Three metal balls roll back and forth. When rolled one way all three balls roll side by side. When rolled the other way one ball rolls ahead of the other two. Students are challenged to explain why.
place the hollow sphere on the outside and up hill for the first roll reverse and roll the other way.
Four Ball Set (Ae4) Solid steel ball (66 g) Hollow steel ball(21g) Solid Aluminum ball (24g) channel (under stairs)