Changes

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

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?

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.

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?

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.

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.

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?