Violin - The bow
The bow is an inwardly curved wooden rod with horsehair (approx. 150–250 hairs) stretched between the two ends, the point and the frog. The tension of the hairs can be adjusted with a screw on the frog. The center of gravity is about 25 cm above the frog. The bow is 74 cm long, the length of the bowstroke somewhat shorter.
Vibrations are produced by the bowing movement of the bow’s horsehair on the strings. This friction increases the temperature of the rosin applied to the horsehair, which ensures that the bow remains in contact with the string until the string’s elasticity causes it to spring back, whereupon the bow intercepts the motion and exerts new force on the string. The repeated back-and-forth movement of the bow provides the energy necessary for the vibration of the string.
The ideal bow pressure depends on the speed of bowing; too little pressure results in a weak fundamental note with whistling partials, too much causes rasping partials. Greater bow pressure naturally results in a louder volume. The point at which the bow makes contact with the string varies between the bridge and the fingerboard: the sound is loudest at the bridge and decreases in volume the further away from the bridge the bow moves.