How does a balance measure weight?

A balance measures weight by comparing the gravitational pull on an object to a known standard, typically using a system of levers or weights. In this process, the object being weighed exerts a gravitational force that is balanced against the force of gravity acting on a known mass. When the forces are equal, the balance indicates that the weight of the object matches the weight of the known mass.

This method distinguishes itself from other approaches to measuring weight. For example, while a spring mechanism does measure weight in a different type of scale known as a spring scale, it relies on the deformation of a spring rather than directly comparing gravitational forces. Measuring the volume of an object is not a measure of weight; it relates to density when combined with mass. Furthermore, calculating pressure applied on the scale does not provide a direct measure of weight in terms of gravitational force; instead, pressure is related to the force distributed over an area, which is a different concept altogether.

Therefore, the correct choice highlights the fundamental principle of how a balance operates, based on the principle of equivalence between gravitational forces acting on the object and the reference weight.