A physical balance works on the principle of compensation. It has two pans, in one pan the substance whose weight has to be found is placed and in the other, different weights are added until it is equal to the weight of the substance. it is indicated by the movement of the pointer. In the case of the spring, the substance is attached to the spring and the expansion of the spring which is calibrated is noted down which depends on the weight of the substance.
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Two main differences: Physical balance works on the principle of balancing known mass with unknown, while spring balance notes the mass proportional to the extension of the spring; in spring balance only one pan (or Hook for placing the item while physical balance has two, for balancing.