What scientific principle do 2nd graders learn when rolling a ball down a ramp at different angles?

When 2nd graders roll a ball down a ramp at different angles, they are primarily exploring the relationship between gravity and an object's motion. The ramp's angle affects how much gravitational force acts on the ball as it rolls down, which in turn affects the speed and distance the ball travels. As the angle increases, gravity exerts a stronger pull, resulting in a faster acceleration of the ball. This practical experience allows students to observe and understand how gravity influences the motion of objects, which is foundational in their comprehension of basic physics concepts related to motion.

The other choices address important concepts as well, but they do not specifically encapsulate the primary focus of this type of experiment. For instance, while speed and distance are related, the main factor driven in this case is gravity's effect on the ball's motion rather than just measuring speed based on distance. Concepts like conservation of energy and friction are also important in broader contexts, but they are not the central scientific principle students are specifically investigating when manipulating the ramp’s angle in this hands-on activity.