Concept:A beam balance works on the law of moments, which says that an object is balanced when the total clockwise turning effect equals the total anticlockwise turning effect about the pivot.
Explanation:A beam balance has a horizontal beam supported at its midpoint by a sharp fulcrum.
The object being weighed is placed on one pan at a fixed distance from the fulcrum.
Standard masses are then added to the other pan until the beam becomes horizontal.
Each weight exerts a moment, which is the product of the force and its perpendicular distance from the fulcrum:
M=F×dFor the beam to rest in equilibrium, the clockwise moment on one side must equal the anticlockwise moment on the other side:
W1d1=W2d2Here,
W1 is the weight of the object,
W2 is the weight of the standard masses, and
d1 and
d2 are the equal distances of the pans from the fulcrum.
When both moments are equal, the beam becomes horizontal and the unknown weight is determined.
The principle of floatation deals with objects in fluids, conservation of energy concerns energy changes, and equivalence relates to mass and energy, so none of these govern the beam balance.
Answer:A. moments