A model of vibrating atoms in a solid This model shows atoms
making up a crystal held together by spring-like forces.
Apparatus and materials Health & Safety and Technical notes The
model recommended is large and wobbly. The more rigid types
often used in chemistry departments are not suitable. Apparatus
manufacturers may stock the version needed. The most useful
versions are those where the springs are weak enough for the
model to wobble like a jelly. However, it must be able to stand
up on its own. Alternately, a model may be made from foamed
polystyrene spheres (or even the more massive golf balls) and
weak steel springs. The springs have loops on each end and are
intended for stretching experiments. Each one should be pre-
stretched a little so the coils are separated. Slots are made in
the spheres (a very hot domestic table knife blade works well)
and the loops on the springs glued into slots. A cubical array
of 27 spheres will do. The model is used as a 'prop' to support
a discussion of the way in which