Smartivity Stop Drop Gravity Transporter consists of a pulley-mechanism, a cart and track section with dispensing holes and collectors for marbles. As children place or remove marbles, the speed with which the cart moves along the track changes. Children are challenged to deposit marbles in a particular collector. This task can be accomplished only at a particular speed of the cart. Children have to analyse and decide what particular weight will result in the right speed of the trolley’s movement.