A Reaction to an Action

Like a rubber band, the skin of a balloon is madefrom an elastic material. When the balloon is inflated, this skin stretches. The stretched skin stores energy. When the balloon deflates, the stored energyis released. By understanding this transformation, you can harness elasticmaterials to power all sorts of things, including a simple rocket balloon.

Materials

□ severalballoons of different shapes and sizes

□ index cards

□ a pair ofscissors

□ a pencil

□ safety gogles

To Do

Use your scissors to make two side by side snips into theindex card. The snips should be about 1 inch (2.5 cm) apart and placed in thecenter of the card's shorter side. These snips will form the edges of abendable tab.

Using a pencil, punch a small hole in the center of thistab. Inflate a balloon. While preventing the air from escaping, slip the neckof the balloon through the hole. Put on safety goggles. Release the balloon. What happens?

Try launching several other balloons. Can you improve thecard design to produce a better and more stable rocket?

TheScience

When stretched, the balloon skin developed a strong elasticforce. This force pressurized the air trapped within the balloon. When thepressurized air was allowed to escape, it rushed vigorously from the balloon'snozzle.

English physicist Sir Isaac Newton's Third Law of Motionstates that "for every action, there is an opposite and equalreaction." In this example, the action was the jet of air escaping fromthe balloon nozzle. The reaction was the movement of the balloon in theopposite direction from the air jet.