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# Try This: Balloon Rocket by Tom Robinson

Once you have seen what causes objects to move in a certain direction, you are ready to think about how they get going in that direction in the first place. If you've ever seen a space shuttle take off, you probably noticed a huge cloud of gas and fire coming out of the back end as it lifted off. Why do rockets have to burn so much fuel to make the shuttle go?

## QUESTION

How do rockets work?

## MATERIALS

• Latex balloon
• Long string
• Plastic straw
• Tape

## PROCEDURE

1. Blow up the balloon and hold the neck with your fingers so no air escapes.

2. Hold the balloon in front of you and let go of the neck. Observe the motion of the balloon.

3. Feed the string through the straw and attach both ends of the string to a wall or other solid support so that the straw is suspended above the floor of the room.

4. Blow up the balloon and hold the neck as before.

5. While holding the neck of the balloon, tape the balloon to the straw. Stand back and let go of the balloon. Observe the motion of the balloon.

## WHAT'S HAPPENING

To make something move, there must be a force on it. While nothing appears to push on your balloon, there really is something making it move — air! When the balloon releases its air, the air particles that escape encounter other air particles outside the balloon. Each group of air particles experiences forces from the other. That is why you can feel the air coming out of the balloon. But it's also what makes the balloon move.

This is an example of another Law of Motion discovered by Isaac Newton, the one commonly known as Action/Reaction. It says that every action (the air escaping and pushing on the outside air) has an equal and opposite reaction (the outside air pushing back on the air in the balloon, and making the balloon move). Rockets work in the same way, but instead of using inflated balloons, they use huge engines burning very powerful fuel.

## Silly Experiments …

Why did the scientist take the ruler to bed?

To see how long he slept!

Why did the scientist put sugar under her pillow?

To see if she had sweet dreams!

Why did the scientist sit on her watch?

To see what it was like to be on time!

Why did the scientist keep a ruler in his laboratory?

To see if he could keep his facts straight!

## KIDS' LAB LESSONS

QUESTION: What makes a swing go?

EXPERIMENT OVERVIEW: In this experiment you will be setting up several swing like devices, called pendulums, to test what makes them swing faster and slower. You will experiment with the length of the swing, the weight hanging off the pendulum, and the size of the swing to determine which affect the time it takes to complete one full swing.

SCIENCE CONCEPT: In the 1500s in Italy, Galileo was fascinated with the swinging chandeliers in the cathedral of Pisa. In his laboratory, he set up experiments to test the factors he thought would make the chandeliers swing faster. To make the experiments as similar as possible, he used the term period to describe the time it took to make one complete swing — from one side across to the other and back.

he three easiest factors to test are how long the pendulum is, how much weight is on the pendulum, and how large the swing is. You will have to pick one factor at a time and, while keeping the other two constant, change the factor you chose to determine whether those changes had any effect on the period.

## Words to Know

pendulum: a swinging apparatus formed by hanging a weight from the end of a long string.

period: the time it takes a pendulum to complete one full swing.

MATERIALS

• Several identical items (for example, spoons, screws, washers, pencils)
• 1 long (36 inches or more) piece of string
• Doorway
• Thumbtacks
• Stopwatch

PROCEDURE

Part I: Weight

1. Tie one item to your string.

2. Attach the other end of the string to the top of the doorway with a thumbtack.

3. Pull the string back and release it at the same time you start the stopwatch.

4. Count 10 complete swings and stop the watch when the tenth swing finishes. Record the time.

5. Attach another item to your string and repeat the experiment. (This picture shows how you can hang the string at different heights.)

6. Record your time and add another item. Repeat this process of adding items until you have four times recorded.

Part II: Size of Swing

1. Remove all but the first item and pull the swing back a small amount.

2. As before, count 10 complete swings and record your time.

3. Pull the swing back a little more than before and repeat the experiment. Record your time.

4. Repeat this process of pulling the swing a little farther back than before until you have four times recorded.

Part III: Length

1. Again, start with just one item and record the time for 10 swings.

2. Shorten the swing by about 4 inches.

3. Repeat the experiment, taking care to pull the swing back the same amount as before. Record your time.

4. Repeat this process of shortening the string by 4 inches until you have four times recorded.

QUESTIONS FOR THE SCIENTIST

• What factor(s) affected the period of the swing?___________________________

• Why do you think the other factors didn't have an effect on the period?________________________________

• When you swing on the playground, what do you have to do to keep from slowing down?___________________________________________________

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#### THE EVERYTHING KIDS' SCIENCE EXPERIMENTS BOOK

By Tom Robinson

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