Spark image
Stretching a rubber band

Rubber is a polymer that means that the rubber molecules are made of long chains of atoms.

When a rubber band is unstretched the molecule chains are all twisted up. As the rubber is stretched they begin to untangle themselves. When they are all lined up the the surface looks rougher and whiter.
At the start it was quite easy to stretch the rubber band but now it becomes much more difficult to stretch. This is because up to this point the long chain molecules have been untangling but when the molecules are straight they cannot be untangled any more and it is the molecules themselves that are stretched!

© Keith Gibbs 2008