Silly Putty can be squeezed, molded, bounced like a ball, imprinted on books, dropped, rolled, and some scientists even use it to model glaciers! How can one material do so much??
Silly Putty belongs to a class of materials called viscoelastic—a combination of "viscous" and "elastic." Read on to learn how you can make your own version of this simple yet magical toy!
- 1/2 cup all-purpose glue
- 1 tsp borax
- water
- food coloring (optional)
- measuring cup
- spoon
- small mixing bowls
- plastic baggie for storage
Mix together ½ cup of glue and ½ cup of water. Add food coloring to achieve your desired color. Stir until everything is nicely combined and there are no more big lumps.
Dissolve 1 teaspoon of borax into ½ cup hot water. Stir until you can no longer see the borax crystals.
Pour the borax mixture into the glue+water mixture and stir.
Keep stirring! After a little bit the mixture will start to firm up.
Once your mixture starts to get firmer, pick it up and start shaping it into a ball. Now you have your very own putty!
Investigate the material properties of your putty!
- Take some of your putty and roll it into a ball. What happens when you drop it onto a hard surface? What about if you drop it out the window? (Make sure no one is standing below you!)
- Take your ball and stretch it. What happens to the stretched-out putty when you drop it onto a hard surface?
- Make another ball with your putty. What happens when you pull it apart slowly? What about if you rip it apart quickly?
- Roll a ball of putty and leave it on a flat surface. What happens after you have left it for awhile?
These experiments showcase the viscoelastic properties of Silly Putty. This means there are some situations where the putty is viscous like a thick fluid (see What is Viscosity?) and others where it is elastic like a bouncy solid. Can you figure out which conditions lead to which behavior?
More ways to investigate your putty:
- There are many recipes online for making Silly Putty/Flubber. They have slightly different ratios of glue/water/borax, so feel free to try other recipes and see how the behavior changes.
- What happens to your putty if you only stir the borax and glue mixtures for a short amount of time? For a longer amount of time? Why do you think the amount of stirring might affect the properties of your putty?
- Although glaciers are definitely not funsized objects, you can use your funsize putty to model the flow of glaciers! Check out this activity from the National Park Service.
The way a viscoelastic material behaves depends on how we interact with it. When you apply a s-l-o-w force to the Silly Putty, e.g. by pulling it, it will exhibit viscous behavior, stretching and even flowing like a sticky fluid. On the other hand, when you apply a rapid force, e.g. by punching it or throwing it against a hard surface, it will behave elastically, deforming and springing back like a solid. (To learn about other viscoelastic materials, see Ketchup and Oobleck and Slime, Oh My!)
The secret is cross-linked polymers! Polymers are long chain molecules made of smaller repeating units. Commercial Silly Putty uses silicone (with an e!), a type of polymer with a backbone of alternating silicon and oxygen atoms. Our homemade version uses all-purpose glue, which is a polymer of polyvinyl acetate. In both cases, the element boron in the borax binds to the polymer chains, cross-linking them to create the putty you know and love.