Background
Although it looks like a form of clay, Silly Putty is actually a silicone polymer. It also has a few unique properties that make it very interesting scientifically — and fun! First, it is viscoelastic. That means it can be stretched and then pushed back together into its original shape, as if nothing had happened. Second, it is a non-Newtonian polymer, or a dilatant fluid. That’s a material that does not behave as it should — it does not follow Newton’s laws of viscosity. Finally, its apparent viscosity increases directly with respect to the amount of force applied. Without being too technical, it is a fluid that can be torn.
Ferrous compounds are materials that are naturally attracted by a magnetic field. Usually these materials include some form of iron, nickel or cobalt. Adding a ferrous material to Silly Putty will not drastically alter its original properties, but it will add some interesting new ones.
Why do this in your classroom?
- To encourage the following process skills for scientific investigation: prediction, observation, developing a hypothesis, and drawing conclusions
- To help students understand how magnetism works
- To show students how the make-up of a material affects its properties
Materials
- Silly Putty (24 g)
- Black iron oxide powder
- Neodymium magnet
- Disposable face mask
- Disposable gloves
Procedure
- Clear off your work area, and put on your face mask and gloves. Iron oxides come in a fine powder form and should not be inhaled.
- Play with the putty in your hands a little bit to loosen it up. Stretch it out a few times and roll it back into a ball. Repeat.
- Spread out the putty into a sheet and lay it on your work surface. Sprinkle the putty sheet with a layer of iron oxide.
- Fold over the putty and smooth it out again. Do this slowly to prevent the iron oxide from becoming airborne. Repeat this several times until the putty loses its color and turns black.
- Just as you did in step 2, play with the putty in your hands a little bit, stretch it out a few times and roll it back into a ball. Do this several more times.
- Now you have magnetic Silly Putty. Time to experiment and see how it reacts to your neodymium magnet.
- Caution: Since this is homemade, the magnetic putty has been known to leave a residue on some surfaces due to the iron oxide powder. Use caution when playing with your magnetic putty.
What’s happening?
The addition of iron oxide to the Silly Putty is going to change the properties and characteristics of the material. Now that it contains iron, the putty will be attracted to a magnetic field. Although the iron within it magnetizes weakly, it is also possible to make the putty repel as well. But magnetism isn’t the only thing that the addition of iron has done to the putty. Compare and contrast with some new, unmagnetized putty and see what other differences you can find.
For more information contact MagLab educator Carlos Villa.
