Alex places 2 cubes side-by-side on a ramp made of wood. Cube #1 is ice and Cube #2 is wood
wrapped with sandpaper. The cubes are the same size and the same mass and are placed at the
same height on the ramp. When Alex released the two cubes, the ice cube slid down the ramp, but
the sandpaper cube did not move. What accounts for this difference?