do the action and the reaction forces within a third law pair act over the same span of time (delta t), or does one happen first then the other happens? the action happens and stops, then the reactions happens and stops. the action happens first, but the reaction then occurs while the action is still happening (they overlap). both stop simultaneously. the action and the reaction occur simultaneously: they start at exactly the same time, and they stop at exactly the same time. the action happens first, but the reaction then occurs while the action is still happening (they overlap) and continues to occur for a short period after the action has stopped.