

Your group will discover that math can be useful for judging how well a particular rocket performs. They will learn the value of representing the real world with a diagram, because drawing a diagram lets them figure out the height of the rocket's flight, something that's hard to measure directly. Before you do
this activity with your group, you need to complete Height
Site. In
that activity, people build inclinometers, devices that will enable
them to measure how high their rockets fly. After launching the rocket, blow into the PVC pipe to reinflate the soda bottle so you are ready to launch again. We suggest that you put your hand around the end of the pipe to make a mouthpiece and put your lips against your hand. Before you begin
building rockets, you might check to see that all members of the group
have the inclinometers that they made in the Height
Site activity.
They'll need their inclinometers to measure how high their rockets
fly. While everyone is
making rockets, we suggest you establish a launch order. We suggest that
you have people sign up for launch order only after they have completed
a rocket. You could say something like: "Come up and show me your
rocket, and I’ll sign you up for a launch time." It’s important
to establish who is launching when before you go to the launch site. (At
the launch site, things can get a little chaotic.) Have everyone fill
in the names, in order, on their data sheets before going to the launch
site. When people are using
their inclinometers to follow a rocket’s flight, it’s important
that they keep both eyes open. This makes it possible to track the rocket
in flight. They can either sight through the tube with both eyes open
or sight along the top of the tube. Either method will work. The important
thing is to keep both eyes open. Mention this to your
group. Tell them that you’ll do a couple of trial runs, so that everyone
gets a chance to practice. Aimers
are responsible for holding the PVC pipe straight up and making sure the
rocket doesn’t hit anyone (including themselves). We suggest you
appoint responsible people to be Aimers, so that rockets are not aimed
or fired at people. The
Aimer also reinflates the soda bottle after each launch by blowing into
the PVC pipe. Here
are the steps you will follow at the launch site:
(Marking the launch site and the 10meter distance from the site could be done ahead of time as part of preparation, before you take your group to the launch site.)
Each member of your
group needs a Rocket Launch Data Sheet
on which he or she has written the launch order. Each person also needs
a rocket, an inclinometer, and a pen or pencil. You also need your
rocket launcher and a spare bottle or two, your 10 meters of string, and
some way to mark the launch site and a circle that’s 10 meters from
the launch site. You can mark with chalk if you’re on asphalt, with
tape if you’re in the gym, with sticks or rocks if you are on grass. First, mark the launch
site. To accurately measure the rocket’s height, people need to view
the rocket launching from a specific distance away. Have someone hold
one end of your 10meter string on the launch site while someone else
stretches out the other end and marks an arc that is exactly 10 meters
from the launch site. Everyone watching the launch will stand on the edge
of this arc. Then do a trial launch.
Have everyone do a countdown, chanting together: "3, 2, 1, Launch!"
On "Launch!" the Launcher stomps down on the 2liter bottle,
sending the rocket flying. Have everyone use inclinometers to measure
the height of the rocket’s flight. Have people compare
their inclinometer measurements. It will take some practice before people
are comfortable using their inclinometers to track a rocket. Start launching rockets,
in the order that you previously established. Ask everyone to measure
the height of each rocket’s flight and record it on his or her data
sheet. If you can, measure the height of each rocket yourself—so
you can check the readings of others. When we do this activity at the
Exploratorium, we stop after each launch and announce the measurement
we got. If you have time,
you might want to have everyone launch his or her rocket twice, then use
their best height. After you finish launching
rockets, go back inside to figure out how high the rockets flew. The height of the
triangle is how high the rocket flew above eye level. To get the height
the rocket flew above the ground, people need to add on the distance from
the ground to the eye. We've provided an average value for this number.
People could get a more accurate measurement by measuring the eye level
of all their measurers and figuring out the measurers’ average eye
level. But that's more accurate than people probably need to get! Why Use an Average Angle Measurement? Some people may ask why they had to average three measurements. People often think of measuring as exact, but it isn't really. Every measurement is an estimate, a best guess at an answer. When you are using a new tool, like an inclinometer, different people will come up with different estimates. Averaging these measurements improves the accuracy of your results.
Going
Further—Building a Better Rocket You might want to
talk with your group about what changes might make a rocket fly better.
Here are some things you might want to encourage them to think about. To move through the
air, a rocket has to push air aside. Things
that travel fast—like sports cars and jets—are shaped to minimize
the amount of air they have to push aside to move forward. The fins on
the back of a rocket help it slide through the air easily with its nose
forward. People might want to experiment with adding more or fewer fins
or using differentsized fins. Ask them to imagine
that they are pushing a kid on a wagon. With the same push, they can make
a little kid in a wagon roll farther than a big kid. The rocket launcher
gives your rocket a push with a puff of air. If two rockets have exactly
the same design and weight distribution, a lighter rocket will fly farther
with the same push than a heavier one. Can they make their rockets lighter?
Ask them to think
about what other changes they could make. Do long rockets fly higher than
short ones? Do some people make better Launchers than others? Have people
work together to see how high they can make a rocket fly. So far, people have
been launching rockets straight up to see how high they will fly. Now
ask them to try launching rockets to see how great a distance they can
get a rocket to fly. To get the greatest height, people held the launcher so it pointed straight up. To get the greatest distance, they’ll need to change the angle at which they hold the rocket launcher. What angle gives them the greatest distance? Encourage them to experiment to find out.




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