Balloon Rockets
You don't need an advanced degree in rocket science to learn some things about Pathfinder's take-off and landing. Here are two activities you can do at home with ordinary materials.
Do-it-Yourself Rocketry
What It's All About
A rocket's movement depends on Newton's Third Law of Motion: For every action there is an equal and opposite reaction. When a rocket blows out gas at high speed in one direction (action), the rocket is pushed in the opposite direction (reaction). The
gas pushes against the rocket and the rocket pushes back just as hard against the gas.
What You Need
- Balloon—long, thin type
- Clothespin—spring type
- Drinking straw
- String—at least 1.5 meters (5 feet) long
- Tape—Scotch or masking
What to Do
1. Inflate the balloon, but do not tie it. Instead, use the clothespin to clamp it shut securely.
2. Release the clothespin. What happened?
3. Reinflate the balloon and clamp it shut with the clothespin again.
4. Thread the string through the drinking straw. Tape the long side of the balloon along the length of the straw.
5. Either tape the ends to two opposite walls or have two people hold the ends. Whichever you do, make sure the string is taut.
6. Slide the balloon-straw assembly along the string until the clamped end reaches the wall or the end of the string held by a person.
7. Release the clothespin.
What Happened?
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Why?
The balloon works the same way as a rocket does. The compressed air (gas) inside
the sealed balloon pushes outward in all directions, but as long as the gas can't go anywhere, neither can the balloon. As soon as you release the clothespin, the gas blows out the back at high speed (action). It pushes the balloon away in the opposite
direction (reaction).
A space rocket works in basically the same way as a balloon rocket except that a space rocket doesn't expel all the compressed gas at once. It burns fuel to resupply the compressed gas and keep the reaction going over a longer period of time.
Question: Suppose you are in a spacesuit drifting weightless in space some distance away from your spaceship. You have run out of compressed gas for your mini-thruster. Fortunately, you happen to have a bag of baseballs. What can you do to get back to your spaceship?
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