Straight Rod Passing Through Curved Hole

This was at the Science Museum in Valencia, Spain. Although it looks impossible, this solid metal bar can pass through a curved slot. It works because the rod is angled and rotated through space by a three-dimensional shape with a hyperbolic cross-section. Therefore if the slot is the exact shape of this hyperbola, the rigid straight rod can pass through it. 

It’s a really good thing to look at if you want to know how time/space is curved. What the hole in the plastic represents is not the shape of the pole but a cross-section of the pole plotted against time. Really nice geometry.

Ali Kaya


Ali Kaya

This is Ali. Bespectacled and mustachioed father, math blogger, and soccer player. I also do consult for global math and science startups.

Similar Videos


An audiovisual piece made up of over four thousand still images pulled from Google Earth, individually edited, and then manually sequenced to Midnight by Caravan Palace.
Binary Counter | Video | Abakcus

Binary Counter

Are you looking for a stunning math project idea to showcase binary numbers? Then, here is a beautiful mechanical binary counter for you! With its intricate design, this counter provides…