I was going through the Hooke's law and studying about Springs in general. One question which is bugging me is whether "Force by a spring" essentially yet another force of tension (just like in a rope).

I read the following, on the following link, https://www.khanacademy.org/science/physics/work-and-energy/hookes-law/a/what-is-hookes-law

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So a bunch questions on which I am seeking clarity,

  1. The coil shape has nothing to do with the "spring" or "spring force"?

  2. Is spring as good as a rope when considering how it acts when subjected to force? Or is "Elastic force" different than "force of tension".

Also, am I thinking correctly here? The difference is, ropes can only be pulled and NOT pushed (upon push rope will slack), but springs can be pulled and pushed upon. But fundamentally the force at microscopic level is same in either rope / spring.


Yes, the forces involved are interatomic (and so fundamentally electromagnetic) in the case of a stretched spring, as for a stretched wire or a stretched rope.

I think, though, that the passage you quote is misleading. If you formed a helical spring out of a metre of steel wire, then the extension of the spring when subjected to equal and opposite forces at either end would be much greater than the extension of the original wire when subjected to the same pair of forces. This is because, for the spring, there is twisting and bending of the wire. Extension of the wire along its length is negligible by comparison. The shape of the spring is indeed magical!

  • $\begingroup$ So the "coil" shape is necessary in spring? Can a metallic chord be called a spring? $\endgroup$ – Sushant Gupta Jul 10 '17 at 18:01
  • $\begingroup$ Do you mean by 'chord' a piece of rod or wire under tension? If so, I don't think it would usually be called a spring. But 'leaf springs' in vehicles $are$ just bars of metal, but the elastic deformation is bending rather than straightforward stretching along their length, so I don't think they're what you're interested in. $\endgroup$ – Philip Wood Jul 10 '17 at 18:10
  • $\begingroup$ I don't think there is any significant change directly to the length of a wire in a spring by the way. A helical coil spring is just a long bar being twisted; wound in a helix so that twisting acts in the horizontal plane while the coils are allowed to move vertically relative to each other. $\endgroup$ – JMac Jul 10 '17 at 20:00
  • $\begingroup$ You're absolutely right. But bending of the wire is also significant. There's a neat analysis in that ancient textbook $Properties of Matter$ by Champion and Davy. $\endgroup$ – Philip Wood Jul 10 '17 at 20:04
  • $\begingroup$ @PhilipWood Is there technically any non-torsional bending involved? Due to the nature of the shape, the act of bending the coils flat against each other can really be seen as twisting the bar. If you imagined the stresses on the coil straightened out it shouldn't be bent, just twisted (for an ideal spring). I guess it depends how you want to analyze the coil; but as a straight wire the analysis should be pure torsion AFAIK. $\endgroup$ – JMac Jul 10 '17 at 20:14

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