Singing Road! If you drift off the side of a road and hit a rumble strip, you’ll get a distinctive sound intended to alert you and prevent an accident. The pitch of the sound you get depends on the spacing between the bumps or ridges. So if you make lots of ridges like a rumble strip and vary the spacing between the ridges correctly, then different musical notes can be made. Close together ridges (say 6mm apart) give high notes, and far apart ridges (say 12mm apart) give low notes. Make the right pattern of ridges then as a car drives over them, a tune is played. Here’s a story of how Honda tried this for an advert then totally fudged it up.