Exploratorium
Bottle Blast-Off!
Launching Rockets
 

Now that your rocket and launcher are built, you'll want to try them somewhere with plenty of open space for launching. You'll need to bring at least one friend to help hold the rocket launcher while you're stomping the bottle, but to measure the height of your rocket's flight, you'll need at least two more friends, who should bring their own rockets to launch.


You'll also need:

Ten meters (about 33 feet) of string
Something to mark the launch site with (chalk for asphalt, tape for gym floor, or sticks or rocks on a grassy field)
The inclinometer created in Height Site (there should be one inclinometer for every person who will be measuring each rocket's flight).
A Rocket Launch Data Sheet
A pen or pencil


Step 1
First, you need to mark the launch site. To measure the rocket's flight height, at least one person needs to view the rocket launching from a specific distance away. Have someone hold one end of the 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 this arc. The more people who watch and measure the rocket's flight, the more accurate your measurements will be.

Step 2

Before you launch your rocket, the person aiming the rocket by holding the PVC pipe must be sure that no one is in the way of the rocket's flight. The Aimer also reinflates the soda bottle after each launch by blowing into the PVC pipe. We suggest the Aimer put a hand around the end of the pipe to make a mouthpiece for his or her lips when inflating the bottle.


Step 3

Place a rocket on the launcher. Do a countdown, chanting together: "3, 2, 1, Launch!" On "Launch!" the launcher stomps one foot down on the 2-liter plastic bottle, sending the rocket flying.


Have everyone use inclinometers Using Your Inclinometer to measure the height of the rocket's flight.

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. It may take some practice before everyone feels comfortable using inclinometers to track a rocket's flight.

If you have several people measuring the rocket's flight, you can have them average their inclinometer measurements for the most accurate measure of the rocket's height. If only one person is measuring, you might try launching the same rocket several times and recording those sets of measurements for averaging later.

Why Use an Average Angle Measurement? You may 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 the results.


Figuring Out How High Each Rocket Flew

After everyone has taken turns launching rockets, aiming the launcher, and measuring flight with an inclinometer, use the measurements everyone wrote down and follow the directions in Rocket Height Calculator to learn how high your rockets flew.

The height of the triangle is how high the rocket flew above eye level. To get the height the rocket flew above ground, you'll need to add on the distance from the ground to the eye. We've provided an average value for this number. You and your friends could get a more accurate measurement by measuring each other's eye levels and calculating an average eye-level to add to your mesurement—but that's more accurate than you probably need to be!

Going Further

It's easy to see that when the person aiming the rocket holds the rocket launcher pointing straight up, the rocket flies its highest. Can you guess how to make the rocket fly farthest? The launcher could be held at any one of many angles. Which one will send your rocket the greatest distance?

Remember that when you're launching a rocket for distance, the Aimer needs to be especially sure that no one is in the rocket's path.

Size, shape, and weight also affect how far rockets fly. To move through air, a rocket has to push air aside with its pointy nose while the fins at the back help guide the rocket straight through the air. Experiment with rockets that have more fins or fewer, with rockets that are longer or shorter, or with rockets made from heavier or lighter paper. You might even find that some Launchers are just better than others.

 

Next
Rocket Height Calculator

 


For tips on how to use this trick with a class or group, go to the Teacher/Leader
version
 
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