Close-up Look at Change

Ask students summarize what they have heard about the classic story of the Three Little Pigs. Have students summarize the what they recall of the story. Be sure to mention that the pigs built increasingly sturdy structures because the wolf kept blowing their houses down!

Ask students to stack up a few miscellaneous objects on their desk and then knock them over in any way they choose (bumping table, blowing them down, and so on).

Have them turn and talk to consider whether the change they set in motion was a physical or a chemical change.

Answer:

Physical

The story is prepared as an interactive reading activity for students to read individually or in small groups, using a tablet or computer.

​

Or teachers may opt to project the story to make it a whole-class activity.

The story is "interrupted" with five questions students answer in order to continue. Copies of the questions and answers are shown on the right.

The questions on the right may be used as an assessment or to prompt a class discussion.

Sample responses:

In your own words, explain the difference between physical change and chemical change. Give an example of each from the story.

• A physical change is when something stays the same substance, but it changes form. So if an object is broken or torn, like the straw lab in the story, that’s just a physical change. But if a substance changes, down at the level of how its atoms are stuck together, then it’s a physical change. When the wood lab burns, that’s an example of a chemical change, because the wood changes so that it’s not wood anymore.

Do mixtures always have to be in liquid form? Are there any examples in the story to help explain what a mixture is?

• Lots of mixtures are liquid, but they don’t have to be. Concrete would be a mixture, because it’s got pebbles in it, but also cement holding it together. The bricks in the story are like that. They’re made with baked clay but with sand mixed in, and maybe lime. If you look very closely at a brick, you can see different substances. And they don’t have to be combined in exact proportions.

If you could explain lighter-than-air travel to the wolf, how would you explain it?

• The air inside a hot air balloon expands when it gets hot, so some of it gets pushed out of the bottom of the balloon. That means there is less air inside the balloon, and that makes it less dense than the air outside. So it floats up, kind of like a bubble floats up in water. And it’s so much less dense that it can lift the basket and passengers, even though they’re heavier than air.