变化

Heating or cooling a substance may cause changes that can be observed. Sometimes these changes are reversible, and sometimes they are not.

::加热或冷却一种物质可能会引起可以观察到的变化。这些变化有时是可逆的，有时则不然。

Bang...the car door slams shut. Suddenly, you realize you left your book bag inside the car. "Oh no." you think, "The car door is locked." You run inside and get the car key. "Beep, Beep," goes the car as the door lock clicks open. You quickly grab your bag and run inside.

Lucky for us, some things are not permanent. Car doors can be closed and reopened. Car doors can be locked and unlocked. Are all changes able to be undone? Are they reversible?

::爆炸……车门砰的一声关上了。突然，你意识到你把书包忘在车里了。“哦，不，”你想，“车门是锁着的。”你跑进去拿车钥匙。“嘟嘟，嘟嘟，”当门锁咔哒一声打开时，汽车发出声音。你赶紧拿起包跑了进去。幸运的是，有些事情不是永久的。车门可以关闭和重新打开。车门可以锁和解锁。是否所有更改都可以撤消？是可逆的吗？

Water is normally a liquid at room temperature. It turns to a solid when it gets colder. We call this solid, ice. Ice forms at zero degrees (0°C). We call this change, freezing. You may see lakes freeze. Where else might water freeze?

Animals need liquid water. Water can turn back into a liquid. It does this when it warms up.

::水在室温下通常是液体。温度越低，它就变成固体。我们称这种固体为冰。冰在摄氏零度形成。我们称这种变化为冻结。你可能会看到湖泊结冰。水还会在哪里结冰呢？动物需要液态水。水可以变回液体。当它变暖的时候就会这样。

You buy some ice cream at the store. It is half melted when you get home. You quickly place it in the refrigerator. That night you enjoy a nice bowl of ice cream with your family. Melting ice cream is a reversible change. Can you think of other things that melt?

::你在商店买了一些冰淇淋。当你回到家时，它已经融化了一半。你很快把它放进冰箱。那天晚上，你和家人一起享用了一碗美味的冰淇淋。冰淇淋融化是一个可逆的变化。你还能想到其他会融化的东西吗？

Some changes are permanent. They cannot be changed back. Cooked foods cannot be changed back. Once you cook a raw egg, it cannot become raw again. Once you boil a carrot, it will not become crisp again. Even if you cool the carrot, it will not change back.

::有些变化是永久性的。不能再改回去了。煮熟的食物不能换回来。生鸡蛋一旦煮熟，就不能再生了。胡萝卜一旦煮熟，就不会再变脆了。即使你把胡萝卜凉了，它也不会变回来。

In many areas, scientists burn areas of forest. Fire brings change. Are forest fires bad?

Fire can benefit the forest. Dead trees get burned. This leaves room for new growth. New trees and plants grow where older trees once were. The new growth provides food for the animals. In some ways, fire gives a forest new life.

::在许多地区，科学家焚烧森林。火带来变化。森林火灾不好吗？火对森林有益。枯树会被烧掉。这为新的增长留下了空间。新的树木和植物在老树生长的地方生长。新生长的植物为动物提供了食物。在某些方面，火赋予了森林新的生命。

For things that are burned, they do not come back to life. For the burned trees, the change is permanent. When trees are burned, they are turned to ash. The ash cannot be turned back into a tree. This change is not reversible. For the forest, the change can be positive. Changes can be permanent or not permanent. That does not mean either one is good or bad.

Change is all around us. Change brings new things. Some things are reversible. Some are not. Can you name some changes? Are they reversible or not reversible?

::因为燃烧的东西不能再复活。对于被烧毁的树木来说，这种变化是永久性的。当树木被烧毁时，它们就变成了灰烬。灰烬不能再变成树了。这种变化是不可逆转的。对森林来说，这种变化可能是积极的。变化可以是永久性的，也可以不是永久性的。这并不意味着一个人是好是坏。变化就在我们身边。变化带来新事物。有些事情是可逆的。有些则不然。你能说出一些变化吗？它们是可逆的还是不可逆的？