Hold slinky by a few turns at its top
so it stretches vertically under its own weight. Release slinky so
it falls freely. Bottom remains stationary until slinky has fully collapsed.
Motion demonstrates equivalence of weightlessness and free fall.
NOTES
One can use the long (wave-demonstrator)
slinky held out the second floor window with observers below.
REFERENCE
Ronald Newburgh and George M.
Andes, "Galileo Redux, or How Do Nonrigid, Extended Bodies Fall?" TPT
33, 586-588 (1995).