In fact, the video states this for all convex shapes. I've been trying something similar for 2D, but there it doesn't quite seem to hold. Consider a very thin

In fact, the video states this for all convex shapes. I've been trying something similar for 2D, but there it doesn't quite seem to hold. Consider a very thin rectangle of size 1 by epsilon. Then it has circumference 2 (ignoring the epsilon). The shadow it casts at angle phi has size |sin phi|. Now, if we average |sin phi| from 0 to 180 degrees, (or 0 to 360 or 0 to 90) we get (2 / pi). I haven't checked whether this average holds for things other than thin rectangles, but I'd imagine so. I then find it weird we get a trancendental number in 2D but an integer in 3D.