Falling slinky

When a slinky is suspended in mid air until it reaches equilibrium and then dropped, it falls in a very peculiar manner.

The bottom of the slinky would appear to hover in mid-air until the turns start stacking up from the top and eventually reach the bottom.

A slow motion video has been made by scientists to help us analyze the motion of the slinky quite nicely.

Mike Wheatland from Australia’s University of Sydney explains :

When you let go of the slinky at the top, “there’s a finite time for that information (i.e. signal) about that change to get to the bottom of the slinky.”

At t=0 (When the slinky is released),

Force at top = mg + T

Force at bottom = mg - T (These forces cancel each other, hence the hovering effect)

Force at center of mass = mg + T - T = mg (Falls freely)

W.G. Unruh, a physics professor at the University of British Columbia, has written a paper in which he mathematically tackles the problem of the falling slinky.

Further reading