An apparatus or educational toy comprising a main body (120, 220, 320, 520) and a drive mechanism (140, 240, 340, 540), wherein the drive mechanism (140, 240, 340, 540) comprises a reservoir (142, 242, 342) for storing a driving liquid, a discharge outlet (144, 244a, 244b, 344, 544a, 544b) through which the driving liquid is discharged from the main body (120, 220, 320, 520) to generate a driving thrust, a liquid delivery path (146, 246a, 246b, 346) for delivering the driving liquid for a reservoir outlet (148, 348, 448) to the discharge outlet (144, 244a, 244b, 344, 544a, 544b), and a threshold setting device (147, 347); and wherein the threshold setting device (147, 347) sets a threshold thrust level so that the driving liquid is to pass from the reservoir (142, 242, 342) and discharged from the discharge outlet (144, 244a, 244b, 344, 544a, 544b) upon reaching the threshold thrust level during operation.
