Yesterday at my violin lesson, my violin teacher spent the entire hour working with me on cleaning up my sound quality (I am playing a Mozart Concerto, so the sound has to be crisp and clean). The main thing my teacher suggested in order to get rid of the crunchy and unclear sound I was producing was to apply a greater force to the bow. After only a few tries, my sound became significantly clearer. I figured there had to be some physics behind why a larger force resulted in a clearer tone. Us violinists put rosin, a white colored powder, on our bows in order to increase the friction and therefore the force between the bow and the strings (friction, of course, exists already between the bow and the violin when there is no rosin, but rosin increases the friction, which stops the bow from sliding and consequently, the violinist from losing control. If there were no friction between the bow and the strings, then the strings would not vibrate and there would be no music created. The violinist then applies a force (depending on the direction in which they are bowing), so that they can overcome the force of friction and get the bow to move with a certain velocity (work = change in kinetic energy application). Music is created because the friction between the bow and the string causes the bow to "catch" the string; in other words, the bow grips the string, then releases it, then grips it then releases, etc. This motion occurs over and over as the bow moves up and down, resulting in oscillations of the string which translate into sound. If a violinist does not apply enough force, then they cannot overcome the static friction between the bow and the string. So, the string does not vibrate; the scratchy sound is produced from the lack of vibration and from the work which the smaller force is doing on the string (conservation of energy application). By applying a larger force, the violinist fully overcomes the static friction, which allows the bow to catch the string and then for the string to release and to continue this oscillation, which results in a much purer and enjoyable sound.