▁the ▁por os ity ▁and ▁flat ness ▁of ▁the ▁surface ▁and ▁the ▁properties ▁of ▁the ▁cup ' s ▁rim . ▁A ▁small ▁amount ▁of ▁min eral ▁oil ▁or ▁veget able ▁oil ▁is ▁often ▁employed ▁to ▁help ▁maintain ▁the ▁se al . ▁ ▁Calcul ations ▁ ▁The ▁force ▁required ▁to ▁det ach ▁an ▁ideal ▁su ction ▁cup ▁by ▁pulling ▁it ▁directly ▁away ▁from ▁the ▁surface ▁is ▁given ▁by ▁the ▁formula : ▁ ▁where : ▁F ▁is ▁the ▁force , ▁A ▁is ▁the ▁area ▁of ▁the ▁surface ▁covered ▁by ▁the ▁cup , ▁P ▁is ▁the ▁pressure ▁outside ▁the ▁cup ▁( typ ically ▁atmos pher ic ▁pressure ) ▁ ▁This ▁is ▁derived ▁from ▁the ▁definition ▁of ▁pressure , ▁which ▁is : ▁ ▁For ▁example , ▁a ▁su ction ▁cup ▁of ▁radius ▁ 2 . 0   cm ▁has ▁an ▁area ▁of ▁( 0 . 0 2 0 ▁m ) 2 ▁= ▁ 0 . 0 0 1 3 ▁square ▁meters . ▁Using ▁the ▁force ▁formula ▁( F ▁= ▁AP ), ▁the ▁result ▁is ▁F ▁= ▁( 0 . 0 0 1 3 ▁m 2 )( 1 0 0 , 0 0 0 ▁Pa ) ▁= ▁about ▁ 1 3 0 ▁new tons . ▁ ▁The ▁above ▁formula ▁re lies ▁on ▁several ▁assumptions : ▁ ▁The ▁outer ▁diameter ▁of ▁the ▁cup ▁does ▁not ▁change ▁when ▁the ▁cup ▁is ▁pulled . ▁ ▁No ▁air ▁le aks ▁into ▁the ▁gap ▁between ▁the ▁cup ▁and ▁the ▁surface . ▁ ▁The ▁pulling ▁force ▁is ▁applied ▁per pend icular ▁to ▁the ▁surface