Give you a meter ruler and a movie camera (which can take 24 photos per second). Please use these materials to design an experiment to study the ball rolling down the inclined plane.

If the steel ball moves in a straight line at a uniform speed, the displacement difference in continuous equal time is constant.

Experimental steps: let the steel ball roll down from the top of the inclined plane, at the same time, shoot the position of the small steel ball at different times with a movie camera, and measure the distance between two adjacent positions with a scale.

If the difference of displacement in consecutive equal time is equal, it is proved that the steel ball moves in a straight line at a uniform speed when rolling down the inclined plane.