impetus impetus /ˈɪmpətəs/

noun

1. () A force that moves something along  ( impulsion , drift , impetus )
   a force that moves something along
     The currents caused the drift of the floating debris towards the coastline.
   The currents caused the drift of the floating debris towards the coastline.
   
2. The act of applying force suddenly  ( impetus , impulsion , impulse )
   the act of applying force suddenly
    The impulse knocked him over
   the impulse knocked him over