3. Active, energetic, strenuous, vigorous imply a liveliness and briskness in accomplishing something. Active suggests quickness and diligence as opposed to laziness or dilatory methods: an active and useful person. Energetic suggests forceful and intense, sometimes nervous, activity: conducting an energetic campaign. Strenuous implies arduous and zealous activity with a sense of urgency: a strenuous effort. Vigorous suggests strong, effective activity: using vigorous measures to accomplish an end.

Did you mean active mass?