Make sure students realize how the behavior of their marbles reinforce the Law of Conservation of Energy: when marbles roll up a hill they lose kinetic energy and slow down, but at the same time they gain potential energy because they are gaining height.
(they; slow down; T:when marbles roll up a hill) (they; gain; potential energy; because they are gaining height; T:at the same time) (they; are gaining; height) (marbles; roll up; a hill)
they they they marbles
slow down gain are gaining roll up
T:when marbles roll up a hill
potential energy because they are gaining height T:at the same time
height
a hill