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
cooling 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.