Balance Scales

Balance scales consist of a two-armed lever (the balance beam) with arms of equal length. At the ends of these arms are weighing pans, where the object to be measured is placed on one side, and reference masses are placed on the other. In the center of the balance beam is a vertical pointer, which helps indicate when the two sides are in balance. For accuracy and sensitivity, the fulcrum of the balance beam must be nearly frictionless, typically achieved by using a knife-edge design. An arrestment knob allows the beam to lift from the knife edge and immobilize the scales when not in use. While balance scales are simple in design, a well-engineered suspension system makes them highly sensitive. However, balance scales have certain disadvantages, such as their sensitivity to external shocks and the requirement of a set of reference masses. The scales are in equilibrium when the torques on both sides are equal. If the force on one side is greater than the other, the beam will tip, indicating that the scales are out of balance.