Polymer Bouncy Balls

Introduction
Balls have been toys practically forever, but the bouncing ball is a more recent innovation. Bouncing balls were originally made of natural rubber, though now bouncing balls can be made of plastics and other polymers or even treated leather. You can use chemistry to make your own bouncing ball. Once you understand the basic technique, you can alter the recipe for the ball to see how the chemical composition affects the bounciness of the ball, as well as other characteristics.
The bouncing ball in this activity is made from a polymer. Polymers are molecules made up of repeating chemical units. Glue contains the polymer polyvinyl acetate (PVA), which cross-links to itself when reacted with borax.
Bouncing Polymer Ball Materials
Here's a list of materials you need to gather to make bouncing polymer balls:

• borax (found in the laundry section of the store)
• cornstarch (found in the baking section of the store)
• white glue (e.g., Elmer's glue - makes an opaque ball) or blue or clear school glue (makes a translucent ball)
• warm water
• food coloring (optional)
• measuring spoons
• spoon or craft stick to stir the mixture
• 2 small plastic cups or other containers for mixing
• marking pen
• watch with a second hand
• metric ruler
• zip-lock plastic baggie 

Procedure

1. Label one cup 'Borax Solution' and the other cup 'Ball Mixture'.
2. Pour 2 tablespoons warm water and 1/2 teaspoon borax powder into the cup labeled 'Borax Solution'. Stir the mixture to dissolve the borax. Add food coloring, if desired.
3. Pour 1 tablespoon of glue into the cup labeled 'Ball Mixture'. Add 1/2 teaspoon of the borax solution you just made and 1 tablespoon of cornstarch. Do not stir. Allow the ingredients to interact on their own for 10-15 seconds and then stir them together to fully mix. Once the mixture becomes impossible to stir, take it out of the cup and start molding the ball with your hands.
4. The ball will start out sticky and messy, but will solidify as you knead it.
5. Once the ball is less sticky, go ahead and bounce it!
6. You can store your plastic ball in a sealed ziploc bag when you are finished playing with it.
7. Don't eat the materials used to make the ball or the ball itself. Wash your work area, utensils, and hands when you have completed this activity. 

Things to Try with Bouncing Polymer Balls If you use the scientific method, you make observations before experimenting and forming or testing a hypothesis. You've followed a procedure to make a bouncing ball. Now you can vary the procedure and use your observations to make predictions about the effects of the changes.

• Observations you can make and then compare as you change the composition of the ball include the diameter of the finished ball, how sticky it is, how long it takes to solidify into a ball, and how high it bounces.
• Experiment with the ratio between the amounts of glue, cornstarch, and borax. Adding more cornstarch will make a ball that stretches and bends. Using less borax will produce a 'goopier' type of ball. Add more glue for a slimier ball.