The Physics of the Double Bass

    The double bass consists of four strings, each with a different thickness and tension. The tensions on the string are caused by the attachment of the strings to the four tuning pegs at the top of the instrument and the tailpiece at the bottom of the instrument. The tension of the strings can be adjusted (tuned) accordingly by turning the tuning peg. This will either loosen the tighten the string, and changing the tension in the string will change the note/sound that the string produces. A tighter string will produce a note with a higher frequency, which means that the number of soundwaves produced per unit of time will increase and produce a note of higher pitch. Thus, the tensions of the strings are very important in producing the different notes of the double bass, as different string tensions will create different notes.

    Friction is also essential in bowing, which is when you use a bow to produce sound by gliding it across the strings. In order for sound to be produced, the bow must vibrate the string. Therefore, I always put rosin onto my bow before I play. The rosin is made from tree sap, which is sticky and increases the friction between the string and the bow hair. Varying the pressure that you apply onto the string will change the volume of the sound that you produce as well. When you increase the pressure that you apply, the force of gravity acting on the bow and the string will increase. This means that the normal force on the string also increases, and the force of static friction will increase. As a result, the work that you must do to overcome the force of friction and drag the bow will increase. 

    A cool technique that you can perform on the double bass is spiccato, in which the bow bounces off of the string. The bow travels in an angular motion as it bounces from left to right. It is easiest to start doing spiccato at the fulcrum, which is the location of the bow’s center of mass. We can also think of it as the bow’s axis of rotation when we’re doing spiccato. Your hand is exerting a torque on the bow and causing it to bounce from side to side, rotating about the fulcrum. The reason why spiccato is done near the fulcrum is because it requires less effort from the musician. When you are bouncing the bow at the fulcrum (Point A), the amount of work that you are doing can be calculated using the following equation W=τΔθ= (rFsinθ)Δθ. However, if you bounce the bow closer to the tip at Point B (axis of rotation is now higher), the radius (rB) of the applied force is now farther from the axis of rotation. Therefore, the torque that you exert is now greater than if the fulcrum was the axis of rotation. This means that in order to rotate the bow through the same angle, you need to put in more work if your bow is the axis of rotation than if your fulcrum was the axis of rotation. Thus, if you want to make playing spiccato easier, you will want to play at the fulcrum and closer to the frog than at the tip of your bow.