Changing Matter. Matter can change.
改变物质。物质可以改变。
If you cut paper into pieces, it looks different.
如果你把纸切成碎片，它看起来就不一样了。
But each piece of paper is still paper.
但每张纸仍然是纸。
This is a physical change.
这是物理变化。
A physical change means the matter has changed from what it looked like, but it is still the same matter.
物理变化意味着物质已经从它看起来的样子发生了变化，但它仍然是同一个物质。
If you stir salt into water, the salt will dissolve.
如果你把盐搅到水里，盐就会溶解。
You cannot see it anymore.
你再也看不到它了。
Salt dissolving in water is a physical change.
盐溶于水是一种物理变化。
When all the water evaporates, the salt will be all that is left.
当所有的水蒸发后，剩下的就只有盐了。
You can separate salt from water this way.
你可以这样把盐和水分开。
If you burn paper, smoke and ash are made.
如果你烧纸，就会产生烟和灰。
Smoke and ash are not paper.
烟和灰不是纸。
This is a chemical change.
这是化学变化。
A chemical change means new matter is made.
化学变化意味着新物质的产生。
The metal iron can rust.
金属铁会生锈。
Rusting is a chemical change.
生锈是一种化学变化。
Parts of iron change into new matter, which is not iron.
部分铁变成新物质，而新物质不是铁。