Silly Putty Lesson

Silly Putty at a glance

Background

If you have played with Silly Putty®, you know how fun it can be! It can bounce like a rubber ball, break by tearing it apart, be stretched, and will flow into a puddle after a period of time. If you flatten it and press it over a comic or newspaper print, it will copy the image to the putty.

So how in the world can it do so many things? Is it a solid or is it a liquid? The most important compound in Silly Putty® is polydimethylsiloxane (PDMS). This is the simplest member of the polymer family known as the silicones.

This experiment will demonstrate how each of the components of Silly Putty® play a role in its formation.

Lesson Objective

To demonstrate the unique property of time-dependent strain behavior in viscoelastic materials using Silly Putty®. To demonstrate the different responses of Silly Putty® when stretching it at different speeds.

Experiment Description

This experiment will explore the physical properties of non-Newtonian fluids like Silly Putty®. Students will be tasked with exploring how the rate of stretching, pulling, and squeezing Silly Putty® influences its mechanical response. Silly Putty® can be cooled to explore fracture.

Materials List

Items provided in the kit:
- Silly Putty® (for demonstration)
Items to be supplies by teacher/school:
- Additional Silly Putty® (for students to follow along)
Optional:
- Play Doh for comparison

Safety Precautions

Silly Putty® is a choking hazard:

Do not allow children to put Silly Putty® in their mouths or attempt to swallow it.
Silly Putty® is non-toxic but should not be ingested.

The Experiment

Remove your Silly Putty® from its package and form it into a nice round ball. Drop it onto a hard surface. What happens? It bounces back to you just like a rubber ball and demonstrates its elastic behavior.

Take that ball and stretch it. Does it bounce back to its original ball shape? No, it remains in its plastic deformed state and may even continue to slowly flow.

Roll the Silly Putty® back into a ball shape and flatten it. Securely grasp the putty in your two hands and quickly tear it apart by shearing. What happened? (Hopefully you tore it and not just stretched it — if not, move faster.) The Silly Putty® will fracture like a brittle material complete with fractured edges that look like broken glass.

Roll the Silly Putty® into a ball again and set it on the table top. What happens after several minutes? The Silly Putty® will flow like a very thick liquid. You just experienced four major mechanical behavior types of Silly Putty®!