my son got two of these for christmas, one from his dad and one from a friend. him and his dad went to hamleys and the assistants did a demonstration and said it worked by gravity and force and of course he thought it looked brill.but when he got it home he was very dissapointed when he found out that all you had was some string and some strong blu-tack. all you did was tie the string around your finger and swung it around. how boring. I would never recommend this to anyone!