Objects in motion attract children. The following activity helps children explore the motion of bodies riding in a vehicle and safely demonstrates the answer to their questions, "Why do I need a seatbelt?" Children will enjoy moving the cup around, even if all they "see" is a cup rather than understanding it represents a car. They will understand that each time they suddenly stop the cup, the marble will roll out unless it is taped in, even if they do not yet understand that the same forces apply to passengers in a car.