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Learning about changes that can be undone to get the original material back.
Have you ever built a tower of blocks and knocked it down, only to build it again? What if everything in the world had a secret 'undo' button like a computer?
Imagine you are playing with a piece of modeling clay. You squish it into a ball, then you stretch it into a long snake. Can you turn it back into a ball? Yes! This is called a reversible change. A reversible change is like a two-way street. You can go forward to change the material, and you can go backward to get the original material back. In these changes, we don't make a brand new material; we just change how it looks or feels for a little while. If you can 'undo' it, it is reversible!
Quick Check
If you put on a pair of socks and then take them off, is that a reversible change?
Answer
Yes, because your feet and the socks go back to exactly how they were before!
Water is a master of the 'undo' button! When water gets very cold, below , it turns into solid ice. If we take that ice out of the freezer and let it warm up, it turns back into liquid water. We can do this over and over again! Many things work this way. Chocolate can melt into a gooey liquid when it's warm, but if you put it in the fridge, it becomes a solid bar again. The material stays the same—it is still chocolate—it just changed its shape and hardness.
1. Take 1 solid ice cube from the freezer. 2. Place it in a warm bowl and watch it turn into liquid water. 3. Pour that liquid water back into the ice tray. 4. Put it back in the freezer to get your solid ice cube back!
Quick Check
Is melting a candle wax a reversible change?
Answer
Yes, because when the wax cools down, it turns back into solid wax.
Sometimes a change looks like magic. If you stir a spoonful of sugar into a glass of water, the sugar seems to disappear! This is called dissolving. Even though you can't see the sugar, it is still there—you can taste it! To 'undo' this change, you can leave the glass in a sunny spot. The water will slowly turn into vapor and disappear into the air, leaving the solid sugar crystals at the bottom of the glass. You found the sugar again!
1. Mix of salt into a cup of water until you can't see the grains. 2. Pour the water onto a flat plate. 3. Wait for the water to evaporate (dry up). 4. Look at the white crystals left on the plate—that is your salt!
How can you tell if a change is reversible? You have to be a science detective! Ask yourself: 'Is the material still the same stuff?' If you fold a piece of paper into a plane, it is still paper. You can unfold it. If you mix sand and water, you can use a filter to catch the sand. These are reversible. But be careful! If you bake a cake or burn a piece of wood, you can never get the flour or the log back. Those are not reversible!
Imagine you mix a bucket of blue LEGO bricks and red LEGO bricks together. 1. The change is 'mixing' the colors. 2. To reverse it, you simply pick out the red ones and put them in a separate pile. 3. Because you can separate them back to how they were, mixing the bricks is a reversible change!
Which of these is a reversible change?
What happens to water when it reaches ?
Folding a piece of paper is a reversible change.
Review Tomorrow
Tomorrow morning, look at your breakfast. Can you find one thing that has changed in a way that can be undone?
Practice Activity
With an adult, melt a small piece of butter in a pan, then pour it into a small dish and put it in the fridge. Check it after 30 minutes to see if it changed back!