STEM Experiment: Make Your Own Bouncy Balls

Education |  3 min. read

If your kids think that the idea of a STEM experiment, learning about polymers, sounds like life before Snapchat (aka, boring!), then we’ve got a word for you:  Boing!

Yep, we’ve got a DIY bouncy ball project for you (courtesy of the scientists who work in the Fun Department at Valero).  It’s quick too, so your kids will be out of the “lab” and into bouncing their new ball off the floor, the wall, the ceiling, in no time.

Here’s what you’ll need: 

  • White school glue (for a lot of us, that’d be Elmer’s – but any white glue will work) – 1 tablespoon.
  • Food coloring (you choose).
  • Borax powder (if you don’t have any already in the house, you can find it at almost any hardware store, grocery store (in the laundry detergent aisle), or those really big stores) – 1/2 teaspoon.
  • Cornstarch – 3 tablespoons.
  • Warm water – 4 tablespoons.
  • 2 cups (for mixing in) – small ones will do.

Here’s what you’ll do:

  • Mix the cornstarch, borax and warm water in cup #1.
  • Mix the glue and food coloring in cup #2.
  • Pour cup #1 into cup #2.
  • Stir, stir, stir until a slimy glob forms in the middle of the cup (But don’t stop yet! We’re not making slime today.)
  • Take the glob out of the cup (There will be some extra liquid left in the cup. That’s fine.) and roll it in your hands into a ball (it will be stretchy and stringy at first, then it comes together).  If it’s still a little wet, dry it with a paper towel.
  • And Boing! It’s a ball.

If you’d like to watch all that being done, before trying it yourself, here you go:  DIY Bouncy Ball.

The science of all that?  

A “polymer” is something made up of long chains of big molecules – in this case, the main ingredient of the glue, polyvinyl acetate (PVAc).  Those molecule “chains” can slide past each other, so you can pour the glue out of the bottle. 

That PVAc is the result of a couple chemistry reactions that begin with the petrochemical ethylene.  The ethylene is used to make a monomer called vinyl acetate, and that vinyl acetate is converted to POLYvinyl acetate (see what we did there?).

Chemistry tip: just add “poly” to the front of the monomer name and you have the polymer name.

But add borax to the polymer glue and you get slime, a sort of liquid, sort of solid.  That’s because the borax “ties” those big molecules together (a scientist would call that “cross-linking”) so they don’t slide anymore, they squish and squash.

Now add cornstarch, and you’re entering non-Newtonian fluid territory (very sciency stuff here).  The result?  Even more solid now, and less gooey – so you can form your slime into a ball.

And that same polymer principle (long, connected chains of molecules) is behind the many plastics we use every day – from the plastic used to make milk jugs, to the polymer fiber in outdoor rugs, to the plastics in our phone casing and keyboard, to the carbon fiber-reinforced plastics that airplanes and cars and bikes are built from.

Product                        Monomer                                            Polymer                       

Milk Jug                        ethylene                                              polyethylene

Outdoor Rug               propylene                                             polypropylene

Phones                          acrylonitrile-butadiene                     poly (acrylonitrile-butadiene-styrene)

Carbon Fiber               acrylonitrile                                         polyacrylonitrile