Yummy Science – Custard Bouncing Balls. Experiments you can try in the kitchen – Magical Water, Growing Crystals, Spud Guns, Designer Onions, Honeycomb Toffee, Sticky Milk, Toast Busters, Toasty Science, Self Slicing Banana, Secret Messages

How it's done

We tried this experiment with Northsound1, listen to the results:

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Photos

Science Links

All about polymers from National Geographic
or visit the Polymer Science Learning Centre
for a bit of fun… what happens when you try a BIG experiment?

Other links:

More fun nutrition activities at
the Rowett Research Institute, eduweb
Check out National Science & Engineering Week at:
The BA (British Association for the Advancement of Science)

Further food science ideas for the primary aged audience are presented in the ‘Food for Thought resource, downloadable at The BA

For secondary pupils, there are lots of great kitchen chemistry ideas available in the Salters Chemistry Club handbooks or in various publications produced by the Royal Society of Chemistry

Exploring the science:

PVA (polyvinyl acetate) is a polymer or ‘long chained molecule’ - so too is starch (present in the custard powder). The borax causes cross-links to develop between the two polymers and the mixture becomes stiff. It is important to get the correct amount of borax, too much i.e. too many cross-links, and the mixture is brittle; too little and the mixture flows; just right and the mixture can be rolled into a ball and bounced! Polymers (like PVA and starch) are a very important part of our world.

Taking it further:

Dilute the borax solution by adding a liitle more water and instead of bouncy balls you can make ‘silly putty’ - when it is pulled slowly will stretch, pulled quickly and it will snap.
Experiment with varying the proportions of the ingredients to investigate what sort of material you get.

Custard balls that bounce just like hard rubber balls ?! Yes it’s really possible, simply follow the instructions below …

You’ll need:

Household Borax (you can get it from a pharmacy)
PVA glue
Water
Custard powder (or if you prefer use cornflour and a food colouring of your choice)
Tablespoon
Teaspoon
2 cups/containers

What to do:

Make a borax solution by adding 1 teaspoon of borax to 2 tablespoons of warm water, stir to dissolve.
In another container mix one tablespoon of PVA glue with 2 teaspoons of custard powder.
Add one teaspoon of your borax solution to the custard/PVA mixture and stir well.
The mixture will become stiff - tip it out of the cup and knead well with your hands.
Roll into a ball.

What happens:

The ingredients combine to make a fairly solid mixture which when rolled into a ball, you should be able to throw and bounce!