The number one call we get from parents of beginning string students is, “the bow is broken, we pull it across the string and there is no sound.”  Some of you have already guessed at the problem – no rosin.  Rosin is an essential component of the vibration chain that produces sound from the instrument.  The stick of the bow holds the bow hair taut, the rosin on the hair creates the friction that causes the string to vibrate, the string vibrations travel through the bridge to the top of the instrument and the instrument amplifies those vibrations into the sound we hear.  Without the rosin, the chain is broken.