Exhibit: Roll Uphill
Put the cone-shaped roller on the track at the lower end and let go. The roller rolls up the track towards the upper end, apparently defying gravity. Although the roller moves to the upper part of the track, the roller actually gets lower while it is rolling. This is because the track gets wider apart towards the upper end. The roller begins on the track and because of its shape, wide in the middle, it rolls upwards. As the track rises, it gets wider, so the roller rolls on a narrower part of the cones. This more than offsets the rise of the track so the roller itself gets lower and carries on rolling. The track has to be designed so that the cones fall more than the track rises.