hey my name is kaeleigh and in this lesson we will talk about air resistance and
how it changes the way we think about gravity
make sure you've already watched the video what is gravity before starting
this one let's get started you may have heard of the scientist named Galileo he
lived a really long time ago but is famous for a lot of discoveries we're
gonna start our lesson with a little story about Galileo Galileo is from a
country called Italy and Italy is famous for a lot of things like pizza meatballs
but it's also the home of a special building called the Leaning Tower of
Pisa it's called the Leaning Tower of Pisa because well it's leaning but we
aren't going to talk about the physics of how a tower leans today but you can't
think about that in terms of some of Newton's laws instead the Leaning Tower
of Pisa is the setting for our story about Galileo you see Galileo went up to
the top of the Leaning Tower of Pisa with a big cart full of things with
different masses like a cannon ball and a musket ball and a brick and a block of
wood and then from the top of the Leaning Tower of Pisa he dropped them in
pairs like the cannon ball and the musket ball which are both round but one
is large and heavy and one is small and light and he dropped them at the same
time what Galileo found was at the cannon ball and the musket ball hit the
ground at the same time and the same thing happened with the brick in the
block of wood even though the brick has more mass than the block of wood they
both hit the ground at the same time and this is how Galileo was able to prove
the gravity effects objects the same way regardless of the object's mass how
and light objects hit the ground at the same time when they are dropped from the
same height now let's test Galileo's theory at home for this experiment you
will need two envelopes and two sheets of paper now you're going to fold both
sheets of paper into thirds or fourths which ever way fits into your envelope
and you're going to stick both sheets of paper into one envelope so now you will
have one empty envelope and one envelope with two folded sheets of paper in it go
ahead and seal them shut when you're ready you can pause the video here to
prepare your materials so now what do you think would happen if you brought
your two envelopes up to the top of the Leaning Tower of Pisa and dropped them
which envelope will hit the ground first find a piece of paper and jot down your
hypothesis we're prediction we can make our own Leaning Tower of Pisa ask an
adult for supervision and stand on a step stool or a really stable chair then
hold the envelopes at eye level so the flap is facing the ceiling make sure
they are level and then you're going to drop the envelopes go ahead and pause
the video here to try out your experiment
welcome back well what happened was your prediction correct you should have found
just what Galileo found just like the cannon ball and the musket ball objects
of different masses fall to the earth at the same speed now figure out which one
of your envelopes is the empty one and you're going to crinkle it up into a
paper ball so now you'll have one paper ball envelope and one envelope with two
pieces of paper that's still nice and flat even though one envelope is in a
crinkled up ball the envelope with paper in it still has more mass now we're
going to take our new materials to the Leaning Tower of Pisa which one do you
think will hit the ground first this time
jot down your hypothesis now get back up on your chair and make sure your new
materials are at the same height so they have the same distance to fall that
means the bottle of the bottom of the crinkled up ball will be at this same
level as the bottom of the envelope or the flat part of the envelope go ahead
and pause the video here and run your experiment welcome back
well did it feel like I tricked you did you observe that the crinkled up ball
hit the ground first but how could that be it's lighter than the full envelope
there's one thing that Galileo failed to think about when he was doing his
experiment atop the leaning tower of pisa air resistance air resistance is
also called drag and drag opposes the motion and slows an object down
it's like friction but with air the easiest example to think of is with a
rock and a feather of course we expect the rock to hit the ground first but not
because it has more mass remember gravity acts the same on all objects
regardless of mass but because of air resistance the feather will experience
more air resistance and so then the feather will take longer to reach the
ground but if we dropped the rock and the feather on the moon a place that has
no air and therefore no drag the feather and the rock would hit the ground at the
same time can you think of a time when it would be useful to have
resistance when could you use it to help you to slow down a fall so parachutes
use air resistance to help humans fall safely to the ground they do this by
using drag to reduce the speed the person is falling at since air
resistance can be helpful it's good to know how to increase air resistance one
way is to increase surface area the larger the parachute the more air
resistance it will experience another way is to increase the speed of the
moving object have you ever stuck your arm out of the
window when the car is moving you'll feel a lot more drag when the car is
moving fast versus when the car is moving slow you can also test the
surface area and areas distance this way - do you feel a difference if you point
your palm straight out versus down or forward when your palm is facing forward
you have more surface area exposed in the direction of motion and you'll feel
more drag thanks for exploring air resistance with me there is a fun
activity to go along with this video called test parachutes where you get to
design parachutes and using what you know about air resistance I'm sure he'll
be a great parachute engineer have fun and remember to always be clever