Spring scale

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Spring scale.

A spring scale (or spring balance) is a weighing scale often used to measure force, such as the force of gravity, exerted on a mass or the force of a person's grip or the force exerted by a towing vehicle. This force is commonly measured in newtons, for which one newton corresponds to about a tenth of a kilogram of mass, or about the weight of an apple. The spring scale can also be correctly called a Newton Metre, because it is used to measure newtons.

The spring scale apparatus is simply a spring fixed at one end with a hook to an attach an object at the other. It works by Hooke's Law, which states that the force needed to extend a spring is proportional to the distance that spring is extended from its rest position. Therefore the scale markings on the spring scale are equally spaced.

Many spring scales are marked right on their face "Not Legal for Trade" or words of similar import, due to the approximate nature of the theory used to mark the scale. The spring in the scale can permanently stretch with repeated use, so most spring scales can be calibrated for the accurate measurement of mass in the location in which they are used.

If the two spring scales are hung one below the other both will read the weight of the body hung on the lower scale.

Spring scales come in different sizes. Generally, small scales that measure newtons will have a less firm spring (one with a smaller spring constant) than larger ones that measure tens, hundreds or thousands of newtons.

Spring scales can be used in physics and education as a basic accelerometer, but its main uses are industrial, especially related to weighing heavy loads such as trucks, storage silos, and material carried on a conveyor belt. Spring scales are used when the high accuracy afforded by other types of scales can be sacrificed for simplicity, cheapness, and robustness.