Physics – dropping a slinky

Saw this video today on what happens when you first stretch out a slinky by letting one end hang free, and then let go for the other end. It’s pretty cool:

The explanation given in the video is that ‘the bottom of the slinky doesn’t know someone has let go of the top end’. This is no coincidence – longitudinal waves in a spring under tension will always have a lower speed of sound than a wavefront accelerating at that tension. Now to do the math…


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