What Factors Affect the Value of Spring Constant?

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Discussion Overview

The discussion centers on the factors affecting the value of the spring constant, particularly in the context of helical springs. Participants explore the mathematical relationships and physical principles involved in determining the spring constant, including the effects of wire twisting and bending.

Discussion Character

  • Technical explanation
  • Exploratory
  • Conceptual clarification

Main Points Raised

  • One participant suggests that the spring constant for a helical spring can be approximated by the formula k = \frac{\pi r^4 n}{2 a^2 L}, where r is the radius of the wire, n is the rigidity modulus, a is the radius of a turn, and L is the length of the wire.
  • Another participant questions whether the springiness of a helical spring is solely due to the potential energy stored from twisting the wire or if there are additional factors involved.
  • A participant introduces the concept of extension due to bending of the wire, noting that this is inversely proportional to Young's modulus and typically smaller than the extension due to twisting.
  • Several participants reference historical texts on the properties of matter that may provide further insights into the behavior of springs.

Areas of Agreement / Disagreement

Participants express varying views on the factors influencing the spring constant, with some focusing on twisting and others on bending. There is no consensus on whether additional factors beyond twisting contribute significantly to the spring constant.

Contextual Notes

Participants mention limitations in finding derivations and references for the discussed formulas, indicating a potential gap in accessible resources on the topic.

Who May Find This Useful

This discussion may be of interest to students and professionals in physics and engineering, particularly those studying material properties and mechanical systems involving springs.

A Dhingra
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hello everyone!

can you please explain on factors the value of spring constant depends?
And please provide me with the required maths to get to that idea..

Thanks..
 
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I assume you have in mind a helical spring. The main process involved in stretching such a spring is twisting the wire of which it is made. The torque needed to twist the wire through a given angle is proportional to r4 in which r is the radius of the wire, and is also proportional to the rigidity modulus, n, of the wire. Provided the turns of the spring remain almost at right angles to the longitudinal axis of the spring, then the spring constant is given approximately by
[tex]k = \frac{\pi r^4 n}{2 a^2 L}[/tex]
in which [itex]a[/itex] is the radius of a turn of the spring and [itex]L[/itex] is the length of the wire from which the spring is made.
 
Hence the springiness of a helical spring is only due to the energy stored as potential due to the application of torque to twist the wire. Is it correct? or there is something more to it?

Thanks a lot..
 
There is also extension due to the bending of the wire (as the wire is effectively a compacted cantilever). This bending is inversely proportional to the Young's modulus. The geometry of the spring is usually such that this component of extension is smaller than that due to the wire twisting.

Champion & Davy treat springs in their 'Properties of Matter' (no doubt long out of print - it was beginning to look old fashioned in the late 1960s!) No doubt mechanical engineering textbooks would be a good bet.
 
Thanks a lot.
one more request, i tried looking up for a derivation of this formula on Google but could not find it. Can u suggest me a required link for the same or some book to refer this from.
 
I know of two 'Properties of matter' books that deal with springs.
'Properties of Matter' by Champion & Davy published by Blackie in the UK.
'The General Properties of Matter' by Newman & Searle published by Arnold in the UK.

These books are (long?) out of print, but they still seem to be available quite cheaply secondhand on the internet.

And, as I said before, I'd guess that springs are still treated in some engineering textbooks.
 
Last edited:
Ok Thanks a lot...
 

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