Commentary Par XVIII 42

'It was joy that whipped that spinning top': That is, joy 'was the impulse which caused the rotation.  The homely simile is borrowed from Virgil (Aen. VII.378-384), where it is applied to Amata's wild excitement when under the influence of the Fury' (DDP Tozer.Par.XVIII.40-42).

In the days before mechanized toys, children used to keep their top spinning (once they had imparted energy to it by rapidly pulling a cord wrapped around it) by following it and 'whipping' its sides with a long, thin stick, thus maintaining its rotating motion.