Design and build a free-standing bridge that will support as much weight as possible. The bridge must span an opening of 30 cm and must be wide enoguh for a toy car to drive over it. (Materials can vary for this task: Spaghetti could be used again, or plastic straws, balsa wood, string, paddle pop sticks, masking tape, drawing pins, etc.)
Extra challenge and extra maths: The bridge must be as light as possible. The bridge with the best ‘strength to weight’ ratio wins.