Bottle Blast-Off! combines science and math in an exciting activity. This activity involves making and launching rockets, using an inclinometer to measure each rocket's flight, and figuring out how high each one flew.

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.

Building a Rocket Launcher

You can build rocket launchers by following the directions on Building a Rocket Launcher. Or you can have a few members of your group build rocket launchers as a project. Building a launcher is easy; once you have gathered the materials, the project will take five to ten minutes.

A group of fifteen people can use one rocket launcher, but we suggest you make two—in case one breaks. We also recommend having an extra soda bottle handy just in case you need a quick replacement.

Introducing the Activity

At the Exploratorium, we introduce this activity by launching a rocket once, inside the room, just to show the group how cool it is. If you do this, be sure to point the launcher away from the group, in a direction where the flying rocket won't hurt anyone or anything.

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.

Making Rockets

Have your group follow the instructions on Making Rockets or lead them through the steps to make a rocket.

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.

Before You Go to Your Launch Site

Here are a few preparations that will make it easier to keep track of what’s going on at the launch site.

Review how to use the inclinometer
If you need help remembering how to use it, see Height 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.

Designate an Aimer and a Launcher
Each time a rocket is launched, you’ll need an Aimer and a Launcher. The Launcher stomps the bottle with one foot to launch his or her own rocket. We suggest that you have each person be the Launcher for his or her rocket.

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.

Tell Everyone How the Launching Will Work

Here are the steps you will follow at the launch site:

 First, you will mark the launch site. Then you will mark part of a circle that’s 10 meters from the launch site. Everyone who is measuring the rocket’s height will stand on this arc, so each person is 10 meters from the launch site. Each person will launch his or her own rocket with the help of the Aimer. Everyone else will watch to see how high the rocket goes and will mark the results on a Rocket Launch Data Sheet.

(Marking the launch site and the 10-meter distance from the site could be done ahead of time as part of preparation, before you take your group to the launch site.)

Launching the Rocket

Here’s What to Take 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 10-meter 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 2-liter 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.

Blast Off!

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.

Figuring Out How High Each Rocket Flew

Have people use the Rocket Height Calculator to figure out how high each rocket flew. The procedure here is very similar to the procedure you followed in Height Site.

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

After your group has launched rockets, they may want to see if they can build better rockets. If they do, we suggest that you spend another session trying to improve rocket designs.

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 different-sized 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.

Going Further—Another Experiment to Try

If your group wants to keep experimenting with rockets, here’s another experiment to try. You’ll need a big space (like a playground or a football field).

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.

 Quick Links: Making Rockets Building a Rocket Launcher Launching Rockets Rocket Height Calculator Tips for Leaders A Leaders Guide Print Outs: Rocket Launch Data Sheet Rocket Height Calculator Grid