Activity 2 – Pop rockets

Yes, it is Rocket Science!

Objective

The objective of this lab is to build your own “pop rocket” and to measure its performance while changing the amount of “fuel”.

Theory

For every action there is an equal and opposite reaction.  This is called Newton’s Third Law.

Blow up a balloon and then let the air escape.  Notice that as the air moves in one direction, the balloon moves in the opposite direction.

This balloon is actually a rocket.

In this lab, you are going to control your rocket better.

When the fizzy tablet is placed in water, many little bubbles of gas escape. The bubbles go up, instead of down, because they weigh less than water. When the bubbles get to the surface of the water, they break open. All that gas that has escaped from the bubbles pushes on the sides of the canister.

Now when you blow up a balloon, the air makes the balloon stretch bigger and bigger. But the little film canister doesn’t stretch and all this gas has to go somewhere! Eventually, something has to give.  So the canister pops its top (which is really its bottom, since it’s upside down). All the water and gas rush down and out, pushing the canister up and up, along with the rocket attached to it. Real rockets work kind of the same way. But instead of using tablets that fizz in water, they use rocket fuel.

Space Shuttle Launch from Cape Canaveral

The rocket that launched Deep Space 1 on October 24, 1998, had four different kinds of engines. Some pushed the rocket off the ground. Then some helped it continue its climb into space. Others gave the Deep Space 1 spacecraft its final push away from Earth. But all of them forced a gas to shoot out of the rocket, thus pushing the rocket the other way.

We call this wonderful and useful fact the law of action and reaction. This is Newton’s third law.  The action is the gas rushing out of the rocket. The reaction is the rocket taking off in the other direction. In other words, for every action there is an equal and opposite reaction. The rocket goes in the opposite direction from the gas, and the faster the gas leaves the rocket, the faster the rocket gets pushed the other way.

Hints: Keep in mind: Just like with real rockets, the less your rocket weighs and the less air resistance (drag) it has, the higher it will go.

Force = mass x acceleration is Newton’s second law.

Inspired by “Make a Pop Rocket” from http://spaceplace.jpl.nasa.gov/rocket.htm

Materials:

Plastic 35-mm film canister

The film canister MUST be one with a cap that fits INSIDE the rim instead of over the outside of the rim. Sometimes photography shops have extras of these and will be happy to donate some for such a worthy cause. Fuji Film is the best brand to use.

Effervescing (fizzing) antacid tablet

The kind used to settle an upset stomach such as Alka-Seltzer)

Water

Eye protection (like eye glasses, sun glasses, or safety glasses)

Paper Towels

Optional to make a paper covering for your rocket.

Paper, regular 8-1/2- by 11-inch paper

Cellophane tape

Scissors

Procedure:

Assemble a “pop rocket” as shown.

Lid

Tablet

Canister

              Before                                       After  (stand back)

Blasting Off Instructions

1. Put on your eye protection.
2. Turn the rocket upside down and remove the canister’s lid.
3. Fill the canister one-half full of water.

Now work quickly on the next steps.

4. Drop one-half of an effervescing antacid tablet into the canister.
5. Snap the lid on tight.
6. Stand your rocket on a launch platform, such as your sidewalk or driveway. The lid goes “down”. The lid touches the sidewalk.
7. Stand back and wait. Your rocket will blast off. It might take as long as one minute.
8. Measure the height to which it flies using ½ a tablet when it is one-half full of water

Predict:

What will happen if you add more water?  Will it go higher or not so high?

What will happen if you add more tablets, or more fuel?  Will it go higher?

What do you predict is the best combination of water and tablets to reach maximum height?

Observe:

To achieve the greatest height, the best amount of water to use was ___.

To achieve the greatest height when the rocket is  ___________ of water, the best tablet size is   _____________.

Explain:

Reflect (optional)  How might I use this activity in my class?