Today they were introduced to the "Crash Box," a box filled with some sort of object in it, like a blown up balloon, a bunch of bolts, or some yarn scraps. One box is also just filled with air (although some students claim it's empty). Letting their cars go down their ramps, they made observations about what happened to the crash boxes.
Some crash boxes went farther than others. Kindergartners continue to ask "Why?!?!"