Use chemistry to make a bouncing polymer ball, then alter the procedure to see the effect the changes have on the characteristics of the ball.
Bouncy Polymer Balls - Ivy's Chemistry Blog
Bouncing Polymer Ball - CuriOdyssey
What Makes a Ball Super?
Best Recipe for DIY Bouncy Balls!
How to Make Bouncy Balls Experiment
DIY Borax Bouncy Ball -Experiment - Go Science Girls
Crafts 4 Camp: August 2013
Make a bouncy ball! : Fizzics Education
How to Make Bouncy Balls - The Stem Laboratory
How to Make a Bouncing Polymer Ball