pojačati

1. (of sound, a device) to turn up
   Pojačaj malo radio, ne čujem vesti. — Turn the radio up a bit, I can't hear the news.
   Pojačala sam grejanje jer je hladno. — I turned up the heating because it's cold.
2. to strengthen; to reinforce
   Policija je pojačala kontrole na granici. — The police stepped up checks at the border.
   Klub je pojačao tim sa dva nova igrača. — The club strengthened the team with two new players.
3. (pojačati se) to intensify; to get stronger
   Uveče se vetar pojačao. — In the evening the wind picked up.
   Bol se pojačao posle ručka. — The pain got worse after lunch.

The imperfective is pojačavati.