Your straight body pierces the water, going deep.  Now think of belly-flopping into a pool.  Ouch!  Your whole body hits water, so there's much more stuff to stop.  Up here in the air, spread out your limbs so air is hitting more of your body.  Great.  Now point your head down, so you're like an arrow, shooting toward Earth.  And you're off!  SHHHHHHHOOOOOOOMMMMMMMMM.

Wait, did I grab flippers instead of a parachute?


We can't see air, but it's there in millions of parts, pushing up against you as you fall.  All of this air slows your body down.  Think of these parts of air as being like jumping into a ball pit.  All of those balls stop your body from going straight down and hitting the ground.  They hold you up like a cushion.  But they also rub against you as you fall.  Friction is the force that slows things down when two things rub together.  You are being slowed by the air rubbing up against you.  You may not be able to see the air, but you can hear it roaring in your ears.  You can feel them pulling your cheeks back into a big smile.  Your cheeks flap like flags in the wind.  Do not worry, both of us look ridiculous.

This looks a lot safer than skydiving.


So gravity is pulling you down, making you go faster and faster.  At the same time, the air is making a cushion that slows you down.  Who wins?  Well, gravity, of course.  There is not enough air to stop you.  This is a good thing.  I would hate to leave you floating in the middle of the sky.  Your teacher would be so mad at me.  That doesn't mean that the air is not really strong.  In fact, when it equals the pull of the Earth, you stop speeding up.  You keep going the same miles an hour.  Terminal velocity is the fastest that something can fall.  You just reached 125 miles an hour!  Good thing there are no speed zones up here.


Time to pull that parachute.  Catch!  Now your chute is nice and wide to catch a lot of air so the drag will slow you down.  Nice.  As we drift toward the ground, think about your shape falling down from the air.  You are hitting all that air along the way as the Earth drags you back down, and you hit terminal velocity, the fastest you can go while falling.  If only every class could be this much of a head rush.  Next week: Snoring for Science!  Just kidding.

Wait a minute. Am I going to land in the pig pen?


References:

Science.  "Head rush terminal velocity"  Discovery, 2011.  <http://science.discovery.com/tv-shows/head-rush/videos/head-rush-terminal-velocity.htm>

National Geographic Eduction.  "Terminal Velocity"  National Geographic, 2012.  <http://education.nationalgeographic.com/education/media/terminal-velocity/?ar_a=1>