The Storm-Cleared Soccer Field Test

The Storm-Cleared Soccer Field Test

1A strong storm left puddles around the soccer field, so the grounds crew waited until the rain stopped. The crew wanted to decide where to place small catch trays while checking a raised equipment platform for loose objects. They tested the direction of motion without adding a push. For each trial, a student held a rubber practice ball at a marked height and released it. The crew kept the ball, release height, and number of trials the same. They changed the platform location. A second student watched the ball's first motion before it landed.

2At the north platform, all 8 of 8 balls first moved toward the turf. At the east platform, all 8 of 8 balls first moved toward the turf. At the west platform, all 8 of 8 balls first moved toward the turf. The crew then gave six balls a gentle forward push at the east platform. All six moved forward while also moving toward the turf. The forward push changed part of the path, but the balls still moved toward the turf.

3The crew made a small spherical Earth model from a foam ball. Its center was marked O. On the model, the soccer field was near the surface. The crew marked P at the top of the model, Q at the right side, and R at the bottom. An arrow that represents a pull toward Earth's center must point from each mark toward O. Thus, the arrows point in different page directions at P, Q, and R even though each arrow points toward the same center.