Rockets in the Sky
If someone asked you, What color is the sky? I expect that you would answer, Blue. I am afraid that you would be wrong. The sky has no color. When we see blue, we are looking at blue sunlight. The sunlight is shining on little bits of dust in the air.
We know that there is air all around the world. We could not breathe without air. Airplanes could not fly without air. They need air to lift their wings. Airplanes cannot fly very high because as they go higher the air gets thinner. If we go far enough away from the earth, we find there is no air.
What is the sky? The sky is space. In this space there is nothing except the sun, the moon and all the stars.
Scientists have always wanted to know more about the other worlds in the space. They have looked at them through telescopes and in this way they have found out a great deal.
The moon is about 384,000 kilometers away from the earth. An airplane cannot fly to the moon but there is a thing that can fly even when there is no air. This is rocket.
I am sure that you are asking, How does a rocket fly? if you want to know, get a balloon and then blow it up until it is quite big. Do not tie up the neck o f the balloon. Let go! The balloon will fly off through the air very quickly. The air inside the balloon tries to get out. It rushes out through neck of the balloon and this pushes the balloon through the air. It does not need wings like an airplane.
This is how a rocket works. It is not made of rubber like a balloon, of course. It is made of metal. The metal must not be heavy but it must be very strong. There is gas inside the rocket which is made very hot. When it rushes out of the end of the rocket, the rocket is pushed up into the air.
Rockets can fly fat out into space. Rockets with men inside them have already reached the moon. Several rockets, without men inside them, have been sent to other worlds much farther away. One day rockets may be able to go anywhere in the space.
4. Which of the following statements about a rocket is NOT true?
A) It can fly when there is no air.
B) It can fly without wings.
C) It is made of strong metal.
D) It is propelled by burning gas inside it.
5. A rocket is pushed up into the air when
A) hot gas rushes out of its head.
B) it is powered by gas.
C) hot gas rushes out of its bottom.
D) hot gas rushes out of its neck.
Keys: DADDC
十道必看的GRE数学易错题
GRE考试数学部分的题型解析与解题技巧
备考真经:GRE数学难点及解决方法
GRE数学考试备考经验技巧
2011GRE考试选择题精炼(2)
真题汇总:11月27日gre数学真题部分
2014新GRE数学基本概念总结
GRE数学难题总结(五)
2011GRE考试选择题精炼(1)
gre数学词汇大全——有关代数式、方程和不等式
GRE数学:网络课堂逻辑笔记(2)
GRE数学:网络课堂逻辑笔记(6)
GRE数学部分常用策略
新GRE数学中的难点及解惑
GRE数学运算词汇汇总
GRE数学基本概念15条你都掌握了吗
GRE数学部分读不懂题怎么办
GRE数学代数式、方程和不等式词汇大全
GRE数学难题总结(一)
真题汇总:11月19日gre数学真题部分
新GRE数学高频专业术语汇总
GRE数学复习几个注意地方
GRE数学考试难点及解决方法
gre数学考试常用知识1:数理统计
GRE数学考题总结--几何
GRE数学答题常用策略
GRE数学考试复习时的五点注意事项
GRE数学考试部分术语总汇——代数部分
最新gre考试数学知识排列组合篇习题
GRE数学考试部分术语总汇——几何部分及其它
不限 |
英语教案 |
英语课件 |
英语试题 |
不限 |
不限 |
上册 |
下册 |
不限 |