The
spring scale apparatus is simply a spring fixed at one end with a hook to attach an object at the other. It works by
Hooke's LawIn mechanics, and physics, Hooke's law of elasticity is an approximation that states that the extension of a spring is in direct proportion with the load applied to it. Many materials obey this law as long as the load does not exceed the material's elastic limit. Materials for which 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.
The
spring scale apparatus is simply a spring fixed at one end with a hook to attach an object at the other. It works by
Hooke's LawIn mechanics, and physics, Hooke's law of elasticity is an approximation that states that the extension of a spring is in direct proportion with the load applied to it. Many materials obey this law as long as the load does not exceed the material's elastic limit. Materials for which 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.
Spring scales can be calibrated for the accurate measurement of mass in the location in which they are used, but 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. Also, the spring in the scale can permanently stretch with repeated use.
If two spring scales are hung one below the other in series, each of the scales will read the weight of the body hung on the lower scale. The scale on top would read slightly heavier due to being stretched by the weight of 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.
Uses
Spring scales can be used in physics and education as basic
accelerometerAn accelerometer is a device that measures proper acceleration, also called the four-acceleration. This is not necessarily the same as the coordinate acceleration , but is rather the type of acceleration associated with the phenomenon of weight experienced by a test mass that resides in the frame...
s, but its main uses are industrial, especially related to weighing heavy loads such as
truckA truck or lorry is a motor vehicle designed to transport cargo. Trucks vary greatly in size, power, and configuration, with the smallest being mechanically similar to an automobile...
s,
storage siloA silo is a structure for storing bulk materials. Silos are used in agriculture to store grain or fermented feed known as silage. Silos are more commonly used for bulk storage of grain, coal, cement, carbon black, woodchips, food products and sawdust. Three types of silos are in widespread use...
s, and material carried on a
conveyor beltA conveyor belt consists of two or more pulleys, with a continuous loop of material - the conveyor belt - that rotates about them. One or both of the pulleys are powered, moving the belt and the material on the belt forward. The powered pulley is called the drive pulley while the unpowered pulley...
. Spring scales are used when the accuracy afforded by other types of
scalesA weighing scale is a measuring instrument for determining the weight or mass of an object. A spring scale measures weight by the distance a spring deflects under its load...
can be sacrificed for simplicity, cheapness, and robustness.
A spring balance measures the weight of an object by opposing the force of gravity with the force of an extended spring.
History
The first spring balance in Britain was made around 1770 by Richard Salter of
BilstonBilston is a town in the English county of West Midlands, situated in the southeastern corner of the City of Wolverhampton. Three wards of Wolverhampton City Council cover the town: Bilston East and Bilston North, which almost entirely comprise parts of the historic Borough of Bilston, and...
, near
West BromwichWest Bromwich is a town within the Metropolitan Borough of Sandwell, in the West Midlands, England. It is north west of Birmingham lying on the A41 London-to-Birkenhead road. West Bromwich is part of the Black Country...
. He and his nephews John & George founded the firm of
George Salter & Co., still notable makers of scales and balances, who in 1838 patented the spring balance. They also applied the same spring balance principle to steam locomotive
safety valveA safety valve is a valve mechanism for the automatic release of a substance from a boiler, pressure vessel, or other system when the pressure or temperature exceeds preset limits....
s, replacing the earlier deadweight valves.
See also
- Weighing scale
A weighing scale is a measuring instrument for determining the weight or mass of an object. A spring scale measures weight by the distance a spring deflects under its load...