Ask A Scientist© Biology Archive

Question:  I could use information on why silly putty bounces and why Jello 
jiggles in relation to polymers.  Thanks.
Robert A Kinson

Answer:  Silly putty is made of long flexible molecules all tangled up. If you
just let the putty sit or smoosh it with your fingers, the molecules slide
over each other and the material flows. When you drop it, the impact tries
to make the molecules move past  each other very fast.  They can't do this,
they're too tangled, so instead the molecules deform, like stretched and
compressed slinkies. Then after the ball stops, they rebound to where they
were, and this generates the force that causes the ball to bounce up.
Jello is also made of long flexible molecules tangled up (with a lot of
water in between), but in this case they're also attached to one another,
so they can't move past each other at all.  So Jello won't flow no matter
how slowly you moosh it.  All that happens eventually is that the molecules
or the junctions break, or more complicatedly, the network slips along a
fault, and the Jello rips or crumbles.
Christopher Grayce