Summary Originally designed on Orchard (https://3DOrchard.com), this Mechanical paradox is inspired by the up-hill roller: (https://plus.maths.org/content/defying-gravity-uphill-roller). This device could help in classrooms, illustrating concepts of gravity, center of mass, momentum, and friction, to name a few. This hasn't been tested. The incline may need to be reduced or the angles modified. Luckily, the model is easy to edit/print at its original location: (https://3dorchard.com/#!/single/582d7ad1b57c4f800a2b4368/584da5179092ef990b346d54) How I Designed This Sketching the cut profile for the notch in the Orchard modeling interface (https://3dorchard.com/#!/single/582d7ad1b57c4f800a2b4368/584da5179092ef990b346d54) Pulled (extruded) the 2D sketch into a 3D object to create a block, cut the block. ( Model can be found at: https://3dorchard.com/#!/single/582d7ad1b57c4f800a2b4368/584da5179092ef990b346d54) Designed in the Orchard modeling interface: https://3dorchard.com/#!/single/582d7ad1b57c4f800a2b4368/584da5179092ef990b346d54