What feature of balance scales allows them to determine weight?

Balance scales determine weight by achieving equilibrium between two sides. This is based on the principle of balancing forces, where the weight of an object placed on one side is compared to a known weight on the other side. When the scale is in equilibrium, it indicates that both sides exert an equal downward force due to gravity, allowing for a direct measure of the object's weight.

As for the other options, they do not accurately describe the fundamental operation of balance scales. The mechanism for measuring electrical resistance is unrelated to weighing objects. The height of the scale's arms does not influence how weight is measured; instead, it's the balance achieved that is crucial. Lastly, while the material may affect the durability or precision of the scale, it does not play a direct role in the actual measurement process. Thus, the equilibrium achieved between the two sides is the feature that allows balance scales to accurately determine weight.