What Is It?
A spring scale determines weight by measuring the amount of weight deflected when an object (or person) is placed on the spring scale. The make-up of a typical spring scale includes a stand, measurement tool, spring and an object for measurement, and contemporary examples of a spring scale include a scale that measures the weight of produce at a grocery store or a bathroom scale.
The spring scale operates on Hooke's Law of Physics: A spring will extend in proportion with the load added to it, providing this load does not exceed the limits of elasticity.
Force is Exerted
The position of the spring is measured before the person steps onto the spring platform. Once the person to be measured is on the spring scale, she exerts force, causing the spring scale to stretch and drop lower because it is pulled by gravity. Then, the ending position of the spring is recorded, either on a digital or analog readout. The amount the spring moves is typically associated with a certain amount of weight. While measuring, it is important to keep in mind the rule regarding elastic limit: A spring can stretch so far that it exceeds its elastic capabilities and can therefore break.
Formula for Measurement
The formula used to calculate weight is weight equals mass multiplied by grams (gravity is typically signified by 9.8 m/(S x S). This measurement typically is calculated as either newtons or pounds-force. Bathroom scales have already performed the calculations necessary to measure weight and may include a ruler-type measurement that shows an person's weight when he stepped on a scale. However, others may use a homemade scale to calculate the starting and ending positions to determine the level of force used to measure on a spring scale. For this, force equals the stretch multiplied by the constant of proportionality. In this instance, proportionality typically is a straight line---as in, the more weight applied, the higher the amount of force.
The spring's length and stretch often depends upon the maximum weight to be measured although the general rule is: the longer the spring, the more weight that can be measured. It is important to ensure a spring scale always stays properly calibrated to ensure a spring scale rests at 0 pounds.
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