Spring Constant of Springs in Series and Parallel Planning The aim of this investigation is to examine the effect on the spring constant placing 2 identical springs in parallel and series combination has and how the resultant spring constants of the parallel and series spring sets compare to that of a lone spring with identical spring constant. Hypothesis -???- Hooke?s Law states that "The magnitude of the spring constant (k) is equal to the stretching force applied (F) divided by the resultant extension (x)", it should be possible to determine a spring constant for each spring set. Due to existing knowledge of springs I propose that the series spring set will have a lower spring constant (and hence due to Hooke?s Law display a greater extension) than the parallel spring set. Also, as Hooke?s Law is a linear function, the spring constant of the series spring set should be exactly half that of a single spring, whereas the spring constant of the parallel set should be exactly double that of the single spring. This also means that if the resulting extension or spring length of the spring sets are graphed along a y axis with the increasing force mapped to the x axis (so that the results can be displayed in a traditional scientific graph fashion), the gradient will be the inverse of the spring constant. This hypothesis is backed up by many sources, one such source is ?Physics? by Ken Dobson, David Grace and David Lovettwhich in the 2000 edition states on page 90 that the spring constant of 2 springs in series is k = k/2 and for 2 springs in parallel k = 2k This hypothesis will probably only hold true however while the spring extends at a directly proportional rate to the increase in force on the spring
This is because every material has an elastic limit which is the percentage of extension a piece of material can be stretched to and still return to its original form. As the magnitude of extension of the string approaches this elastic limit, the extension will gradually cease to obey Hooke?s law. At this elastic limit, several changes in the composition of the spring can be observed. Whereas any stretching of a material that occurs below up until this limit is referred to as elastic deformation, stretching the material beyond this limit will result in permanent deformation of the material. Stretching that occurs beyond the elastic limit is referred to as plastic deformation. Once a spring has been stretched beyond its elastic limit, its molecular composition is permanently altered, meaning that the molecules that comprise the material have permanently re-arranged themselves as a result of energy transferred during the stretching process. Removing the force that is causing the stretch will not result in the material returning to its original state. Instead it will return to a semi-stretched state. When being stretched, the properties that a material displays falls into 1 of 3 categories, it will be either:
Ductile
The material has a period of uniform elastic stretching, then a
period of non-uniform plastic stretching until breaking point is
reached. Examples: Iron, Copper
Brittle
The material displays uniform elastic stretching until it reaches
its elastic limit at which it breaks. Examples: Stone, Glass
Polymetric
The material has a short period of uniform elastic stretching, it
then has a long period of parabolic plastic stretching until
breaking point. Examples: Rubber, Petroleum based materials