The word ‘isochronal‘ means “equal or uniform in time”—iso meaning equal and chrono referring to time—which all makes sense when watching the mysterious isochronous curve video above.

In this old Curiosity Show clip, science educator and co-host Rob Morrison demonstrates how to draw an isochronous curve and why these curves are extraordinary. Watch as every steel ball dropped on any point in the curve meets in the middle of the curve at the same time as a marble dropped from any point on the other side.

The award-winning Curiosity Show ran from 1972 to 1990 for school-age kids in Australia. Co-hosts Morrison and Deane Hutton won the rights to the show in 2012, and now share clips on their YouTube Channel.

Next watch more geometry videos, and more from The Curiosity Show: How to make a self-starting siphon, the Matchstick Triangle Puzzle, and how does a music box work?