Rusting is a chemical change. Rusting is like burning. Rusting joins iron to oxygen. Rusting is a slow chemical change. Burning is a fast chemical change. An orange ripening on a tree is a slow chemical change.
All matter is changing. Some changes happen slowly. Some changes happen fast. It takes a long time for mountains to change. A forest fire can change the trees very fast.
Vocabulary 词汇
grind [ɡraind] vt. & vi. 磨碎、嚼碎；
vt. 旋转开动、压迫；
n. 磨、碾、苦差事
molecule ["m？likju：l] n. 分子
dust [d？st] n. 灰尘、尘土、尘埃、遗骸；
vt. & vi. 拂（一拂）、掸（一掸）
tiny ["taini] adj. 极小的、微小的
microscope ["maikr？sk？up] n. 显微镜
substance ["s？bst？ns] n. 物质、主旨、要旨、实质、本体
clay [klei] n. 黏土、泥土
mold [m？uld] n. 模子、铸型；
vt. 浇铸、塑造
cereal ["si？ri？l] n. 谷类植物、谷物、麦片粥
digest [dai"d？est] vt. & vi. 消化；
vt. 透彻了解；
n. 摘要、文摘、汇编
baking ["beiki？] n. 烘焙、一次烘焙的量
spoil [sp？il] vi. 变质；
vt. 损坏、毁掉、溺爱、宠坏
oxygen ["？ksid？？n] n. 〈化〉氧、氧气
rusting ["r？sti？] n. 生锈
ripen ["raip？n] vt. & vi. 成熟、使熟
Practice
I. Write the answer in the blank using the correct word.
1．A change in size or shape is a ．
2．Burning and rusting are examples of a ．
3．When matter gets hot its goes up．
4．All matter is made of a． and b． that are too tiny to see with a microscope．
5． change makes new matter from old matter．
II. Write P for physical change. Write C for chemical change.
1．breaking a window
2．melting ice cream in a cone
3．digesting your food
4．smashing a piece of clay
5．a forest fire
6．jumping up and down
7．a mud puddle drying out
8．the spoiling of food
译文
物质可以有多小呢？你可以把石头敲成许多块碎片，你可以把一块糖研磨成粉末，但你能制成的最小的东西是什么呢？科学家们把最小的物质叫做原子和分子。数以百万计的分子可以构成极其细微的尘埃。即便是倍数最高的显微镜，也不能看到原子和分子。所有事物都是由微小的原子和分子构成。
你可以加热物体，冷却物体，打碎物体，你可以改变物体的大小和形状，所有这些变化都是物理变化。物理变化不会把一种物质变成另一种物质。粘土仍然是粘土，即使它被铸造成型。糖依然是糖，即使你把它放在你的麦片粥里，糖没有变成盐。物理变化仅仅改变了物质的形状和大小。
并非所有的变化都是物理变化。有时候，当事物变化时，新事物产生了。这个新事物看起来和旧事物不一样，表现得也和旧事物不一样，这种变化叫做化学变化。
许多化学变化是有益的。你吃的食物会发生化学变化，当你消化食物时，你的身体让它们产生化学变化。当你消化时，你吃的食物已不再是食物。你的身体需要改变这些食物，然后来使用它。消化了的食物可以给你的身体提供能量。生长中的植物显示出的就是一种化学变化，从土壤和空气中得来的食品和水被转化成植物细胞。这些化学变化都是有益的化学变化，是新事物从旧事物中形成。
当两种物体混合时，可能会发生化学变化。烘焙蛋糕就是一种化学变化，不同种类的物质混合在一起，使蛋糕变成了烤蛋糕。旧物质在一起以新的方式组合，产生了新事物。
其他一些化学变化可能没那么有用。当食物存放时间过长时，会变质。当食物变质时，发生的是化学变化。火也是一种化学变化，森林火灾不是一个有益的化学变化，但是那些让你的房间变温暖的火是有益的化学变化。燃烧可以是有益的或无益的，它是一种化学变化，因为它让一些物质和氧气联结在一起。
生锈是一种化学变化。生锈和燃烧一样，让铁和氧气相结合。锈蚀是一个缓慢的化学变化，燃烧是一种快速的化学变化，橙子在树上成熟是一个缓慢的化学变化。
所有的事物都在发生变化，一些变化产生得非常缓慢，一些变化发生得很快。山脉改变需要长长的一段时间，而森林火灾则可以非常快地改变树木。
练习
Ⅰ.用正确的单词填空。
1．大小和形状改变的变化是 。
2．燃烧和生锈是 的例子。
3．当事物得到热量时 会升高。
4．所有的物质都是有 和 构成，它们太微小了以至于用显微镜都看不到。
5． 变化可以把旧物质变成新物质。
Ⅱ. 判断下列各种变化，若是物理变化就写P，化学变化写C。
1．打破窗户 2．锥形冰激凌融化 3．消化食物
4．砸碎一块粘土 5．森林火灾 6．往上往下跳
7．泥水坑干涸 8．食物变质
Ⅰ．1．physical change 物理变化
2．chemical change 化学变化
3．temperature 温度
4．a．atoms 原子 b．molecules 分子
5．Chemical 化学的
Ⅱ．1．P 2．P 3．C 4．P 5．C 6．P 7．P 8．C
03 Solar System 太阳系
The sun， earth， moon， planets， and smaller objects called meteoroids， comets， and asteroids， make up what we call the solar system. He had made the stars， also.
