spring constant question... anyone?

[Anonymous Student]

why does the spring constant decrease as the temperature increase??

 

may i know the reason behind....?

[ShivaniVino]

I guess this is only applicable for metal springs, in which case the metal is probably less rigid due to increase in temperature. Perhaps the following explanation I found on answers.com would help: "A metal will melt if heated to a high enough temperature. Metal atoms are bonded together in a solid metal by forces that are derived from the difference in charge between a metal ion and an electron. In metals, rather than the particles that make them up being atoms, the atoms themselves split into positive ions and free negative electrons that are free to move between the metal ions. This is why metals are good conductors - the electrical charge can easily flow because of the free electrons that carry it. When a metal is heated, the ions that make up the metal vibrate more and more as the temperature increases. There comes a time when the amount of energy given to the metal is enough that the energy of vibration is more than that which holds the ions together, and so the ions too become free moving as the bonds between them break."

[Slovakov]

Just to clarify, this also applies to a lot of other materials. The mechanism is slightly different from one to the other (I'm not an expert on the molecular behaviour of materials so won't elaborate), but ductility of materials generally rises with temperature and increased ductility means decreased stiffness (in most cases).

On a simplistic level higher temperature means higher kinetic energy of particles so the bonds between molecules as well as within them are more strained, there are higher "gaps" between them. This means that under load the particles are more likely to re-arrange permanently, which on a large scale means tendency to more plastic behaviour. On the contrary, in low tmperature, particles are packed close together and under moderate load will remain whee they are, giving more elastic behaviour - the closer they are to each other, the stiffer the material.

 

In the extreme cases this can lead to materials becoming very brittle at low temperatures and extremely ductile at higher - the simplest example being plasticine - where in low temperatures the load is more likely  to break the bonds between the particles, while at high temperatures they vibrate so much that it takes quite a strain before it gets ripped.

Edited March 4, 2016 by Slovakov