The Lever Arm Balance

The lever arm balance compares the mass of an object to the mass of calibrated weights. There are two major types of lever arm balances. The equal arm balance [see Fig. 2.23(a)] works by directly comparing a known weight to an unknown weight, both of which are placed an equal distance from the fulcrum. Once in balance, there is a one-to-one ratio (of the weights) between the unknown and known weights. A well-made balance of this type is capable of high accuracy and preci- 

The unequal arm balance [see Fig. 2.23(b)] compares an unknown weight to the distance a known weight is to the fulcrum. When weighing an object, the further the balance weight is moved from the fulcrum, the heavier the object. The primary advantage of the unequal arm balance is that it needs only a limited number of calibrated weights. The disadvantage of this type of balance is that its accuracy is limited by how many divisions can accurately be defined between the units on the balance arm. 

Roberval principle used in equal and unequal style top-loading balance designs is shown in Fig. 2.25. 

The flexural pivot is free of the problems associated with the knife edge. However, it can act as a spring and therefore may add an extra force to the weighing process. This force may artificially subtract from an object s true mass and provide inaccurate readings. This effect may arise as a result of time or as temperature changes. Manufacturing design may decrease this effect, and it may also be 

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