This video shows how a slinky, which is being held at the top with its bottom freely dangling, falls when released.

Students are asked to predict what happens when the slinky is released.  Does the top fall first? Does the bottom fall first? Do both ends fall together or does the centre of the slinky remain at rest with top and bottom ends moving towards each other?

A slow motion video shows that the bottom end stays stationary while the top moves towards it.  As they meet the collapsed slinky then moves towards the ground. This happens because the bottom end has balanced forces acting upon it (gravity pulling it down and tension in the spring pulling it up). Only when the top meets the bottom does the change in force make the whole slinky move downwards. This delay is due to the relatively slow speed of the compression wave propagating through the spring.

Slinky drop - answer

This video explains why the slinky falls in the way it does.

Slinky drop - extension

This video demonstrates the slinky drop experiment with a tennis ball attached to the bottom of the slinky.  It explains why the same motion is seen in terms of the balanced forces experienced by the bottom of the slinky.

Only when the top of the slinky reached the bottom does the whole slinky begin to fall.  This is because it’s at this point that the information about changes in force reach the bottom.

Slinky drop - slow motion

This video shows how a stretched slinky moves when its top is released.  The explanation given in previous videos is extended to show that the same motion is seen if the extended slinky is hit by a horizontal force to collapse it.

How does a slinky fall?

This video shows a slinky being dropped with a tennis ball attached to its bottom. The same motion is observed because the bottom has balanced forces.  It’s at the top where forces have changed.

Awesome HD slinky drop - slow motion

 This video shows a slinky being released from its top in slow motion.  The motion is also modelled using a computer.