Re: how would you increase the bounciness of a polymer

Dear Mary,
   Once you have selected a polymer material there is nothing that can be 
done to increase the bounciness except alter its chemical composition or 
change the number of chemical bonds between the polymer molecules. Doing 
this requires advanced methods and reagents. It is too difficult for a 
science fair. However, I write three ideas for you, and here they are:

1. A ball bounces best on a very hard surface like a concrete driveway, 
less well on soft earth or grass, and not at all, or very little on a soft 
pillow. A possible project would be to demonstrate the effect of the other 
surfaces on the bouncing of a solid rubber ball. The effect can be 
explained with the help of physics. (Dan Berger adds: this effect is called 
"elasticity." Look up "elastic collisions.")

2. Secondly, balls that require 
inflation bounce best with the correct air pressure. Think of a "flat" 
basketball. What a poor bouncing thing. Adding air at first only shapes it 
up without much increase in bounciness. After the basketball is rounded 
out each little increase in pressure stretches the polymer shell itself, 
and the ball's bouncing improves until the correct pressure is reached. 
Further increases in pressure may stretch the polymer too much and the ball
may burst. So stretching the polymer improves bouncing. It's like 
stretching a rubber band. You could mount rubber bands between nails that 
are set at various distances and demonstrate the increase in their 
response to sideways pulling. (DB: be sure to use identical rubber bands!)

3. Suppose you have three identical solid 
rubber balls. You can age two of them in an oven set at 170 degrees F for 
2 hours and 10 hours. Then compare the bouncing of all three. In the oven 
some of the polymer molecules will be changed and the bounciness may be 
changed. I hope this helps.