|
Module 5 A Lesson in a Lab 【美文阅读】 How to create a rocket balloon To create a rocket balloon, you'll need the following items: a balloon (any size), a piece of string (10 to 25 feet), a straight drinking straw (吸管), tape. First, you have to create a “track” for the rocket balloon to run on. You begin by tying one end of the string to a tree, post, chair, or any other strong support. Then slide (使滑动) the free end of the string through the drinking straw. Tie the other end of the string to another support (generally at the same height). Make sure the string is taut(绷紧的) when tied down. Move the straw to one end of the string. Fill the balloon with air. Hold the neck tightly to keep it full. Using two pieces of tape to attach the balloon to the straw. The mouth of the balloon should point toward the nearest support. Then release the balloon and watch it go! When the mouth of the balloon is held closed, the air in the balloon has nowhere to go, so it pushes back to keep the balloon's shape. However, since the mouth is open when you release it, the air has somewhere to go. The air pushes out the mouth of the balloon. Since the air is now moving, the rocket balloon also moves. This follows Newton's Third Law of Motion (for every action there's an equal and opposite reaction)． There is friction (摩擦) between the string and the straw, but the straw is made of material that's smooth and the weight of the balloon and straw is light, so the overall frictional force is very small. | 
