Museo Galileo
Virtual Museum
Sensitivity of a balance

A balance is said to be sensitive when it can register small differences in weight. The balance beam is most sensitive when its center of gravity lies slightly below its rotation axis. If the center lies too far below the suspension point, the balance is too stable and therefore has low sensitivity (i.e., a considerable effort is needed to break the beam's equilibrium). If the center of gravity coincides with the rotation axis, the balance is in indifferent equilibrium: assuming equal weights, each position of the beam is stable. When the center of gravity lies above the rotation axis, even a slight difference in weight causes the beam to rebound abruptly.