pinners! - how do fidget spinners work? - Quick Physics Video

Fidget spinners work because there is a bearing in the centre. This is a good example of conservation of angular momentum, essentially the thing will keep spinning until there is an external moment, this is provided by the friction between the two rings. Ball bearings in between the two rings mean that as small as possible surface is touching between the two rotating rings, meaning friction is as low as possible. Skateboards, rollerblades, bikes and cars are all designed to waste as little as possible energy as heat and sound during friction between the axle and the wheel.