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You are viewing the 4th Grade: Physical Science Collection

# Blast Off! Rocket Science

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Is your child a rocket scientist in the making? Here's a fun activity that illustrates the basic principles behind what makes rockets rock!

### What You Need to Know

Aerospace engineering is the branch of engineering concerned with the design, manufacture, and operation of launch vehicles, satellites, spacecraft, and ground-support facilities for the exploration of outer space. One type of spacecraft is a rocket, which is powered by gases that are forced out of one end.

Rocket-like devices were demonstrated about 360 B.C. By the Greek mathematician and scientist Archytas (428-350 B.C.). So while some form of a rocket has been in existence for many years, the science of how a rocket works was first described by the British scientist Sir Isaac Newton (1642-1727) in 1687. Newton stated three important scientific principles that govern the motion of all objects, whether on Earth or in space. These principles, now called Newton's laws of motion, provided engineers with the basic knowledge necessary to design modern rockets such as the Saturn V rockets and the Space Shuttle Discovery.

### What You Need:

• 6 feet (1.8 m) of string
• 4-inch (10 cm) piece of drinking straw
• 2 chairs
• 9-inch (23 cm) round balloon
• Spring clothespin
• Transparent tape

### What You Do:

1. Thread the string through the straw
2. Tie the ends of the string to the backs of the chairs
3. Position the chairs so that the string between them is as tight as possible
4. Inflate the balloon. Twist the open end of the balloon and secure it with the clothespin
5. Move the straw to one end of the string
6. Tape the inflated balloon to the straw
7. Remove the clothespin from the balloon

### What Happened

The straw with the attached balloon quickly moves across the string. The movement stops at the end of the string or when the forces acting on the balloon are balanced.

### Why?

When the inflated balloon is closed, the air inside pushes equally in all directions. The balloon doesn't move because all the forces are balanced. When the balloon is open, the action-reaction pair of forces opposite the balloon's opening is unbalanced. One force is the walls of the balloon pushing on the gas inside the balloon. This force pushes the gas out of the balloon's opening. The other force is the gas pushing on the balloon's wall opposite the opening. This force pushes the balloon in the direction opposite the opening.

Reprinted with permission from "Engineering for Every Kid" by Janice VanCleave (Jossey-Bas, 2007)

Updated on Jul 22, 2014
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