Since the student is trying to determine the amount of time needed for the ball to roll down the incline, based on the angle of incline.
The independent variable: the amount or extent of the angle, the angle of inclination of the ramp, as this somewhat dictates the amount of time needed for the ball to roll down the ramp.
The dependent variable: the barnacle you are measuring, in this case, the time for the ball to roll down the ramp at different inclination angles.