The ball that is “forced” around in a circle must be forced round in that circle by an external force, in this case, the walls of the looped plastic tube, applying a force vector that points towards the centre of that loop of tube. That force causes friction, which slows the ball down, so the ball traveling in straight line (that just has friction from it’s mass only (Acting downwards) is decelerated less, so travels further in the same time period.Ok, so the friction increases so much to slow it down by 20+%. Really? A metal sphere is not gonna deform to increase its contact patch.