activator animator appliance arouser bunt butt clout compulsion convenience drive driving force energizer engine enginery facility fixture human dynamo impellent impelling force impetus impulse impulsion incentive incitement irresistible force life locomotion machine machinery mechanical aid mechanical device mechanism mobility moment momentum motility motivating force motivity motor movableness power power plant power source propelling propelment propulsion pulsion push pushing restorative shove shoving shunt spark plug stimulant stimulator stimulus thrust tonic utility