Sun. Our sun is a star. It is the center of our solar system. The earth， moon， planets， and smaller heavenly bodies revolve around the sun. Without the sun， life on this planet earth would be impossible. Without the sun there could be no weather. The tilt of the earth causes our seasons. The heat from the sun moves the air causing the wind. The sun seems to rise in the east and set in the west because of the rotation of the earth. The earth rotates once every twenty-four hours on its axis. The revolution of the earth around the sun occurs once every 365.14 days. Our year is measured by this revolution. The sun also moves. It spins on its axis and rushes through the Milky Way at a speed of 43，000 miles （69，187 kilometers） an hour.
Moon. Our nearest neighbor in space， the moon， is about 240，000 miles （386，160 kilometers） from the earth. Since the moon has no air or water， no life is there. The gravity on the surface of the moon is only about one-sixth of that on the earth. If a person weighs sixty pounds here on earth， he would weigh only ten pounds on the moon. If he could lift fifty pounds here， he could lift three hundred pounds there. Two astronauts made the first landing on the moon in 1969. They brought back samples of soil and rocks for study.
Planets. Do you remember how many planets are revolving around the sun？ Nine planets， including the earth， orbit the sun. You will recall that Mercury is the nearest to the sun. The other planets， in order from the sun， are Venus， Earth， Mars， Jupiter， Saturn， Uranus， Neptune， and Pluto. （For twenty years at a time Pluto is closer to the sun than Neptune.）
Stars. The number of stars that we can see on a clear night without a telescope is between three thousand and five thousand. Man has estimated an endless number of galaxies with billions and billions of stars in each galaxy.
Because stars have been studied for centuries by astronomers， some people confuse astronomy and astrology. Astronomy is a scientific study of the universe. Astronomy is a true science. Astrology is superstition. Astrologers make a business of trying to tell people’s fortunes by studying the planets and stars. The Bible warns against believing in astrology. Scientists know that such dependence on the stars is nonsense. We study astronomy to better understand the universe， not to learn about ourselves or our future.
Vocabulary 词汇
meteoroid ["mi：tj？r？id] n. 流星体
comet ["k？mit] n. 彗星
asteroid ["？st？r？id] n. （尤指火星和木星轨道间运行的）小行星
rotation [r？u"tei？n] n. 旋转、转动、转、轮流、轮换
axis ["？ksis] n. 轴、轴线、中心线、坐标轴、基准线
spin [spin] vt. & vi. 使……旋转；
vt. 杜撰
Milky Way 银河
astronauts ["？str？n？：t] n. 宇航员、太空人
orbit ["？：bit] n. 轨道；
vt. & vi. 在……轨道上运行、环绕轨道运行
Venus ["vi：n？s] n. 金星、维纳斯
Mars [mɑ：z] n. 火星
Jupiter ["d？u：pit？] n. 〈天〉木星
Saturn ["s？t？n] n. 〈天〉土星
Uranus ["ju：？r？n？s] n. 天王星
Neptune ["neptju：n] n. 海王星
Pluto ["plu：t？u] n. 冥王星、阴间的神
telescope ["telisk？up] n. 望远镜；
vt. & vi.（使某物）变短（叠缩在一起）、嵌入
confuse [k？n"fju：z] vt. 使困惑、把……弄糊涂、混淆、把……混同、混乱
astronomy [？s"tr？n？mi] n. 天文学
astrology [？s"tr？l？d？i] n. 占星术
superstition ["sju：p？"sti？？n] n. 迷信、迷信行为
Practice
Write true or false.
1．The earth revolves around the sun causing day and night．
2．The sun travels through the Milky Way at high speed．
3．Without the sun， life on earth would be impossible．
4．Nine planets orbit the sun．
5．Four planets orbit the earth．
6．Astrology is a superstition warned against in the Bible．
7．The earth is the center of the solar system．
8．Comets are smaller objects in space that orbit the sun．
9．Asteroids orbit the moon once every twenty-four hours．
Write the letter of the correct answer on each line.
1．Two astronauts landed on the moon in ．