Hi. Today, we made bouncy balls in our Chemistry lab and tested their bounciness to see which group could get the best recipe. A “good” bouncy ball would have a rather smooth texture, would hold its shape well, would bounce high, and would also have a high bounce-to-mass ratio.
(Let it be known that “today” was still 1/10/14 when I posted this.)
Ingredients and Materials: poly-vinyl-acetate (glue) and sodium borate (borax). When mixed, they are supposed to polymerize and the glue is supposed to turn into a solid, dry mass with enough rolling or molding into a ball. Mixed together in plastic cups and bowls; borax solution measured with plastic pipettes.
Procedure: My group first tested the first mixture of 10 grams of glue, an borax/water mixture of 1:1, and 1 mL of water added to the glue. It failed and we decided to try a borax concentration of 2:1. We decided to double the amount of borax put into the glue because the glue wasn’t even really solidifying at all, and it wouldn’t keep its shape and bounce well if it wasn’t fully polymerized by the borax. This second mixture was very hollow with only the outer skin of glue solidified so we have to tear the whole thing up to form evenly, and this made it very sticky at first, but it eventually gained a shape as I rolled it into a ball, and we eventually got it to dry out and solidify a bit. We bounced it on the floor a few times to see how high it would bounce, but we decided to restart again and try using 10g of glue, the 2:1 borax solution, and 2 mL of the solution instead of 1.
This third mixture took shape very quickly upon mixing, lost its outer stickiness very fast, and still bounced as good as the other one, so it seemed to be the best proportion of ingredients to us. Besides the obvious fact that a smaller proportion of borax to glue would leave the glue a liquid, I think it was little more than luck that we managed to find such good proportions on virtually our second try. I think the method we used mattered because if we didn’t tear the ball apart at first, it probably would’ve stayed hollow in the middle and smash upon impact and fail.
Anyways, we used two more bouncy balls of this mix for our final product, and we also managed to get some good words for the texture and consistency of their weight when the time came for our class’s bounce-height contest.
Results: Each team’s set of bouncy balls was both weighed and then dropped from a height of 1 meter and three or four judges determined how high up it returned.
Ball 1: 10.3 g, bounced to a height of 41cm, 42.5cm, and 44cm.
Ball 2: 10.2 g, bounced to a height of 46cm, 46cm, and 44cm.
I don’t know what else to talk about, so that’s all I have to say for now.