▁is ▁driven ▁by ▁tid al ▁forces . ▁A ▁moon ▁will ▁raise ▁a ▁tid al ▁bul ge ▁in ▁the ▁object ▁it ▁or bits ▁( the ▁primary ) ▁due ▁to ▁the ▁differential ▁gravit ational ▁force ▁across ▁diameter ▁of ▁the ▁primary . ▁If ▁a ▁moon ▁is ▁revol ving ▁in ▁the ▁same ▁direction ▁as ▁the ▁planet ' s ▁rotation ▁and ▁the ▁planet ▁is ▁rot ating ▁faster ▁than ▁the ▁orb ital ▁period ▁of ▁the ▁moon , ▁the ▁bul ge ▁will ▁constantly ▁be ▁pulled ▁ahead ▁of ▁the ▁moon . ▁In ▁this ▁situation , ▁angular ▁momentum ▁is ▁transferred ▁from ▁the ▁rotation ▁of ▁the ▁primary ▁to ▁the ▁revolution ▁of ▁the ▁satellite . ▁The ▁moon ▁g ains ▁energy ▁and ▁gradually ▁spir als ▁out ward , ▁while ▁the ▁primary ▁rot ates ▁more ▁slowly ▁over ▁time . ▁ ▁The ▁Earth ▁and ▁its ▁Moon ▁are ▁one ▁example ▁of ▁this ▁configuration . ▁Today , ▁the ▁Moon ▁is ▁tid ally ▁locked ▁to ▁the ▁Earth ; ▁one ▁of ▁its ▁revolution s ▁around ▁the ▁Earth ▁( current ly ▁about ▁ 2 9 ▁days ) ▁is ▁equal ▁to ▁one ▁of ▁its ▁rot ations ▁about ▁its ▁axis , ▁so ▁it ▁always ▁shows ▁one ▁face ▁to ▁the ▁Earth . ▁The ▁Moon ▁will ▁continue ▁to ▁re ced e ▁from ▁Earth , ▁and ▁Earth ' s ▁spin ▁will ▁continue ▁to ▁slow ▁gradually . ▁Other ▁examples ▁are ▁the ▁Gal ile an ▁mo ons ▁of ▁Jup iter ▁( as ▁well ▁as ▁many ▁of ▁Jup iter ' s ▁smaller ▁mo ons ) ▁and ▁most ▁of ▁the ▁larger ▁mo ons ▁of ▁Sat urn . ▁ ▁A ▁different ▁scenario