Did you know you can make your own bouncy balls at home? You can with this project that's also a quick chemistry exploration in polymers. You'll be jumping for joy right alongside your super awesome bouncy balls at the end of this experiment.
Borax (sodium tetraborate) is a naturally-occurring mineral salt commonly used as a laundry booster or cleaner. As with any other cleaning product, it should be kept away from children not under direct supervision of an adult. Do not allow children to ingest Borax. If consumed, contact a poison control center immediately.
Make your glue mixture. In the second cup, add 1 tablespoon of cornstarch, and 1 tablespoon of glue. Add in a few drops of your desired food coloring and mix them all together with another mixing stick.
Mix the two until it forms a blob around the stick. Don't worry if there's liquid left in the cups! Let the blob sit in the cup for about another minute.
Test out your new creation! How high can you bounce your handmade bouncy ball?
Note that you shouldn't expect these balls to bounce as high as a rubber ball you buy from the store. We also found that different glues behave pretty differently, so if you want to keep experimenting you can try different amounts of glue, borax, and cornstarch to see which will give you the best bounce.
Be careful not to bounce your ball on carpet or fabrics as they may stick. The ball will dry and get hard if you leave it out. If you put it in a plastic bag or air-tight container, it will keep for about a week.
What's going on?
The glue you used contains some super-long molecules called polymers. In the glue, these polymers are free to float around without getting tangled up with each other. But when you added the borax, that caused a chemical reaction to take place. That reaction caused the long polymer molecules to stick to each other. This makes it impossible for the molecules to slide past each other, and that's what turns the liquid glue into a bouncy ball. This type of reaction is called cross-linking. Real rubber balls also get their bounce from cross-linked polymers!