A shape memory alloy
is a type of metal
which has the property
of being able to contract
a certain length
when heated to a certain temperature
then revert back to the start length after cool
ing past a certain temperature. A commercial name for such a product is Muscle Wire
. Shape memory alloys are generally available in wire
form and a small current
is usually enough to heat
them past the temperature at which they contract.
I won a copy of the Muscle Wires Project Book (complete with samples of Muscle Wire) through a drawing at Robot Wars (AFAIK the only one that ever took place in SF). It 'got lost' in my ex's house though so I never got to play with it.